update

.CondaPkg/env/Lib/site-packages/scipy/sparse/linalg/_isolve/__init__.py

@@ -0,0 +1,20 @@
+"Iterative Solvers for Sparse Linear Systems"
+
+#from info import __doc__
+from .iterative import *
+from .minres import minres
+from .lgmres import lgmres
+from .lsqr import lsqr
+from .lsmr import lsmr
+from ._gcrotmk import gcrotmk
+from .tfqmr import tfqmr
+
+__all__ = [
+    'bicg', 'bicgstab', 'cg', 'cgs', 'gcrotmk', 'gmres',
+    'lgmres', 'lsmr', 'lsqr',
+    'minres', 'qmr', 'tfqmr'
+]
+
+from scipy._lib._testutils import PytestTester
+test = PytestTester(__name__)
+del PytestTester

.CondaPkg/env/Lib/site-packages/scipy/sparse/linalg/_isolve/_gcrotmk.py

@@ -0,0 +1,501 @@
+# Copyright (C) 2015, Pauli Virtanen <pav@iki.fi>
+# Distributed under the same license as SciPy.
+
+import numpy as np
+from numpy.linalg import LinAlgError
+from scipy.linalg import (get_blas_funcs, qr, solve, svd, qr_insert, lstsq)
+from .iterative import _get_atol_rtol
+from scipy.sparse.linalg._isolve.utils import make_system
+
+
+__all__ = ['gcrotmk']
+
+
+def _fgmres(matvec, v0, m, atol, lpsolve=None, rpsolve=None, cs=(), outer_v=(),
+            prepend_outer_v=False):
+    """
+    FGMRES Arnoldi process, with optional projection or augmentation
+
+    Parameters
+    ----------
+    matvec : callable
+        Operation A*x
+    v0 : ndarray
+        Initial vector, normalized to nrm2(v0) == 1
+    m : int
+        Number of GMRES rounds
+    atol : float
+        Absolute tolerance for early exit
+    lpsolve : callable
+        Left preconditioner L
+    rpsolve : callable
+        Right preconditioner R
+    cs : list of (ndarray, ndarray)
+        Columns of matrices C and U in GCROT
+    outer_v : list of ndarrays
+        Augmentation vectors in LGMRES
+    prepend_outer_v : bool, optional
+        Whether augmentation vectors come before or after
+        Krylov iterates
+
+    Raises
+    ------
+    LinAlgError
+        If nans encountered
+
+    Returns
+    -------
+    Q, R : ndarray
+        QR decomposition of the upper Hessenberg H=QR
+    B : ndarray
+        Projections corresponding to matrix C
+    vs : list of ndarray
+        Columns of matrix V
+    zs : list of ndarray
+        Columns of matrix Z
+    y : ndarray
+        Solution to ||H y - e_1||_2 = min!
+    res : float
+        The final (preconditioned) residual norm
+
+    """
+
+    if lpsolve is None:
+        def lpsolve(x):
+            return x
+    if rpsolve is None:
+        def rpsolve(x):
+            return x
+
+    axpy, dot, scal, nrm2 = get_blas_funcs(['axpy', 'dot', 'scal', 'nrm2'], (v0,))
+
+    vs = [v0]
+    zs = []
+    y = None
+    res = np.nan
+
+    m = m + len(outer_v)
+
+    # Orthogonal projection coefficients
+    B = np.zeros((len(cs), m), dtype=v0.dtype)
+
+    # H is stored in QR factorized form
+    Q = np.ones((1, 1), dtype=v0.dtype)
+    R = np.zeros((1, 0), dtype=v0.dtype)
+
+    eps = np.finfo(v0.dtype).eps
+
+    breakdown = False
+
+    # FGMRES Arnoldi process
+    for j in range(m):
+        # L A Z = C B + V H
+
+        if prepend_outer_v and j < len(outer_v):
+            z, w = outer_v[j]
+        elif prepend_outer_v and j == len(outer_v):
+            z = rpsolve(v0)
+            w = None
+        elif not prepend_outer_v and j >= m - len(outer_v):
+            z, w = outer_v[j - (m - len(outer_v))]
+        else:
+            z = rpsolve(vs[-1])
+            w = None
+
+        if w is None:
+            w = lpsolve(matvec(z))
+        else:
+            # w is clobbered below
+            w = w.copy()
+
+        w_norm = nrm2(w)
+
+        # GCROT projection: L A -> (1 - C C^H) L A
+        # i.e. orthogonalize against C
+        for i, c in enumerate(cs):
+            alpha = dot(c, w)
+            B[i,j] = alpha
+            w = axpy(c, w, c.shape[0], -alpha)  # w -= alpha*c
+
+        # Orthogonalize against V
+        hcur = np.zeros(j+2, dtype=Q.dtype)
+        for i, v in enumerate(vs):
+            alpha = dot(v, w)
+            hcur[i] = alpha
+            w = axpy(v, w, v.shape[0], -alpha)  # w -= alpha*v
+        hcur[i+1] = nrm2(w)
+
+        with np.errstate(over='ignore', divide='ignore'):
+            # Careful with denormals
+            alpha = 1/hcur[-1]
+
+        if np.isfinite(alpha):
+            w = scal(alpha, w)
+
+        if not (hcur[-1] > eps * w_norm):
+            # w essentially in the span of previous vectors,
+            # or we have nans. Bail out after updating the QR
+            # solution.
+            breakdown = True
+
+        vs.append(w)
+        zs.append(z)
+
+        # Arnoldi LSQ problem
+
+        # Add new column to H=Q@R, padding other columns with zeros
+        Q2 = np.zeros((j+2, j+2), dtype=Q.dtype, order='F')
+        Q2[:j+1,:j+1] = Q
+        Q2[j+1,j+1] = 1
+
+        R2 = np.zeros((j+2, j), dtype=R.dtype, order='F')
+        R2[:j+1,:] = R
+
+        Q, R = qr_insert(Q2, R2, hcur, j, which='col',
+                         overwrite_qru=True, check_finite=False)
+
+        # Transformed least squares problem
+        # || Q R y - inner_res_0 * e_1 ||_2 = min!
+        # Since R = [R'; 0], solution is y = inner_res_0 (R')^{-1} (Q^H)[:j,0]
+
+        # Residual is immediately known
+        res = abs(Q[0,-1])
+
+        # Check for termination
+        if res < atol or breakdown:
+            break
+
+    if not np.isfinite(R[j,j]):
+        # nans encountered, bail out
+        raise LinAlgError()
+
+    # -- Get the LSQ problem solution
+
+    # The problem is triangular, but the condition number may be
+    # bad (or in case of breakdown the last diagonal entry may be
+    # zero), so use lstsq instead of trtrs.
+    y, _, _, _, = lstsq(R[:j+1,:j+1], Q[0,:j+1].conj())
+
+    B = B[:,:j+1]
+
+    return Q, R, B, vs, zs, y, res
+
+
+def gcrotmk(A, b, x0=None, *, rtol=1e-5, atol=0., maxiter=1000, M=None, callback=None,
+            m=20, k=None, CU=None, discard_C=False, truncate='oldest'):
+    """
+    Solve a matrix equation using flexible GCROT(m,k) algorithm.
+
+    Parameters
+    ----------
+    A : {sparse matrix, ndarray, LinearOperator}
+        The real or complex N-by-N matrix of the linear system.
+        Alternatively, ``A`` can be a linear operator which can
+        produce ``Ax`` using, e.g.,
+        ``scipy.sparse.linalg.LinearOperator``.
+    b : ndarray
+        Right hand side of the linear system. Has shape (N,) or (N,1).
+    x0 : ndarray
+        Starting guess for the solution.
+    rtol, atol : float, optional
+        Parameters for the convergence test. For convergence,
+        ``norm(b - A @ x) <= max(rtol*norm(b), atol)`` should be satisfied.
+        The default is ``rtol=1e-5``, the default for ``atol`` is ``0.0``.
+    maxiter : int, optional
+        Maximum number of iterations.  Iteration will stop after maxiter
+        steps even if the specified tolerance has not been achieved.
+    M : {sparse matrix, ndarray, LinearOperator}, optional
+        Preconditioner for A.  The preconditioner should approximate the
+        inverse of A. gcrotmk is a 'flexible' algorithm and the preconditioner
+        can vary from iteration to iteration. Effective preconditioning
+        dramatically improves the rate of convergence, which implies that
+        fewer iterations are needed to reach a given error tolerance.
+    callback : function, optional
+        User-supplied function to call after each iteration.  It is called
+        as callback(xk), where xk is the current solution vector.
+    m : int, optional
+        Number of inner FGMRES iterations per each outer iteration.
+        Default: 20
+    k : int, optional
+        Number of vectors to carry between inner FGMRES iterations.
+        According to [2]_, good values are around m.
+        Default: m
+    CU : list of tuples, optional
+        List of tuples ``(c, u)`` which contain the columns of the matrices
+        C and U in the GCROT(m,k) algorithm. For details, see [2]_.
+        The list given and vectors contained in it are modified in-place.
+        If not given, start from empty matrices. The ``c`` elements in the
+        tuples can be ``None``, in which case the vectors are recomputed
+        via ``c = A u`` on start and orthogonalized as described in [3]_.
+    discard_C : bool, optional
+        Discard the C-vectors at the end. Useful if recycling Krylov subspaces
+        for different linear systems.
+    truncate : {'oldest', 'smallest'}, optional
+        Truncation scheme to use. Drop: oldest vectors, or vectors with
+        smallest singular values using the scheme discussed in [1,2].
+        See [2]_ for detailed comparison.
+        Default: 'oldest'
+
+    Returns
+    -------
+    x : ndarray
+        The solution found.
+    info : int
+        Provides convergence information:
+
+        * 0  : successful exit
+        * >0 : convergence to tolerance not achieved, number of iterations
+
+    Examples
+    --------
+    >>> import numpy as np
+    >>> from scipy.sparse import csc_matrix
+    >>> from scipy.sparse.linalg import gcrotmk
+    >>> R = np.random.randn(5, 5)
+    >>> A = csc_matrix(R)
+    >>> b = np.random.randn(5)
+    >>> x, exit_code = gcrotmk(A, b, atol=1e-5)
+    >>> print(exit_code)
+    0
+    >>> np.allclose(A.dot(x), b)
+    True
+
+    References
+    ----------
+    .. [1] E. de Sturler, ''Truncation strategies for optimal Krylov subspace
+           methods'', SIAM J. Numer. Anal. 36, 864 (1999).
+    .. [2] J.E. Hicken and D.W. Zingg, ''A simplified and flexible variant
+           of GCROT for solving nonsymmetric linear systems'',
+           SIAM J. Sci. Comput. 32, 172 (2010).
+    .. [3] M.L. Parks, E. de Sturler, G. Mackey, D.D. Johnson, S. Maiti,
+           ''Recycling Krylov subspaces for sequences of linear systems'',
+           SIAM J. Sci. Comput. 28, 1651 (2006).
+
+    """
+    A,M,x,b,postprocess = make_system(A,M,x0,b)
+
+    if not np.isfinite(b).all():
+        raise ValueError("RHS must contain only finite numbers")
+
+    if truncate not in ('oldest', 'smallest'):
+        raise ValueError(f"Invalid value for 'truncate': {truncate!r}")
+
+    matvec = A.matvec
+    psolve = M.matvec
+
+    if CU is None:
+        CU = []
+
+    if k is None:
+        k = m
+
+    axpy, dot, scal = None, None, None
+
+    if x0 is None:
+        r = b.copy()
+    else:
+        r = b - matvec(x)
+
+    axpy, dot, scal, nrm2 = get_blas_funcs(['axpy', 'dot', 'scal', 'nrm2'], (x, r))
+
+    b_norm = nrm2(b)
+
+    # we call this to get the right atol/rtol and raise errors as necessary
+    atol, rtol = _get_atol_rtol('gcrotmk', b_norm, atol, rtol)
+
+    if b_norm == 0:
+        x = b
+        return (postprocess(x), 0)
+
+    if discard_C:
+        CU[:] = [(None, u) for c, u in CU]
+
+    # Reorthogonalize old vectors
+    if CU:
+        # Sort already existing vectors to the front
+        CU.sort(key=lambda cu: cu[0] is not None)
+
+        # Fill-in missing ones
+        C = np.empty((A.shape[0], len(CU)), dtype=r.dtype, order='F')
+        us = []
+        j = 0
+        while CU:
+            # More memory-efficient: throw away old vectors as we go
+            c, u = CU.pop(0)
+            if c is None:
+                c = matvec(u)
+            C[:,j] = c
+            j += 1
+            us.append(u)
+
+        # Orthogonalize
+        Q, R, P = qr(C, overwrite_a=True, mode='economic', pivoting=True)
+        del C
+
+        # C := Q
+        cs = list(Q.T)
+
+        # U := U P R^-1,  back-substitution
+        new_us = []
+        for j in range(len(cs)):
+            u = us[P[j]]
+            for i in range(j):
+                u = axpy(us[P[i]], u, u.shape[0], -R[i,j])
+            if abs(R[j,j]) < 1e-12 * abs(R[0,0]):
+                # discard rest of the vectors
+                break
+            u = scal(1.0/R[j,j], u)
+            new_us.append(u)
+
+        # Form the new CU lists
+        CU[:] = list(zip(cs, new_us))[::-1]
+
+    if CU:
+        axpy, dot = get_blas_funcs(['axpy', 'dot'], (r,))
+
+        # Solve first the projection operation with respect to the CU
+        # vectors. This corresponds to modifying the initial guess to
+        # be
+        #
+        #     x' = x + U y
+        #     y = argmin_y || b - A (x + U y) ||^2
+        #
+        # The solution is y = C^H (b - A x)
+        for c, u in CU:
+            yc = dot(c, r)
+            x = axpy(u, x, x.shape[0], yc)
+            r = axpy(c, r, r.shape[0], -yc)
+
+    # GCROT main iteration
+    for j_outer in range(maxiter):
+        # -- callback
+        if callback is not None:
+            callback(x)
+
+        beta = nrm2(r)
+
+        # -- check stopping condition
+        beta_tol = max(atol, rtol * b_norm)
+
+        if beta <= beta_tol and (j_outer > 0 or CU):
+            # recompute residual to avoid rounding error
+            r = b - matvec(x)
+            beta = nrm2(r)
+
+        if beta <= beta_tol:
+            j_outer = -1
+            break
+
+        ml = m + max(k - len(CU), 0)
+
+        cs = [c for c, u in CU]
+
+        try:
+            Q, R, B, vs, zs, y, pres = _fgmres(matvec,
+                                               r/beta,
+                                               ml,
+                                               rpsolve=psolve,
+                                               atol=max(atol, rtol*b_norm)/beta,
+                                               cs=cs)
+            y *= beta
+        except LinAlgError:
+            # Floating point over/underflow, non-finite result from
+            # matmul etc. -- report failure.
+            break
+
+        #
+        # At this point,
+        #
+        #     [A U, A Z] = [C, V] G;   G =  [ I  B ]
+        #                                   [ 0  H ]
+        #
+        # where [C, V] has orthonormal columns, and r = beta v_0. Moreover,
+        #
+        #     || b - A (x + Z y + U q) ||_2 = || r - C B y - V H y - C q ||_2 = min!
+        #
+        # from which y = argmin_y || beta e_1 - H y ||_2, and q = -B y
+        #
+
+        #
+        # GCROT(m,k) update
+        #
+
+        # Define new outer vectors
+
+        # ux := (Z - U B) y
+        ux = zs[0]*y[0]
+        for z, yc in zip(zs[1:], y[1:]):
+            ux = axpy(z, ux, ux.shape[0], yc)  # ux += z*yc
+        by = B.dot(y)
+        for cu, byc in zip(CU, by):
+            c, u = cu
+            ux = axpy(u, ux, ux.shape[0], -byc)  # ux -= u*byc
+
+        # cx := V H y
+        hy = Q.dot(R.dot(y))
+        cx = vs[0] * hy[0]
+        for v, hyc in zip(vs[1:], hy[1:]):
+            cx = axpy(v, cx, cx.shape[0], hyc)  # cx += v*hyc
+
+        # Normalize cx, maintaining cx = A ux
+        # This new cx is orthogonal to the previous C, by construction
+        try:
+            alpha = 1/nrm2(cx)
+            if not np.isfinite(alpha):
+                raise FloatingPointError()
+        except (FloatingPointError, ZeroDivisionError):
+            # Cannot update, so skip it
+            continue
+
+        cx = scal(alpha, cx)
+        ux = scal(alpha, ux)
+
+        # Update residual and solution
+        gamma = dot(cx, r)
+        r = axpy(cx, r, r.shape[0], -gamma)  # r -= gamma*cx
+        x = axpy(ux, x, x.shape[0], gamma)  # x += gamma*ux
+
+        # Truncate CU
+        if truncate == 'oldest':
+            while len(CU) >= k and CU:
+                del CU[0]
+        elif truncate == 'smallest':
+            if len(CU) >= k and CU:
+                # cf. [1,2]
+                D = solve(R[:-1,:].T, B.T).T
+                W, sigma, V = svd(D)
+
+                # C := C W[:,:k-1],  U := U W[:,:k-1]
+                new_CU = []
+                for j, w in enumerate(W[:,:k-1].T):
+                    c, u = CU[0]
+                    c = c * w[0]
+                    u = u * w[0]
+                    for cup, wp in zip(CU[1:], w[1:]):
+                        cp, up = cup
+                        c = axpy(cp, c, c.shape[0], wp)
+                        u = axpy(up, u, u.shape[0], wp)
+
+                    # Reorthogonalize at the same time; not necessary
+                    # in exact arithmetic, but floating point error
+                    # tends to accumulate here
+                    for cp, up in new_CU:
+                        alpha = dot(cp, c)
+                        c = axpy(cp, c, c.shape[0], -alpha)
+                        u = axpy(up, u, u.shape[0], -alpha)
+                    alpha = nrm2(c)
+                    c = scal(1.0/alpha, c)
+                    u = scal(1.0/alpha, u)
+
+                    new_CU.append((c, u))
+                CU[:] = new_CU
+
+        # Add new vector to CU
+        CU.append((cx, ux))
+
+    # Include the solution vector to the span
+    CU.append((None, x.copy()))
+    if discard_C:
+        CU[:] = [(None, uz) for cz, uz in CU]
+
+    return postprocess(x), j_outer + 1

.CondaPkg/env/Lib/site-packages/scipy/sparse/linalg/_isolve/lgmres.py

@@ -0,0 +1,230 @@
+# Copyright (C) 2009, Pauli Virtanen <pav@iki.fi>
+# Distributed under the same license as SciPy.
+
+import numpy as np
+from numpy.linalg import LinAlgError
+from scipy.linalg import get_blas_funcs
+from .iterative import _get_atol_rtol
+from .utils import make_system
+
+from ._gcrotmk import _fgmres
+
+__all__ = ['lgmres']
+
+
+def lgmres(A, b, x0=None, *, rtol=1e-5, atol=0., maxiter=1000, M=None, callback=None,
+           inner_m=30, outer_k=3, outer_v=None, store_outer_Av=True,
+           prepend_outer_v=False):
+    """
+    Solve a matrix equation using the LGMRES algorithm.
+
+    The LGMRES algorithm [1]_ [2]_ is designed to avoid some problems
+    in the convergence in restarted GMRES, and often converges in fewer
+    iterations.
+
+    Parameters
+    ----------
+    A : {sparse matrix, ndarray, LinearOperator}
+        The real or complex N-by-N matrix of the linear system.
+        Alternatively, ``A`` can be a linear operator which can
+        produce ``Ax`` using, e.g.,
+        ``scipy.sparse.linalg.LinearOperator``.
+    b : ndarray
+        Right hand side of the linear system. Has shape (N,) or (N,1).
+    x0 : ndarray
+        Starting guess for the solution.
+    rtol, atol : float, optional
+        Parameters for the convergence test. For convergence,
+        ``norm(b - A @ x) <= max(rtol*norm(b), atol)`` should be satisfied.
+        The default is ``rtol=1e-5``, the default for ``atol`` is ``0.0``.
+    maxiter : int, optional
+        Maximum number of iterations.  Iteration will stop after maxiter
+        steps even if the specified tolerance has not been achieved.
+    M : {sparse matrix, ndarray, LinearOperator}, optional
+        Preconditioner for A.  The preconditioner should approximate the
+        inverse of A.  Effective preconditioning dramatically improves the
+        rate of convergence, which implies that fewer iterations are needed
+        to reach a given error tolerance.
+    callback : function, optional
+        User-supplied function to call after each iteration.  It is called
+        as callback(xk), where xk is the current solution vector.
+    inner_m : int, optional
+        Number of inner GMRES iterations per each outer iteration.
+    outer_k : int, optional
+        Number of vectors to carry between inner GMRES iterations.
+        According to [1]_, good values are in the range of 1...3.
+        However, note that if you want to use the additional vectors to
+        accelerate solving multiple similar problems, larger values may
+        be beneficial.
+    outer_v : list of tuples, optional
+        List containing tuples ``(v, Av)`` of vectors and corresponding
+        matrix-vector products, used to augment the Krylov subspace, and
+        carried between inner GMRES iterations. The element ``Av`` can
+        be `None` if the matrix-vector product should be re-evaluated.
+        This parameter is modified in-place by `lgmres`, and can be used
+        to pass "guess" vectors in and out of the algorithm when solving
+        similar problems.
+    store_outer_Av : bool, optional
+        Whether LGMRES should store also A@v in addition to vectors `v`
+        in the `outer_v` list. Default is True.
+    prepend_outer_v : bool, optional
+        Whether to put outer_v augmentation vectors before Krylov iterates.
+        In standard LGMRES, prepend_outer_v=False.
+
+    Returns
+    -------
+    x : ndarray
+        The converged solution.
+    info : int
+        Provides convergence information:
+
+            - 0  : successful exit
+            - >0 : convergence to tolerance not achieved, number of iterations
+            - <0 : illegal input or breakdown
+
+    Notes
+    -----
+    The LGMRES algorithm [1]_ [2]_ is designed to avoid the
+    slowing of convergence in restarted GMRES, due to alternating
+    residual vectors. Typically, it often outperforms GMRES(m) of
+    comparable memory requirements by some measure, or at least is not
+    much worse.
+
+    Another advantage in this algorithm is that you can supply it with
+    'guess' vectors in the `outer_v` argument that augment the Krylov
+    subspace. If the solution lies close to the span of these vectors,
+    the algorithm converges faster. This can be useful if several very
+    similar matrices need to be inverted one after another, such as in
+    Newton-Krylov iteration where the Jacobian matrix often changes
+    little in the nonlinear steps.
+
+    References
+    ----------
+    .. [1] A.H. Baker and E.R. Jessup and T. Manteuffel, "A Technique for
+             Accelerating the Convergence of Restarted GMRES", SIAM J. Matrix
+             Anal. Appl. 26, 962 (2005).
+    .. [2] A.H. Baker, "On Improving the Performance of the Linear Solver
+             restarted GMRES", PhD thesis, University of Colorado (2003).
+
+    Examples
+    --------
+    >>> import numpy as np
+    >>> from scipy.sparse import csc_matrix
+    >>> from scipy.sparse.linalg import lgmres
+    >>> A = csc_matrix([[3, 2, 0], [1, -1, 0], [0, 5, 1]], dtype=float)
+    >>> b = np.array([2, 4, -1], dtype=float)
+    >>> x, exitCode = lgmres(A, b, atol=1e-5)
+    >>> print(exitCode)            # 0 indicates successful convergence
+    0
+    >>> np.allclose(A.dot(x), b)
+    True
+    """
+    A,M,x,b,postprocess = make_system(A,M,x0,b)
+
+    if not np.isfinite(b).all():
+        raise ValueError("RHS must contain only finite numbers")
+
+    matvec = A.matvec
+    psolve = M.matvec
+
+    if outer_v is None:
+        outer_v = []
+
+    axpy, dot, scal = None, None, None
+    nrm2 = get_blas_funcs('nrm2', [b])
+
+    b_norm = nrm2(b)
+
+    # we call this to get the right atol/rtol and raise errors as necessary
+    atol, rtol = _get_atol_rtol('lgmres', b_norm, atol, rtol)
+
+    if b_norm == 0:
+        x = b
+        return (postprocess(x), 0)
+
+    ptol_max_factor = 1.0
+
+    for k_outer in range(maxiter):
+        r_outer = matvec(x) - b
+
+        # -- callback
+        if callback is not None:
+            callback(x)
+
+        # -- determine input type routines
+        if axpy is None:
+            if np.iscomplexobj(r_outer) and not np.iscomplexobj(x):
+                x = x.astype(r_outer.dtype)
+            axpy, dot, scal, nrm2 = get_blas_funcs(['axpy', 'dot', 'scal', 'nrm2'],
+                                                   (x, r_outer))
+
+        # -- check stopping condition
+        r_norm = nrm2(r_outer)
+        if r_norm <= max(atol, rtol * b_norm):
+            break
+
+        # -- inner LGMRES iteration
+        v0 = -psolve(r_outer)
+        inner_res_0 = nrm2(v0)
+
+        if inner_res_0 == 0:
+            rnorm = nrm2(r_outer)
+            raise RuntimeError("Preconditioner returned a zero vector; "
+                               "|v| ~ %.1g, |M v| = 0" % rnorm)
+
+        v0 = scal(1.0/inner_res_0, v0)
+
+        ptol = min(ptol_max_factor, max(atol, rtol*b_norm)/r_norm)
+
+        try:
+            Q, R, B, vs, zs, y, pres = _fgmres(matvec,
+                                               v0,
+                                               inner_m,
+                                               lpsolve=psolve,
+                                               atol=ptol,
+                                               outer_v=outer_v,
+                                               prepend_outer_v=prepend_outer_v)
+            y *= inner_res_0
+            if not np.isfinite(y).all():
+                # Overflow etc. in computation. There's no way to
+                # recover from this, so we have to bail out.
+                raise LinAlgError()
+        except LinAlgError:
+            # Floating point over/underflow, non-finite result from
+            # matmul etc. -- report failure.
+            return postprocess(x), k_outer + 1
+
+        # Inner loop tolerance control
+        if pres > ptol:
+            ptol_max_factor = min(1.0, 1.5 * ptol_max_factor)
+        else:
+            ptol_max_factor = max(1e-16, 0.25 * ptol_max_factor)
+
+        # -- GMRES terminated: eval solution
+        dx = zs[0]*y[0]
+        for w, yc in zip(zs[1:], y[1:]):
+            dx = axpy(w, dx, dx.shape[0], yc)  # dx += w*yc
+
+        # -- Store LGMRES augmentation vectors
+        nx = nrm2(dx)
+        if nx > 0:
+            if store_outer_Av:
+                q = Q.dot(R.dot(y))
+                ax = vs[0]*q[0]
+                for v, qc in zip(vs[1:], q[1:]):
+                    ax = axpy(v, ax, ax.shape[0], qc)
+                outer_v.append((dx/nx, ax/nx))
+            else:
+                outer_v.append((dx/nx, None))
+
+        # -- Retain only a finite number of augmentation vectors
+        while len(outer_v) > outer_k:
+            del outer_v[0]
+
+        # -- Apply step
+        x += dx
+    else:
+        # didn't converge ...
+        return postprocess(x), maxiter
+
+    return postprocess(x), 0

.CondaPkg/env/Lib/site-packages/scipy/sparse/linalg/_isolve/lsmr.py

@@ -0,0 +1,486 @@
+"""
+Copyright (C) 2010 David Fong and Michael Saunders
+
+LSMR uses an iterative method.
+
+07 Jun 2010: Documentation updated
+03 Jun 2010: First release version in Python
+
+David Chin-lung Fong            clfong@stanford.edu
+Institute for Computational and Mathematical Engineering
+Stanford University
+
+Michael Saunders                saunders@stanford.edu
+Systems Optimization Laboratory
+Dept of MS&E, Stanford University.
+
+"""
+
+__all__ = ['lsmr']
+
+from numpy import zeros, inf, atleast_1d, result_type
+from numpy.linalg import norm
+from math import sqrt
+from scipy.sparse.linalg._interface import aslinearoperator
+
+from scipy.sparse.linalg._isolve.lsqr import _sym_ortho
+
+
+def lsmr(A, b, damp=0.0, atol=1e-6, btol=1e-6, conlim=1e8,
+         maxiter=None, show=False, x0=None):
+    """Iterative solver for least-squares problems.
+
+    lsmr solves the system of linear equations ``Ax = b``. If the system
+    is inconsistent, it solves the least-squares problem ``min ||b - Ax||_2``.
+    ``A`` is a rectangular matrix of dimension m-by-n, where all cases are
+    allowed: m = n, m > n, or m < n. ``b`` is a vector of length m.
+    The matrix A may be dense or sparse (usually sparse).
+
+    Parameters
+    ----------
+    A : {sparse matrix, ndarray, LinearOperator}
+        Matrix A in the linear system.
+        Alternatively, ``A`` can be a linear operator which can
+        produce ``Ax`` and ``A^H x`` using, e.g.,
+        ``scipy.sparse.linalg.LinearOperator``.
+    b : array_like, shape (m,)
+        Vector ``b`` in the linear system.
+    damp : float
+        Damping factor for regularized least-squares. `lsmr` solves
+        the regularized least-squares problem::
+
+         min ||(b) - (  A   )x||
+             ||(0)   (damp*I) ||_2
+
+        where damp is a scalar.  If damp is None or 0, the system
+        is solved without regularization. Default is 0.
+    atol, btol : float, optional
+        Stopping tolerances. `lsmr` continues iterations until a
+        certain backward error estimate is smaller than some quantity
+        depending on atol and btol.  Let ``r = b - Ax`` be the
+        residual vector for the current approximate solution ``x``.
+        If ``Ax = b`` seems to be consistent, `lsmr` terminates
+        when ``norm(r) <= atol * norm(A) * norm(x) + btol * norm(b)``.
+        Otherwise, `lsmr` terminates when ``norm(A^H r) <=
+        atol * norm(A) * norm(r)``.  If both tolerances are 1.0e-6 (default),
+        the final ``norm(r)`` should be accurate to about 6
+        digits. (The final ``x`` will usually have fewer correct digits,
+        depending on ``cond(A)`` and the size of LAMBDA.)  If `atol`
+        or `btol` is None, a default value of 1.0e-6 will be used.
+        Ideally, they should be estimates of the relative error in the
+        entries of ``A`` and ``b`` respectively.  For example, if the entries
+        of ``A`` have 7 correct digits, set ``atol = 1e-7``. This prevents
+        the algorithm from doing unnecessary work beyond the
+        uncertainty of the input data.
+    conlim : float, optional
+        `lsmr` terminates if an estimate of ``cond(A)`` exceeds
+        `conlim`.  For compatible systems ``Ax = b``, conlim could be
+        as large as 1.0e+12 (say).  For least-squares problems,
+        `conlim` should be less than 1.0e+8. If `conlim` is None, the
+        default value is 1e+8.  Maximum precision can be obtained by
+        setting ``atol = btol = conlim = 0``, but the number of
+        iterations may then be excessive. Default is 1e8.
+    maxiter : int, optional
+        `lsmr` terminates if the number of iterations reaches
+        `maxiter`.  The default is ``maxiter = min(m, n)``.  For
+        ill-conditioned systems, a larger value of `maxiter` may be
+        needed. Default is False.
+    show : bool, optional
+        Print iterations logs if ``show=True``. Default is False.
+    x0 : array_like, shape (n,), optional
+        Initial guess of ``x``, if None zeros are used. Default is None.
+
+        .. versionadded:: 1.0.0
+
+    Returns
+    -------
+    x : ndarray of float
+        Least-square solution returned.
+    istop : int
+        istop gives the reason for stopping::
+
+          istop   = 0 means x=0 is a solution.  If x0 was given, then x=x0 is a
+                      solution.
+                  = 1 means x is an approximate solution to A@x = B,
+                      according to atol and btol.
+                  = 2 means x approximately solves the least-squares problem
+                      according to atol.
+                  = 3 means COND(A) seems to be greater than CONLIM.
+                  = 4 is the same as 1 with atol = btol = eps (machine
+                      precision)
+                  = 5 is the same as 2 with atol = eps.
+                  = 6 is the same as 3 with CONLIM = 1/eps.
+                  = 7 means ITN reached maxiter before the other stopping
+                      conditions were satisfied.
+
+    itn : int
+        Number of iterations used.
+    normr : float
+        ``norm(b-Ax)``
+    normar : float
+        ``norm(A^H (b - Ax))``
+    norma : float
+        ``norm(A)``
+    conda : float
+        Condition number of A.
+    normx : float
+        ``norm(x)``
+
+    Notes
+    -----
+
+    .. versionadded:: 0.11.0
+
+    References
+    ----------
+    .. [1] D. C.-L. Fong and M. A. Saunders,
+           "LSMR: An iterative algorithm for sparse least-squares problems",
+           SIAM J. Sci. Comput., vol. 33, pp. 2950-2971, 2011.
+           :arxiv:`1006.0758`
+    .. [2] LSMR Software, https://web.stanford.edu/group/SOL/software/lsmr/
+
+    Examples
+    --------
+    >>> import numpy as np
+    >>> from scipy.sparse import csc_matrix
+    >>> from scipy.sparse.linalg import lsmr
+    >>> A = csc_matrix([[1., 0.], [1., 1.], [0., 1.]], dtype=float)
+
+    The first example has the trivial solution ``[0, 0]``
+
+    >>> b = np.array([0., 0., 0.], dtype=float)
+    >>> x, istop, itn, normr = lsmr(A, b)[:4]
+    >>> istop
+    0
+    >>> x
+    array([0., 0.])
+
+    The stopping code `istop=0` returned indicates that a vector of zeros was
+    found as a solution. The returned solution `x` indeed contains
+    ``[0., 0.]``. The next example has a non-trivial solution:
+
+    >>> b = np.array([1., 0., -1.], dtype=float)
+    >>> x, istop, itn, normr = lsmr(A, b)[:4]
+    >>> istop
+    1
+    >>> x
+    array([ 1., -1.])
+    >>> itn
+    1
+    >>> normr
+    4.440892098500627e-16
+
+    As indicated by `istop=1`, `lsmr` found a solution obeying the tolerance
+    limits. The given solution ``[1., -1.]`` obviously solves the equation. The
+    remaining return values include information about the number of iterations
+    (`itn=1`) and the remaining difference of left and right side of the solved
+    equation.
+    The final example demonstrates the behavior in the case where there is no
+    solution for the equation:
+
+    >>> b = np.array([1., 0.01, -1.], dtype=float)
+    >>> x, istop, itn, normr = lsmr(A, b)[:4]
+    >>> istop
+    2
+    >>> x
+    array([ 1.00333333, -0.99666667])
+    >>> A.dot(x)-b
+    array([ 0.00333333, -0.00333333,  0.00333333])
+    >>> normr
+    0.005773502691896255
+
+    `istop` indicates that the system is inconsistent and thus `x` is rather an
+    approximate solution to the corresponding least-squares problem. `normr`
+    contains the minimal distance that was found.
+    """
+
+    A = aslinearoperator(A)
+    b = atleast_1d(b)
+    if b.ndim > 1:
+        b = b.squeeze()
+
+    msg = ('The exact solution is x = 0, or x = x0, if x0 was given  ',
+           'Ax - b is small enough, given atol, btol                  ',
+           'The least-squares solution is good enough, given atol     ',
+           'The estimate of cond(Abar) has exceeded conlim            ',
+           'Ax - b is small enough for this machine                   ',
+           'The least-squares solution is good enough for this machine',
+           'Cond(Abar) seems to be too large for this machine         ',
+           'The iteration limit has been reached                      ')
+
+    hdg1 = '   itn      x(1)       norm r    norm Ar'
+    hdg2 = ' compatible   LS      norm A   cond A'
+    pfreq = 20   # print frequency (for repeating the heading)
+    pcount = 0   # print counter
+
+    m, n = A.shape
+
+    # stores the num of singular values
+    minDim = min([m, n])
+
+    if maxiter is None:
+        maxiter = minDim
+
+    if x0 is None:
+        dtype = result_type(A, b, float)
+    else:
+        dtype = result_type(A, b, x0, float)
+
+    if show:
+        print(' ')
+        print('LSMR            Least-squares solution of  Ax = b\n')
+        print(f'The matrix A has {m} rows and {n} columns')
+        print('damp = %20.14e\n' % (damp))
+        print(f'atol = {atol:8.2e}                 conlim = {conlim:8.2e}\n')
+        print(f'btol = {btol:8.2e}             maxiter = {maxiter:8g}\n')
+
+    u = b
+    normb = norm(b)
+    if x0 is None:
+        x = zeros(n, dtype)
+        beta = normb.copy()
+    else:
+        x = atleast_1d(x0.copy())
+        u = u - A.matvec(x)
+        beta = norm(u)
+
+    if beta > 0:
+        u = (1 / beta) * u
+        v = A.rmatvec(u)
+        alpha = norm(v)
+    else:
+        v = zeros(n, dtype)
+        alpha = 0
+
+    if alpha > 0:
+        v = (1 / alpha) * v
+
+    # Initialize variables for 1st iteration.
+
+    itn = 0
+    zetabar = alpha * beta
+    alphabar = alpha
+    rho = 1
+    rhobar = 1
+    cbar = 1
+    sbar = 0
+
+    h = v.copy()
+    hbar = zeros(n, dtype)
+
+    # Initialize variables for estimation of ||r||.
+
+    betadd = beta
+    betad = 0
+    rhodold = 1
+    tautildeold = 0
+    thetatilde = 0
+    zeta = 0
+    d = 0
+
+    # Initialize variables for estimation of ||A|| and cond(A)
+
+    normA2 = alpha * alpha
+    maxrbar = 0
+    minrbar = 1e+100
+    normA = sqrt(normA2)
+    condA = 1
+    normx = 0
+
+    # Items for use in stopping rules, normb set earlier
+    istop = 0
+    ctol = 0
+    if conlim > 0:
+        ctol = 1 / conlim
+    normr = beta
+
+    # Reverse the order here from the original matlab code because
+    # there was an error on return when arnorm==0
+    normar = alpha * beta
+    if normar == 0:
+        if show:
+            print(msg[0])
+        return x, istop, itn, normr, normar, normA, condA, normx
+
+    if normb == 0:
+        x[()] = 0
+        return x, istop, itn, normr, normar, normA, condA, normx
+
+    if show:
+        print(' ')
+        print(hdg1, hdg2)
+        test1 = 1
+        test2 = alpha / beta
+        str1 = f'{itn:6g} {x[0]:12.5e}'
+        str2 = f' {normr:10.3e} {normar:10.3e}'
+        str3 = f'  {test1:8.1e} {test2:8.1e}'
+        print(''.join([str1, str2, str3]))
+
+    # Main iteration loop.
+    while itn < maxiter:
+        itn = itn + 1
+
+        # Perform the next step of the bidiagonalization to obtain the
+        # next  beta, u, alpha, v.  These satisfy the relations
+        #         beta*u  =  A@v   -  alpha*u,
+        #        alpha*v  =  A'@u  -  beta*v.
+
+        u *= -alpha
+        u += A.matvec(v)
+        beta = norm(u)
+
+        if beta > 0:
+            u *= (1 / beta)
+            v *= -beta
+            v += A.rmatvec(u)
+            alpha = norm(v)
+            if alpha > 0:
+                v *= (1 / alpha)
+
+        # At this point, beta = beta_{k+1}, alpha = alpha_{k+1}.
+
+        # Construct rotation Qhat_{k,2k+1}.
+
+        chat, shat, alphahat = _sym_ortho(alphabar, damp)
+
+        # Use a plane rotation (Q_i) to turn B_i to R_i
+
+        rhoold = rho
+        c, s, rho = _sym_ortho(alphahat, beta)
+        thetanew = s*alpha
+        alphabar = c*alpha
+
+        # Use a plane rotation (Qbar_i) to turn R_i^T to R_i^bar
+
+        rhobarold = rhobar
+        zetaold = zeta
+        thetabar = sbar * rho
+        rhotemp = cbar * rho
+        cbar, sbar, rhobar = _sym_ortho(cbar * rho, thetanew)
+        zeta = cbar * zetabar
+        zetabar = - sbar * zetabar
+
+        # Update h, h_hat, x.
+
+        hbar *= - (thetabar * rho / (rhoold * rhobarold))
+        hbar += h
+        x += (zeta / (rho * rhobar)) * hbar
+        h *= - (thetanew / rho)
+        h += v
+
+        # Estimate of ||r||.
+
+        # Apply rotation Qhat_{k,2k+1}.
+        betaacute = chat * betadd
+        betacheck = -shat * betadd
+
+        # Apply rotation Q_{k,k+1}.
+        betahat = c * betaacute
+        betadd = -s * betaacute
+
+        # Apply rotation Qtilde_{k-1}.
+        # betad = betad_{k-1} here.
+
+        thetatildeold = thetatilde
+        ctildeold, stildeold, rhotildeold = _sym_ortho(rhodold, thetabar)
+        thetatilde = stildeold * rhobar
+        rhodold = ctildeold * rhobar
+        betad = - stildeold * betad + ctildeold * betahat
+
+        # betad   = betad_k here.
+        # rhodold = rhod_k  here.
+
+        tautildeold = (zetaold - thetatildeold * tautildeold) / rhotildeold
+        taud = (zeta - thetatilde * tautildeold) / rhodold
+        d = d + betacheck * betacheck
+        normr = sqrt(d + (betad - taud)**2 + betadd * betadd)
+
+        # Estimate ||A||.
+        normA2 = normA2 + beta * beta
+        normA = sqrt(normA2)
+        normA2 = normA2 + alpha * alpha
+
+        # Estimate cond(A).
+        maxrbar = max(maxrbar, rhobarold)
+        if itn > 1:
+            minrbar = min(minrbar, rhobarold)
+        condA = max(maxrbar, rhotemp) / min(minrbar, rhotemp)
+
+        # Test for convergence.
+
+        # Compute norms for convergence testing.
+        normar = abs(zetabar)
+        normx = norm(x)
+
+        # Now use these norms to estimate certain other quantities,
+        # some of which will be small near a solution.
+
+        test1 = normr / normb
+        if (normA * normr) != 0:
+            test2 = normar / (normA * normr)
+        else:
+            test2 = inf
+        test3 = 1 / condA
+        t1 = test1 / (1 + normA * normx / normb)
+        rtol = btol + atol * normA * normx / normb
+
+        # The following tests guard against extremely small values of
+        # atol, btol or ctol.  (The user may have set any or all of
+        # the parameters atol, btol, conlim  to 0.)
+        # The effect is equivalent to the normAl tests using
+        # atol = eps,  btol = eps,  conlim = 1/eps.
+
+        if itn >= maxiter:
+            istop = 7
+        if 1 + test3 <= 1:
+            istop = 6
+        if 1 + test2 <= 1:
+            istop = 5
+        if 1 + t1 <= 1:
+            istop = 4
+
+        # Allow for tolerances set by the user.
+
+        if test3 <= ctol:
+            istop = 3
+        if test2 <= atol:
+            istop = 2
+        if test1 <= rtol:
+            istop = 1
+
+        # See if it is time to print something.
+
+        if show:
+            if (n <= 40) or (itn <= 10) or (itn >= maxiter - 10) or \
+               (itn % 10 == 0) or (test3 <= 1.1 * ctol) or \
+               (test2 <= 1.1 * atol) or (test1 <= 1.1 * rtol) or \
+               (istop != 0):
+
+                if pcount >= pfreq:
+                    pcount = 0
+                    print(' ')
+                    print(hdg1, hdg2)
+                pcount = pcount + 1
+                str1 = f'{itn:6g} {x[0]:12.5e}'
+                str2 = f' {normr:10.3e} {normar:10.3e}'
+                str3 = f'  {test1:8.1e} {test2:8.1e}'
+                str4 = f' {normA:8.1e} {condA:8.1e}'
+                print(''.join([str1, str2, str3, str4]))
+
+        if istop > 0:
+            break
+
+    # Print the stopping condition.
+
+    if show:
+        print(' ')
+        print('LSMR finished')
+        print(msg[istop])
+        print(f'istop ={istop:8g}    normr ={normr:8.1e}')
+        print(f'    normA ={normA:8.1e}    normAr ={normar:8.1e}')
+        print(f'itn   ={itn:8g}    condA ={condA:8.1e}')
+        print('    normx =%8.1e' % (normx))
+        print(str1, str2)
+        print(str3, str4)
+
+    return x, istop, itn, normr, normar, normA, condA, normx

.CondaPkg/env/Lib/site-packages/scipy/sparse/linalg/_isolve/lsqr.py

@@ -0,0 +1,587 @@
+"""Sparse Equations and Least Squares.
+
+The original Fortran code was written by C. C. Paige and M. A. Saunders as
+described in
+
+C. C. Paige and M. A. Saunders, LSQR: An algorithm for sparse linear
+equations and sparse least squares, TOMS 8(1), 43--71 (1982).
+
+C. C. Paige and M. A. Saunders, Algorithm 583; LSQR: Sparse linear
+equations and least-squares problems, TOMS 8(2), 195--209 (1982).
+
+It is licensed under the following BSD license:
+
+Copyright (c) 2006, Systems Optimization Laboratory
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+
+    * Neither the name of Stanford University nor the names of its
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+The Fortran code was translated to Python for use in CVXOPT by Jeffery
+Kline with contributions by Mridul Aanjaneya and Bob Myhill.
+
+Adapted for SciPy by Stefan van der Walt.
+
+"""
+
+__all__ = ['lsqr']
+
+import numpy as np
+from math import sqrt
+from scipy.sparse.linalg._interface import aslinearoperator
+
+eps = np.finfo(np.float64).eps
+
+
+def _sym_ortho(a, b):
+    """
+    Stable implementation of Givens rotation.
+
+    Notes
+    -----
+    The routine 'SymOrtho' was added for numerical stability. This is
+    recommended by S.-C. Choi in [1]_.  It removes the unpleasant potential of
+    ``1/eps`` in some important places (see, for example text following
+    "Compute the next plane rotation Qk" in minres.py).
+
+    References
+    ----------
+    .. [1] S.-C. Choi, "Iterative Methods for Singular Linear Equations
+           and Least-Squares Problems", Dissertation,
+           http://www.stanford.edu/group/SOL/dissertations/sou-cheng-choi-thesis.pdf
+
+    """
+    if b == 0:
+        return np.sign(a), 0, abs(a)
+    elif a == 0:
+        return 0, np.sign(b), abs(b)
+    elif abs(b) > abs(a):
+        tau = a / b
+        s = np.sign(b) / sqrt(1 + tau * tau)
+        c = s * tau
+        r = b / s
+    else:
+        tau = b / a
+        c = np.sign(a) / sqrt(1+tau*tau)
+        s = c * tau
+        r = a / c
+    return c, s, r
+
+
+def lsqr(A, b, damp=0.0, atol=1e-6, btol=1e-6, conlim=1e8,
+         iter_lim=None, show=False, calc_var=False, x0=None):
+    """Find the least-squares solution to a large, sparse, linear system
+    of equations.
+
+    The function solves ``Ax = b``  or  ``min ||Ax - b||^2`` or
+    ``min ||Ax - b||^2 + d^2 ||x - x0||^2``.
+
+    The matrix A may be square or rectangular (over-determined or
+    under-determined), and may have any rank.
+
+    ::
+
+      1. Unsymmetric equations --    solve  Ax = b
+
+      2. Linear least squares  --    solve  Ax = b
+                                     in the least-squares sense
+
+      3. Damped least squares  --    solve  (   A    )*x = (    b    )
+                                            ( damp*I )     ( damp*x0 )
+                                     in the least-squares sense
+
+    Parameters
+    ----------
+    A : {sparse matrix, ndarray, LinearOperator}
+        Representation of an m-by-n matrix.
+        Alternatively, ``A`` can be a linear operator which can
+        produce ``Ax`` and ``A^T x`` using, e.g.,
+        ``scipy.sparse.linalg.LinearOperator``.
+    b : array_like, shape (m,)
+        Right-hand side vector ``b``.
+    damp : float
+        Damping coefficient. Default is 0.
+    atol, btol : float, optional
+        Stopping tolerances. `lsqr` continues iterations until a
+        certain backward error estimate is smaller than some quantity
+        depending on atol and btol.  Let ``r = b - Ax`` be the
+        residual vector for the current approximate solution ``x``.
+        If ``Ax = b`` seems to be consistent, `lsqr` terminates
+        when ``norm(r) <= atol * norm(A) * norm(x) + btol * norm(b)``.
+        Otherwise, `lsqr` terminates when ``norm(A^H r) <=
+        atol * norm(A) * norm(r)``.  If both tolerances are 1.0e-6 (default),
+        the final ``norm(r)`` should be accurate to about 6
+        digits. (The final ``x`` will usually have fewer correct digits,
+        depending on ``cond(A)`` and the size of LAMBDA.)  If `atol`
+        or `btol` is None, a default value of 1.0e-6 will be used.
+        Ideally, they should be estimates of the relative error in the
+        entries of ``A`` and ``b`` respectively.  For example, if the entries
+        of ``A`` have 7 correct digits, set ``atol = 1e-7``. This prevents
+        the algorithm from doing unnecessary work beyond the
+        uncertainty of the input data.
+    conlim : float, optional
+        Another stopping tolerance.  lsqr terminates if an estimate of
+        ``cond(A)`` exceeds `conlim`.  For compatible systems ``Ax =
+        b``, `conlim` could be as large as 1.0e+12 (say).  For
+        least-squares problems, conlim should be less than 1.0e+8.
+        Maximum precision can be obtained by setting ``atol = btol =
+        conlim = zero``, but the number of iterations may then be
+        excessive. Default is 1e8.
+    iter_lim : int, optional
+        Explicit limitation on number of iterations (for safety).
+    show : bool, optional
+        Display an iteration log. Default is False.
+    calc_var : bool, optional
+        Whether to estimate diagonals of ``(A'A + damp^2*I)^{-1}``.
+    x0 : array_like, shape (n,), optional
+        Initial guess of x, if None zeros are used. Default is None.
+
+        .. versionadded:: 1.0.0
+
+    Returns
+    -------
+    x : ndarray of float
+        The final solution.
+    istop : int
+        Gives the reason for termination.
+        1 means x is an approximate solution to Ax = b.
+        2 means x approximately solves the least-squares problem.
+    itn : int
+        Iteration number upon termination.
+    r1norm : float
+        ``norm(r)``, where ``r = b - Ax``.
+    r2norm : float
+        ``sqrt( norm(r)^2  +  damp^2 * norm(x - x0)^2 )``.  Equal to `r1norm`
+        if ``damp == 0``.
+    anorm : float
+        Estimate of Frobenius norm of ``Abar = [[A]; [damp*I]]``.
+    acond : float
+        Estimate of ``cond(Abar)``.
+    arnorm : float
+        Estimate of ``norm(A'@r - damp^2*(x - x0))``.
+    xnorm : float
+        ``norm(x)``
+    var : ndarray of float
+        If ``calc_var`` is True, estimates all diagonals of
+        ``(A'A)^{-1}`` (if ``damp == 0``) or more generally ``(A'A +
+        damp^2*I)^{-1}``.  This is well defined if A has full column
+        rank or ``damp > 0``.  (Not sure what var means if ``rank(A)
+        < n`` and ``damp = 0.``)
+
+    Notes
+    -----
+    LSQR uses an iterative method to approximate the solution.  The
+    number of iterations required to reach a certain accuracy depends
+    strongly on the scaling of the problem.  Poor scaling of the rows
+    or columns of A should therefore be avoided where possible.
+
+    For example, in problem 1 the solution is unaltered by
+    row-scaling.  If a row of A is very small or large compared to
+    the other rows of A, the corresponding row of ( A  b ) should be
+    scaled up or down.
+
+    In problems 1 and 2, the solution x is easily recovered
+    following column-scaling.  Unless better information is known,
+    the nonzero columns of A should be scaled so that they all have
+    the same Euclidean norm (e.g., 1.0).
+
+    In problem 3, there is no freedom to re-scale if damp is
+    nonzero.  However, the value of damp should be assigned only
+    after attention has been paid to the scaling of A.
+
+    The parameter damp is intended to help regularize
+    ill-conditioned systems, by preventing the true solution from
+    being very large.  Another aid to regularization is provided by
+    the parameter acond, which may be used to terminate iterations
+    before the computed solution becomes very large.
+
+    If some initial estimate ``x0`` is known and if ``damp == 0``,
+    one could proceed as follows:
+
+      1. Compute a residual vector ``r0 = b - A@x0``.
+      2. Use LSQR to solve the system  ``A@dx = r0``.
+      3. Add the correction dx to obtain a final solution ``x = x0 + dx``.
+
+    This requires that ``x0`` be available before and after the call
+    to LSQR.  To judge the benefits, suppose LSQR takes k1 iterations
+    to solve A@x = b and k2 iterations to solve A@dx = r0.
+    If x0 is "good", norm(r0) will be smaller than norm(b).
+    If the same stopping tolerances atol and btol are used for each
+    system, k1 and k2 will be similar, but the final solution x0 + dx
+    should be more accurate.  The only way to reduce the total work
+    is to use a larger stopping tolerance for the second system.
+    If some value btol is suitable for A@x = b, the larger value
+    btol*norm(b)/norm(r0)  should be suitable for A@dx = r0.
+
+    Preconditioning is another way to reduce the number of iterations.
+    If it is possible to solve a related system ``M@x = b``
+    efficiently, where M approximates A in some helpful way (e.g. M -
+    A has low rank or its elements are small relative to those of A),
+    LSQR may converge more rapidly on the system ``A@M(inverse)@z =
+    b``, after which x can be recovered by solving M@x = z.
+
+    If A is symmetric, LSQR should not be used!
+
+    Alternatives are the symmetric conjugate-gradient method (cg)
+    and/or SYMMLQ.  SYMMLQ is an implementation of symmetric cg that
+    applies to any symmetric A and will converge more rapidly than
+    LSQR.  If A is positive definite, there are other implementations
+    of symmetric cg that require slightly less work per iteration than
+    SYMMLQ (but will take the same number of iterations).
+
+    References
+    ----------
+    .. [1] C. C. Paige and M. A. Saunders (1982a).
+           "LSQR: An algorithm for sparse linear equations and
+           sparse least squares", ACM TOMS 8(1), 43-71.
+    .. [2] C. C. Paige and M. A. Saunders (1982b).
+           "Algorithm 583.  LSQR: Sparse linear equations and least
+           squares problems", ACM TOMS 8(2), 195-209.
+    .. [3] M. A. Saunders (1995).  "Solution of sparse rectangular
+           systems using LSQR and CRAIG", BIT 35, 588-604.
+
+    Examples
+    --------
+    >>> import numpy as np
+    >>> from scipy.sparse import csc_matrix
+    >>> from scipy.sparse.linalg import lsqr
+    >>> A = csc_matrix([[1., 0.], [1., 1.], [0., 1.]], dtype=float)
+
+    The first example has the trivial solution ``[0, 0]``
+
+    >>> b = np.array([0., 0., 0.], dtype=float)
+    >>> x, istop, itn, normr = lsqr(A, b)[:4]
+    >>> istop
+    0
+    >>> x
+    array([ 0.,  0.])
+
+    The stopping code `istop=0` returned indicates that a vector of zeros was
+    found as a solution. The returned solution `x` indeed contains
+    ``[0., 0.]``. The next example has a non-trivial solution:
+
+    >>> b = np.array([1., 0., -1.], dtype=float)
+    >>> x, istop, itn, r1norm = lsqr(A, b)[:4]
+    >>> istop
+    1
+    >>> x
+    array([ 1., -1.])
+    >>> itn
+    1
+    >>> r1norm
+    4.440892098500627e-16
+
+    As indicated by `istop=1`, `lsqr` found a solution obeying the tolerance
+    limits. The given solution ``[1., -1.]`` obviously solves the equation. The
+    remaining return values include information about the number of iterations
+    (`itn=1`) and the remaining difference of left and right side of the solved
+    equation.
+    The final example demonstrates the behavior in the case where there is no
+    solution for the equation:
+
+    >>> b = np.array([1., 0.01, -1.], dtype=float)
+    >>> x, istop, itn, r1norm = lsqr(A, b)[:4]
+    >>> istop
+    2
+    >>> x
+    array([ 1.00333333, -0.99666667])
+    >>> A.dot(x)-b
+    array([ 0.00333333, -0.00333333,  0.00333333])
+    >>> r1norm
+    0.005773502691896255
+
+    `istop` indicates that the system is inconsistent and thus `x` is rather an
+    approximate solution to the corresponding least-squares problem. `r1norm`
+    contains the norm of the minimal residual that was found.
+    """
+    A = aslinearoperator(A)
+    b = np.atleast_1d(b)
+    if b.ndim > 1:
+        b = b.squeeze()
+
+    m, n = A.shape
+    if iter_lim is None:
+        iter_lim = 2 * n
+    var = np.zeros(n)
+
+    msg = ('The exact solution is  x = 0                              ',
+           'Ax - b is small enough, given atol, btol                  ',
+           'The least-squares solution is good enough, given atol     ',
+           'The estimate of cond(Abar) has exceeded conlim            ',
+           'Ax - b is small enough for this machine                   ',
+           'The least-squares solution is good enough for this machine',
+           'Cond(Abar) seems to be too large for this machine         ',
+           'The iteration limit has been reached                      ')
+
+    if show:
+        print(' ')
+        print('LSQR            Least-squares solution of  Ax = b')
+        str1 = f'The matrix A has {m} rows and {n} columns'
+        str2 = f'damp = {damp:20.14e}   calc_var = {calc_var:8g}'
+        str3 = f'atol = {atol:8.2e}                 conlim = {conlim:8.2e}'
+        str4 = f'btol = {btol:8.2e}               iter_lim = {iter_lim:8g}'
+        print(str1)
+        print(str2)
+        print(str3)
+        print(str4)
+
+    itn = 0
+    istop = 0
+    ctol = 0
+    if conlim > 0:
+        ctol = 1/conlim
+    anorm = 0
+    acond = 0
+    dampsq = damp**2
+    ddnorm = 0
+    res2 = 0
+    xnorm = 0
+    xxnorm = 0
+    z = 0
+    cs2 = -1
+    sn2 = 0
+
+    # Set up the first vectors u and v for the bidiagonalization.
+    # These satisfy  beta*u = b - A@x,  alfa*v = A'@u.
+    u = b
+    bnorm = np.linalg.norm(b)
+
+    if x0 is None:
+        x = np.zeros(n)
+        beta = bnorm.copy()
+    else:
+        x = np.asarray(x0)
+        u = u - A.matvec(x)
+        beta = np.linalg.norm(u)
+
+    if beta > 0:
+        u = (1/beta) * u
+        v = A.rmatvec(u)
+        alfa = np.linalg.norm(v)
+    else:
+        v = x.copy()
+        alfa = 0
+
+    if alfa > 0:
+        v = (1/alfa) * v
+    w = v.copy()
+
+    rhobar = alfa
+    phibar = beta
+    rnorm = beta
+    r1norm = rnorm
+    r2norm = rnorm
+
+    # Reverse the order here from the original matlab code because
+    # there was an error on return when arnorm==0
+    arnorm = alfa * beta
+    if arnorm == 0:
+        if show:
+            print(msg[0])
+        return x, istop, itn, r1norm, r2norm, anorm, acond, arnorm, xnorm, var
+
+    head1 = '   Itn      x[0]       r1norm     r2norm '
+    head2 = ' Compatible    LS      Norm A   Cond A'
+
+    if show:
+        print(' ')
+        print(head1, head2)
+        test1 = 1
+        test2 = alfa / beta
+        str1 = f'{itn:6g} {x[0]:12.5e}'
+        str2 = f' {r1norm:10.3e} {r2norm:10.3e}'
+        str3 = f'  {test1:8.1e} {test2:8.1e}'
+        print(str1, str2, str3)
+
+    # Main iteration loop.
+    while itn < iter_lim:
+        itn = itn + 1
+        # Perform the next step of the bidiagonalization to obtain the
+        # next  beta, u, alfa, v. These satisfy the relations
+        #     beta*u  =  a@v   -  alfa*u,
+        #     alfa*v  =  A'@u  -  beta*v.
+        u = A.matvec(v) - alfa * u
+        beta = np.linalg.norm(u)
+
+        if beta > 0:
+            u = (1/beta) * u
+            anorm = sqrt(anorm**2 + alfa**2 + beta**2 + dampsq)
+            v = A.rmatvec(u) - beta * v
+            alfa = np.linalg.norm(v)
+            if alfa > 0:
+                v = (1 / alfa) * v
+
+        # Use a plane rotation to eliminate the damping parameter.
+        # This alters the diagonal (rhobar) of the lower-bidiagonal matrix.
+        if damp > 0:
+            rhobar1 = sqrt(rhobar**2 + dampsq)
+            cs1 = rhobar / rhobar1
+            sn1 = damp / rhobar1
+            psi = sn1 * phibar
+            phibar = cs1 * phibar
+        else:
+            # cs1 = 1 and sn1 = 0
+            rhobar1 = rhobar
+            psi = 0.
+
+        # Use a plane rotation to eliminate the subdiagonal element (beta)
+        # of the lower-bidiagonal matrix, giving an upper-bidiagonal matrix.
+        cs, sn, rho = _sym_ortho(rhobar1, beta)
+
+        theta = sn * alfa
+        rhobar = -cs * alfa
+        phi = cs * phibar
+        phibar = sn * phibar
+        tau = sn * phi
+
+        # Update x and w.
+        t1 = phi / rho
+        t2 = -theta / rho
+        dk = (1 / rho) * w
+
+        x = x + t1 * w
+        w = v + t2 * w
+        ddnorm = ddnorm + np.linalg.norm(dk)**2
+
+        if calc_var:
+            var = var + dk**2
+
+        # Use a plane rotation on the right to eliminate the
+        # super-diagonal element (theta) of the upper-bidiagonal matrix.
+        # Then use the result to estimate norm(x).
+        delta = sn2 * rho
+        gambar = -cs2 * rho
+        rhs = phi - delta * z
+        zbar = rhs / gambar
+        xnorm = sqrt(xxnorm + zbar**2)
+        gamma = sqrt(gambar**2 + theta**2)
+        cs2 = gambar / gamma
+        sn2 = theta / gamma
+        z = rhs / gamma
+        xxnorm = xxnorm + z**2
+
+        # Test for convergence.
+        # First, estimate the condition of the matrix  Abar,
+        # and the norms of  rbar  and  Abar'rbar.
+        acond = anorm * sqrt(ddnorm)
+        res1 = phibar**2
+        res2 = res2 + psi**2
+        rnorm = sqrt(res1 + res2)
+        arnorm = alfa * abs(tau)
+
+        # Distinguish between
+        #    r1norm = ||b - Ax|| and
+        #    r2norm = rnorm in current code
+        #           = sqrt(r1norm^2 + damp^2*||x - x0||^2).
+        #    Estimate r1norm from
+        #    r1norm = sqrt(r2norm^2 - damp^2*||x - x0||^2).
+        # Although there is cancellation, it might be accurate enough.
+        if damp > 0:
+            r1sq = rnorm**2 - dampsq * xxnorm
+            r1norm = sqrt(abs(r1sq))
+            if r1sq < 0:
+                r1norm = -r1norm
+        else:
+            r1norm = rnorm
+        r2norm = rnorm
+
+        # Now use these norms to estimate certain other quantities,
+        # some of which will be small near a solution.
+        test1 = rnorm / bnorm
+        test2 = arnorm / (anorm * rnorm + eps)
+        test3 = 1 / (acond + eps)
+        t1 = test1 / (1 + anorm * xnorm / bnorm)
+        rtol = btol + atol * anorm * xnorm / bnorm
+
+        # The following tests guard against extremely small values of
+        # atol, btol  or  ctol.  (The user may have set any or all of
+        # the parameters  atol, btol, conlim  to 0.)
+        # The effect is equivalent to the normal tests using
+        # atol = eps,  btol = eps,  conlim = 1/eps.
+        if itn >= iter_lim:
+            istop = 7
+        if 1 + test3 <= 1:
+            istop = 6
+        if 1 + test2 <= 1:
+            istop = 5
+        if 1 + t1 <= 1:
+            istop = 4
+
+        # Allow for tolerances set by the user.
+        if test3 <= ctol:
+            istop = 3
+        if test2 <= atol:
+            istop = 2
+        if test1 <= rtol:
+            istop = 1
+
+        if show:
+            # See if it is time to print something.
+            prnt = False
+            if n <= 40:
+                prnt = True
+            if itn <= 10:
+                prnt = True
+            if itn >= iter_lim-10:
+                prnt = True
+            # if itn%10 == 0: prnt = True
+            if test3 <= 2*ctol:
+                prnt = True
+            if test2 <= 10*atol:
+                prnt = True
+            if test1 <= 10*rtol:
+                prnt = True
+            if istop != 0:
+                prnt = True
+
+            if prnt:
+                str1 = f'{itn:6g} {x[0]:12.5e}'
+                str2 = f' {r1norm:10.3e} {r2norm:10.3e}'
+                str3 = f'  {test1:8.1e} {test2:8.1e}'
+                str4 = f' {anorm:8.1e} {acond:8.1e}'
+                print(str1, str2, str3, str4)
+
+        if istop != 0:
+            break
+
+    # End of iteration loop.
+    # Print the stopping condition.
+    if show:
+        print(' ')
+        print('LSQR finished')
+        print(msg[istop])
+        print(' ')
+        str1 = f'istop ={istop:8g}   r1norm ={r1norm:8.1e}'
+        str2 = f'anorm ={anorm:8.1e}   arnorm ={arnorm:8.1e}'
+        str3 = f'itn   ={itn:8g}   r2norm ={r2norm:8.1e}'
+        str4 = f'acond ={acond:8.1e}   xnorm  ={xnorm:8.1e}'
+        print(str1 + '   ' + str2)
+        print(str3 + '   ' + str4)
+        print(' ')
+
+    return x, istop, itn, r1norm, r2norm, anorm, acond, arnorm, xnorm, var

.CondaPkg/env/Lib/site-packages/scipy/sparse/linalg/_isolve/minres.py

@@ -0,0 +1,372 @@
+from numpy import inner, zeros, inf, finfo
+from numpy.linalg import norm
+from math import sqrt
+
+from .utils import make_system
+
+__all__ = ['minres']
+
+
+def minres(A, b, x0=None, *, rtol=1e-5, shift=0.0, maxiter=None,
+           M=None, callback=None, show=False, check=False):
+    """
+    Use MINimum RESidual iteration to solve Ax=b
+
+    MINRES minimizes norm(Ax - b) for a real symmetric matrix A.  Unlike
+    the Conjugate Gradient method, A can be indefinite or singular.
+
+    If shift != 0 then the method solves (A - shift*I)x = b
+
+    Parameters
+    ----------
+    A : {sparse matrix, ndarray, LinearOperator}
+        The real symmetric N-by-N matrix of the linear system
+        Alternatively, ``A`` can be a linear operator which can
+        produce ``Ax`` using, e.g.,
+        ``scipy.sparse.linalg.LinearOperator``.
+    b : ndarray
+        Right hand side of the linear system. Has shape (N,) or (N,1).
+
+    Returns
+    -------
+    x : ndarray
+        The converged solution.
+    info : integer
+        Provides convergence information:
+            0  : successful exit
+            >0 : convergence to tolerance not achieved, number of iterations
+            <0 : illegal input or breakdown
+
+    Other Parameters
+    ----------------
+    x0 : ndarray
+        Starting guess for the solution.
+    shift : float
+        Value to apply to the system ``(A - shift * I)x = b``. Default is 0.
+    rtol : float
+        Tolerance to achieve. The algorithm terminates when the relative
+        residual is below ``rtol``.
+    maxiter : integer
+        Maximum number of iterations.  Iteration will stop after maxiter
+        steps even if the specified tolerance has not been achieved.
+    M : {sparse matrix, ndarray, LinearOperator}
+        Preconditioner for A.  The preconditioner should approximate the
+        inverse of A.  Effective preconditioning dramatically improves the
+        rate of convergence, which implies that fewer iterations are needed
+        to reach a given error tolerance.
+    callback : function
+        User-supplied function to call after each iteration.  It is called
+        as callback(xk), where xk is the current solution vector.
+    show : bool
+        If ``True``, print out a summary and metrics related to the solution
+        during iterations. Default is ``False``.
+    check : bool
+        If ``True``, run additional input validation to check that `A` and
+        `M` (if specified) are symmetric. Default is ``False``.
+
+    Examples
+    --------
+    >>> import numpy as np
+    >>> from scipy.sparse import csc_matrix
+    >>> from scipy.sparse.linalg import minres
+    >>> A = csc_matrix([[3, 2, 0], [1, -1, 0], [0, 5, 1]], dtype=float)
+    >>> A = A + A.T
+    >>> b = np.array([2, 4, -1], dtype=float)
+    >>> x, exitCode = minres(A, b)
+    >>> print(exitCode)            # 0 indicates successful convergence
+    0
+    >>> np.allclose(A.dot(x), b)
+    True
+
+    References
+    ----------
+    Solution of sparse indefinite systems of linear equations,
+        C. C. Paige and M. A. Saunders (1975),
+        SIAM J. Numer. Anal. 12(4), pp. 617-629.
+        https://web.stanford.edu/group/SOL/software/minres/
+
+    This file is a translation of the following MATLAB implementation:
+        https://web.stanford.edu/group/SOL/software/minres/minres-matlab.zip
+
+    """
+    A, M, x, b, postprocess = make_system(A, M, x0, b)
+
+    matvec = A.matvec
+    psolve = M.matvec
+
+    first = 'Enter minres.   '
+    last = 'Exit  minres.   '
+
+    n = A.shape[0]
+
+    if maxiter is None:
+        maxiter = 5 * n
+
+    msg = [' beta2 = 0.  If M = I, b and x are eigenvectors    ',   # -1
+            ' beta1 = 0.  The exact solution is x0          ',   # 0
+            ' A solution to Ax = b was found, given rtol        ',   # 1
+            ' A least-squares solution was found, given rtol    ',   # 2
+            ' Reasonable accuracy achieved, given eps           ',   # 3
+            ' x has converged to an eigenvector                 ',   # 4
+            ' acond has exceeded 0.1/eps                        ',   # 5
+            ' The iteration limit was reached                   ',   # 6
+            ' A  does not define a symmetric matrix             ',   # 7
+            ' M  does not define a symmetric matrix             ',   # 8
+            ' M  does not define a pos-def preconditioner       ']   # 9
+
+    if show:
+        print(first + 'Solution of symmetric Ax = b')
+        print(first + f'n      =  {n:3g}     shift  =  {shift:23.14e}')
+        print(first + f'itnlim =  {maxiter:3g}     rtol   =  {rtol:11.2e}')
+        print()
+
+    istop = 0
+    itn = 0
+    Anorm = 0
+    Acond = 0
+    rnorm = 0
+    ynorm = 0
+
+    xtype = x.dtype
+
+    eps = finfo(xtype).eps
+
+    # Set up y and v for the first Lanczos vector v1.
+    # y  =  beta1 P' v1,  where  P = C**(-1).
+    # v is really P' v1.
+
+    if x0 is None:
+        r1 = b.copy()
+    else:
+        r1 = b - A@x
+    y = psolve(r1)
+
+    beta1 = inner(r1, y)
+
+    if beta1 < 0:
+        raise ValueError('indefinite preconditioner')
+    elif beta1 == 0:
+        return (postprocess(x), 0)
+
+    bnorm = norm(b)
+    if bnorm == 0:
+        x = b
+        return (postprocess(x), 0)
+
+    beta1 = sqrt(beta1)
+
+    if check:
+        # are these too strict?
+
+        # see if A is symmetric
+        w = matvec(y)
+        r2 = matvec(w)
+        s = inner(w,w)
+        t = inner(y,r2)
+        z = abs(s - t)
+        epsa = (s + eps) * eps**(1.0/3.0)
+        if z > epsa:
+            raise ValueError('non-symmetric matrix')
+
+        # see if M is symmetric
+        r2 = psolve(y)
+        s = inner(y,y)
+        t = inner(r1,r2)
+        z = abs(s - t)
+        epsa = (s + eps) * eps**(1.0/3.0)
+        if z > epsa:
+            raise ValueError('non-symmetric preconditioner')
+
+    # Initialize other quantities
+    oldb = 0
+    beta = beta1
+    dbar = 0
+    epsln = 0
+    qrnorm = beta1
+    phibar = beta1
+    rhs1 = beta1
+    rhs2 = 0
+    tnorm2 = 0
+    gmax = 0
+    gmin = finfo(xtype).max
+    cs = -1
+    sn = 0
+    w = zeros(n, dtype=xtype)
+    w2 = zeros(n, dtype=xtype)
+    r2 = r1
+
+    if show:
+        print()
+        print()
+        print('   Itn     x(1)     Compatible    LS       norm(A)  cond(A) gbar/|A|')
+
+    while itn < maxiter:
+        itn += 1
+
+        s = 1.0/beta
+        v = s*y
+
+        y = matvec(v)
+        y = y - shift * v
+
+        if itn >= 2:
+            y = y - (beta/oldb)*r1
+
+        alfa = inner(v,y)
+        y = y - (alfa/beta)*r2
+        r1 = r2
+        r2 = y
+        y = psolve(r2)
+        oldb = beta
+        beta = inner(r2,y)
+        if beta < 0:
+            raise ValueError('non-symmetric matrix')
+        beta = sqrt(beta)
+        tnorm2 += alfa**2 + oldb**2 + beta**2
+
+        if itn == 1:
+            if beta/beta1 <= 10*eps:
+                istop = -1  # Terminate later
+
+        # Apply previous rotation Qk-1 to get
+        #   [deltak epslnk+1] = [cs  sn][dbark    0   ]
+        #   [gbar k dbar k+1]   [sn -cs][alfak betak+1].
+
+        oldeps = epsln
+        delta = cs * dbar + sn * alfa   # delta1 = 0         deltak
+        gbar = sn * dbar - cs * alfa   # gbar 1 = alfa1     gbar k
+        epsln = sn * beta     # epsln2 = 0         epslnk+1
+        dbar = - cs * beta   # dbar 2 = beta2     dbar k+1
+        root = norm([gbar, dbar])
+        Arnorm = phibar * root
+
+        # Compute the next plane rotation Qk
+
+        gamma = norm([gbar, beta])       # gammak
+        gamma = max(gamma, eps)
+        cs = gbar / gamma             # ck
+        sn = beta / gamma             # sk
+        phi = cs * phibar              # phik
+        phibar = sn * phibar              # phibark+1
+
+        # Update  x.
+
+        denom = 1.0/gamma
+        w1 = w2
+        w2 = w
+        w = (v - oldeps*w1 - delta*w2) * denom
+        x = x + phi*w
+
+        # Go round again.
+
+        gmax = max(gmax, gamma)
+        gmin = min(gmin, gamma)
+        z = rhs1 / gamma
+        rhs1 = rhs2 - delta*z
+        rhs2 = - epsln*z
+
+        # Estimate various norms and test for convergence.
+
+        Anorm = sqrt(tnorm2)
+        ynorm = norm(x)
+        epsa = Anorm * eps
+        epsx = Anorm * ynorm * eps
+        epsr = Anorm * ynorm * rtol
+        diag = gbar
+
+        if diag == 0:
+            diag = epsa
+
+        qrnorm = phibar
+        rnorm = qrnorm
+        if ynorm == 0 or Anorm == 0:
+            test1 = inf
+        else:
+            test1 = rnorm / (Anorm*ynorm)    # ||r||  / (||A|| ||x||)
+        if Anorm == 0:
+            test2 = inf
+        else:
+            test2 = root / Anorm            # ||Ar|| / (||A|| ||r||)
+
+        # Estimate  cond(A).
+        # In this version we look at the diagonals of  R  in the
+        # factorization of the lower Hessenberg matrix,  Q @ H = R,
+        # where H is the tridiagonal matrix from Lanczos with one
+        # extra row, beta(k+1) e_k^T.
+
+        Acond = gmax/gmin
+
+        # See if any of the stopping criteria are satisfied.
+        # In rare cases, istop is already -1 from above (Abar = const*I).
+
+        if istop == 0:
+            t1 = 1 + test1      # These tests work if rtol < eps
+            t2 = 1 + test2
+            if t2 <= 1:
+                istop = 2
+            if t1 <= 1:
+                istop = 1
+
+            if itn >= maxiter:
+                istop = 6
+            if Acond >= 0.1/eps:
+                istop = 4
+            if epsx >= beta1:
+                istop = 3
+            # if rnorm <= epsx   : istop = 2
+            # if rnorm <= epsr   : istop = 1
+            if test2 <= rtol:
+                istop = 2
+            if test1 <= rtol:
+                istop = 1
+
+        # See if it is time to print something.
+
+        prnt = False
+        if n <= 40:
+            prnt = True
+        if itn <= 10:
+            prnt = True
+        if itn >= maxiter-10:
+            prnt = True
+        if itn % 10 == 0:
+            prnt = True
+        if qrnorm <= 10*epsx:
+            prnt = True
+        if qrnorm <= 10*epsr:
+            prnt = True
+        if Acond <= 1e-2/eps:
+            prnt = True
+        if istop != 0:
+            prnt = True
+
+        if show and prnt:
+            str1 = f'{itn:6g} {x[0]:12.5e} {test1:10.3e}'
+            str2 = f' {test2:10.3e}'
+            str3 = f' {Anorm:8.1e} {Acond:8.1e} {gbar/Anorm:8.1e}'
+
+            print(str1 + str2 + str3)
+
+            if itn % 10 == 0:
+                print()
+
+        if callback is not None:
+            callback(x)
+
+        if istop != 0:
+            break  # TODO check this
+
+    if show:
+        print()
+        print(last + f' istop   =  {istop:3g}               itn   ={itn:5g}')
+        print(last + f' Anorm   =  {Anorm:12.4e}      Acond =  {Acond:12.4e}')
+        print(last + f' rnorm   =  {rnorm:12.4e}      ynorm =  {ynorm:12.4e}')
+        print(last + f' Arnorm  =  {Arnorm:12.4e}')
+        print(last + msg[istop+1])
+
+    if istop == 6:
+        info = maxiter
+    else:
+        info = 0
+
+    return (postprocess(x),info)

.CondaPkg/env/Lib/site-packages/scipy/sparse/linalg/_isolve/tests/test_gcrotmk.py

@@ -0,0 +1,165 @@
+#!/usr/bin/env python
+"""Tests for the linalg._isolve.gcrotmk module
+"""
+
+from numpy.testing import (assert_, assert_allclose, assert_equal,
+                           suppress_warnings)
+
+import numpy as np
+from numpy import zeros, array, allclose
+from scipy.linalg import norm
+from scipy.sparse import csr_matrix, eye, rand
+
+from scipy.sparse.linalg._interface import LinearOperator
+from scipy.sparse.linalg import splu
+from scipy.sparse.linalg._isolve import gcrotmk, gmres
+
+
+Am = csr_matrix(array([[-2,1,0,0,0,9],
+                       [1,-2,1,0,5,0],
+                       [0,1,-2,1,0,0],
+                       [0,0,1,-2,1,0],
+                       [0,3,0,1,-2,1],
+                       [1,0,0,0,1,-2]]))
+b = array([1,2,3,4,5,6])
+count = [0]
+
+
+def matvec(v):
+    count[0] += 1
+    return Am@v
+
+
+A = LinearOperator(matvec=matvec, shape=Am.shape, dtype=Am.dtype)
+
+
+def do_solve(**kw):
+    count[0] = 0
+    with suppress_warnings() as sup:
+        sup.filter(DeprecationWarning, ".*called without specifying.*")
+        x0, flag = gcrotmk(A, b, x0=zeros(A.shape[0]), rtol=1e-14, **kw)
+    count_0 = count[0]
+    assert_(allclose(A@x0, b, rtol=1e-12, atol=1e-12), norm(A@x0-b))
+    return x0, count_0
+
+
+class TestGCROTMK:
+    def test_preconditioner(self):
+        # Check that preconditioning works
+        pc = splu(Am.tocsc())
+        M = LinearOperator(matvec=pc.solve, shape=A.shape, dtype=A.dtype)
+
+        x0, count_0 = do_solve()
+        x1, count_1 = do_solve(M=M)
+
+        assert_equal(count_1, 3)
+        assert_(count_1 < count_0/2)
+        assert_(allclose(x1, x0, rtol=1e-14))
+
+    def test_arnoldi(self):
+        np.random.seed(1)
+
+        A = eye(2000) + rand(2000, 2000, density=5e-4)
+        b = np.random.rand(2000)
+
+        # The inner arnoldi should be equivalent to gmres
+        with suppress_warnings() as sup:
+            sup.filter(DeprecationWarning, ".*called without specifying.*")
+            x0, flag0 = gcrotmk(A, b, x0=zeros(A.shape[0]), m=15, k=0, maxiter=1)
+            x1, flag1 = gmres(A, b, x0=zeros(A.shape[0]), restart=15, maxiter=1)
+
+        assert_equal(flag0, 1)
+        assert_equal(flag1, 1)
+        assert np.linalg.norm(A.dot(x0) - b) > 1e-3
+
+        assert_allclose(x0, x1)
+
+    def test_cornercase(self):
+        np.random.seed(1234)
+
+        # Rounding error may prevent convergence with tol=0 --- ensure
+        # that the return values in this case are correct, and no
+        # exceptions are raised
+
+        for n in [3, 5, 10, 100]:
+            A = 2*eye(n)
+
+            with suppress_warnings() as sup:
+                sup.filter(DeprecationWarning, ".*called without specifying.*")
+                b = np.ones(n)
+                x, info = gcrotmk(A, b, maxiter=10)
+                assert_equal(info, 0)
+                assert_allclose(A.dot(x) - b, 0, atol=1e-14)
+
+                x, info = gcrotmk(A, b, rtol=0, maxiter=10)
+                if info == 0:
+                    assert_allclose(A.dot(x) - b, 0, atol=1e-14)
+
+                b = np.random.rand(n)
+                x, info = gcrotmk(A, b, maxiter=10)
+                assert_equal(info, 0)
+                assert_allclose(A.dot(x) - b, 0, atol=1e-14)
+
+                x, info = gcrotmk(A, b, rtol=0, maxiter=10)
+                if info == 0:
+                    assert_allclose(A.dot(x) - b, 0, atol=1e-14)
+
+    def test_nans(self):
+        A = eye(3, format='lil')
+        A[1,1] = np.nan
+        b = np.ones(3)
+
+        with suppress_warnings() as sup:
+            sup.filter(DeprecationWarning, ".*called without specifying.*")
+            x, info = gcrotmk(A, b, rtol=0, maxiter=10)
+            assert_equal(info, 1)
+
+    def test_truncate(self):
+        np.random.seed(1234)
+        A = np.random.rand(30, 30) + np.eye(30)
+        b = np.random.rand(30)
+
+        for truncate in ['oldest', 'smallest']:
+            with suppress_warnings() as sup:
+                sup.filter(DeprecationWarning, ".*called without specifying.*")
+                x, info = gcrotmk(A, b, m=10, k=10, truncate=truncate,
+                                  rtol=1e-4, maxiter=200)
+            assert_equal(info, 0)
+            assert_allclose(A.dot(x) - b, 0, atol=1e-3)
+
+    def test_CU(self):
+        for discard_C in (True, False):
+            # Check that C,U behave as expected
+            CU = []
+            x0, count_0 = do_solve(CU=CU, discard_C=discard_C)
+            assert_(len(CU) > 0)
+            assert_(len(CU) <= 6)
+
+            if discard_C:
+                for c, u in CU:
+                    assert_(c is None)
+
+            # should converge immediately
+            x1, count_1 = do_solve(CU=CU, discard_C=discard_C)
+            if discard_C:
+                assert_equal(count_1, 2 + len(CU))
+            else:
+                assert_equal(count_1, 3)
+            assert_(count_1 <= count_0/2)
+            assert_allclose(x1, x0, atol=1e-14)
+
+    def test_denormals(self):
+        # Check that no warnings are emitted if the matrix contains
+        # numbers for which 1/x has no float representation, and that
+        # the solver behaves properly.
+        A = np.array([[1, 2], [3, 4]], dtype=float)
+        A *= 100 * np.nextafter(0, 1)
+
+        b = np.array([1, 1])
+
+        with suppress_warnings() as sup:
+            sup.filter(DeprecationWarning, ".*called without specifying.*")
+            xp, info = gcrotmk(A, b)
+
+        if info == 0:
+            assert_allclose(A.dot(xp), b)

.CondaPkg/env/Lib/site-packages/scipy/sparse/linalg/_isolve/tests/test_iterative.py

@@ -0,0 +1,809 @@
+""" Test functions for the sparse.linalg._isolve module
+"""
+
+import itertools
+import platform
+import sys
+import pytest
+
+import numpy as np
+from numpy.testing import assert_array_equal, assert_allclose
+from numpy import zeros, arange, array, ones, eye, iscomplexobj
+from numpy.linalg import norm
+
+from scipy.sparse import spdiags, csr_matrix, kronsum
+
+from scipy.sparse.linalg import LinearOperator, aslinearoperator
+from scipy.sparse.linalg._isolve import (bicg, bicgstab, cg, cgs,
+                                         gcrotmk, gmres, lgmres,
+                                         minres, qmr, tfqmr)
+
+# TODO check that method preserve shape and type
+# TODO test both preconditioner methods
+
+
+# list of all solvers under test
+_SOLVERS = [bicg, bicgstab, cg, cgs, gcrotmk, gmres, lgmres,
+            minres, qmr, tfqmr]
+
+CB_TYPE_FILTER = ".*called without specifying `callback_type`.*"
+
+
+# create parametrized fixture for easy reuse in tests
+@pytest.fixture(params=_SOLVERS, scope="session")
+def solver(request):
+    """
+    Fixture for all solvers in scipy.sparse.linalg._isolve
+    """
+    return request.param
+
+
+class Case:
+    def __init__(self, name, A, b=None, skip=None, nonconvergence=None):
+        self.name = name
+        self.A = A
+        if b is None:
+            self.b = arange(A.shape[0], dtype=float)
+        else:
+            self.b = b
+        if skip is None:
+            self.skip = []
+        else:
+            self.skip = skip
+        if nonconvergence is None:
+            self.nonconvergence = []
+        else:
+            self.nonconvergence = nonconvergence
+
+
+class SingleTest:
+    def __init__(self, A, b, solver, casename, convergence=True):
+        self.A = A
+        self.b = b
+        self.solver = solver
+        self.name = casename + '-' + solver.__name__
+        self.convergence = convergence
+
+    def __repr__(self):
+        return f"<{self.name}>"
+
+
+class IterativeParams:
+    def __init__(self):
+        sym_solvers = [minres, cg]
+        posdef_solvers = [cg]
+        real_solvers = [minres]
+
+        # list of Cases
+        self.cases = []
+
+        # Symmetric and Positive Definite
+        N = 40
+        data = ones((3, N))
+        data[0, :] = 2
+        data[1, :] = -1
+        data[2, :] = -1
+        Poisson1D = spdiags(data, [0, -1, 1], N, N, format='csr')
+        self.cases.append(Case("poisson1d", Poisson1D))
+        # note: minres fails for single precision
+        self.cases.append(Case("poisson1d-F", Poisson1D.astype('f'),
+                               skip=[minres]))
+
+        # Symmetric and Negative Definite
+        self.cases.append(Case("neg-poisson1d", -Poisson1D,
+                               skip=posdef_solvers))
+        # note: minres fails for single precision
+        self.cases.append(Case("neg-poisson1d-F", (-Poisson1D).astype('f'),
+                               skip=posdef_solvers + [minres]))
+
+        # 2-dimensional Poisson equations
+        Poisson2D = kronsum(Poisson1D, Poisson1D)
+        # note: minres fails for 2-d poisson problem,
+        # it will be fixed in the future PR
+        self.cases.append(Case("poisson2d", Poisson2D, skip=[minres]))
+        # note: minres fails for single precision
+        self.cases.append(Case("poisson2d-F", Poisson2D.astype('f'),
+                               skip=[minres]))
+
+        # Symmetric and Indefinite
+        data = array([[6, -5, 2, 7, -1, 10, 4, -3, -8, 9]], dtype='d')
+        RandDiag = spdiags(data, [0], 10, 10, format='csr')
+        self.cases.append(Case("rand-diag", RandDiag, skip=posdef_solvers))
+        self.cases.append(Case("rand-diag-F", RandDiag.astype('f'),
+                               skip=posdef_solvers))
+
+        # Random real-valued
+        np.random.seed(1234)
+        data = np.random.rand(4, 4)
+        self.cases.append(Case("rand", data,
+                               skip=posdef_solvers + sym_solvers))
+        self.cases.append(Case("rand-F", data.astype('f'),
+                               skip=posdef_solvers + sym_solvers))
+
+        # Random symmetric real-valued
+        np.random.seed(1234)
+        data = np.random.rand(4, 4)
+        data = data + data.T
+        self.cases.append(Case("rand-sym", data, skip=posdef_solvers))
+        self.cases.append(Case("rand-sym-F", data.astype('f'),
+                               skip=posdef_solvers))
+
+        # Random pos-def symmetric real
+        np.random.seed(1234)
+        data = np.random.rand(9, 9)
+        data = np.dot(data.conj(), data.T)
+        self.cases.append(Case("rand-sym-pd", data))
+        # note: minres fails for single precision
+        self.cases.append(Case("rand-sym-pd-F", data.astype('f'),
+                               skip=[minres]))
+
+        # Random complex-valued
+        np.random.seed(1234)
+        data = np.random.rand(4, 4) + 1j * np.random.rand(4, 4)
+        skip_cmplx = posdef_solvers + sym_solvers + real_solvers
+        self.cases.append(Case("rand-cmplx", data, skip=skip_cmplx))
+        self.cases.append(Case("rand-cmplx-F", data.astype('F'),
+                               skip=skip_cmplx))
+
+        # Random hermitian complex-valued
+        np.random.seed(1234)
+        data = np.random.rand(4, 4) + 1j * np.random.rand(4, 4)
+        data = data + data.T.conj()
+        self.cases.append(Case("rand-cmplx-herm", data,
+                               skip=posdef_solvers + real_solvers))
+        self.cases.append(Case("rand-cmplx-herm-F", data.astype('F'),
+                               skip=posdef_solvers + real_solvers))
+
+        # Random pos-def hermitian complex-valued
+        np.random.seed(1234)
+        data = np.random.rand(9, 9) + 1j * np.random.rand(9, 9)
+        data = np.dot(data.conj(), data.T)
+        self.cases.append(Case("rand-cmplx-sym-pd", data, skip=real_solvers))
+        self.cases.append(Case("rand-cmplx-sym-pd-F", data.astype('F'),
+                               skip=real_solvers))
+
+        # Non-symmetric and Positive Definite
+        #
+        # cgs, qmr, bicg and tfqmr fail to converge on this one
+        #   -- algorithmic limitation apparently
+        data = ones((2, 10))
+        data[0, :] = 2
+        data[1, :] = -1
+        A = spdiags(data, [0, -1], 10, 10, format='csr')
+        self.cases.append(Case("nonsymposdef", A,
+                               skip=sym_solvers + [cgs, qmr, bicg, tfqmr]))
+        self.cases.append(Case("nonsymposdef-F", A.astype('F'),
+                               skip=sym_solvers + [cgs, qmr, bicg, tfqmr]))
+
+        # Symmetric, non-pd, hitting cgs/bicg/bicgstab/qmr/tfqmr breakdown
+        A = np.array([[0, 0, 0, 0, 0, 1, -1, -0, -0, -0, -0],
+                      [0, 0, 0, 0, 0, 2, -0, -1, -0, -0, -0],
+                      [0, 0, 0, 0, 0, 2, -0, -0, -1, -0, -0],
+                      [0, 0, 0, 0, 0, 2, -0, -0, -0, -1, -0],
+                      [0, 0, 0, 0, 0, 1, -0, -0, -0, -0, -1],
+                      [1, 2, 2, 2, 1, 0, -0, -0, -0, -0, -0],
+                      [-1, 0, 0, 0, 0, 0, -1, -0, -0, -0, -0],
+                      [0, -1, 0, 0, 0, 0, -0, -1, -0, -0, -0],
+                      [0, 0, -1, 0, 0, 0, -0, -0, -1, -0, -0],
+                      [0, 0, 0, -1, 0, 0, -0, -0, -0, -1, -0],
+                      [0, 0, 0, 0, -1, 0, -0, -0, -0, -0, -1]], dtype=float)
+        b = np.array([0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0], dtype=float)
+        assert (A == A.T).all()
+        self.cases.append(Case("sym-nonpd", A, b,
+                               skip=posdef_solvers,
+                               nonconvergence=[cgs, bicg, bicgstab, qmr, tfqmr]
+                               )
+                          )
+
+    def generate_tests(self):
+        # generate test cases with skips applied
+        tests = []
+        for case in self.cases:
+            for solver in _SOLVERS:
+                if (solver in case.skip):
+                    continue
+                if solver in case.nonconvergence:
+                    tests += [SingleTest(case.A, case.b, solver, case.name,
+                                         convergence=False)]
+                else:
+                    tests += [SingleTest(case.A, case.b, solver, case.name)]
+        return tests
+
+
+cases = IterativeParams().generate_tests()
+
+
+@pytest.fixture(params=cases, ids=[x.name for x in cases], scope="module")
+def case(request):
+    """
+    Fixture for all cases in IterativeParams
+    """
+    return request.param
+
+
+def test_maxiter(case):
+    if not case.convergence:
+        pytest.skip("Solver - Breakdown case, see gh-8829")
+    A = case.A
+    rtol = 1e-12
+
+    b = case.b
+    x0 = 0 * b
+
+    residuals = []
+
+    def callback(x):
+        residuals.append(norm(b - case.A * x))
+
+    if case.solver == gmres:
+        with pytest.warns(DeprecationWarning, match=CB_TYPE_FILTER):
+            x, info = case.solver(A, b, x0=x0, rtol=rtol, maxiter=1, callback=callback)
+    else:
+        x, info = case.solver(A, b, x0=x0, rtol=rtol, maxiter=1, callback=callback)
+
+    assert len(residuals) == 1
+    assert info == 1
+
+
+def test_convergence(case):
+    A = case.A
+
+    if A.dtype.char in "dD":
+        rtol = 1e-8
+    else:
+        rtol = 1e-2
+
+    b = case.b
+    x0 = 0 * b
+
+    x, info = case.solver(A, b, x0=x0, rtol=rtol)
+
+    assert_array_equal(x0, 0 * b)  # ensure that x0 is not overwritten
+    if case.convergence:
+        assert info == 0
+        assert norm(A @ x - b) <= norm(b) * rtol
+    else:
+        assert info != 0
+        assert norm(A @ x - b) <= norm(b)
+
+
+def test_precond_dummy(case):
+    if not case.convergence:
+        pytest.skip("Solver - Breakdown case, see gh-8829")
+
+    rtol = 1e-8
+
+    def identity(b, which=None):
+        """trivial preconditioner"""
+        return b
+
+    A = case.A
+
+    M, N = A.shape
+    # Ensure the diagonal elements of A are non-zero before calculating
+    # 1.0/A.diagonal()
+    diagOfA = A.diagonal()
+    if np.count_nonzero(diagOfA) == len(diagOfA):
+        spdiags([1.0 / diagOfA], [0], M, N)
+
+    b = case.b
+    x0 = 0 * b
+
+    precond = LinearOperator(A.shape, identity, rmatvec=identity)
+
+    if case.solver is qmr:
+        x, info = case.solver(A, b, M1=precond, M2=precond, x0=x0, rtol=rtol)
+    else:
+        x, info = case.solver(A, b, M=precond, x0=x0, rtol=rtol)
+    assert info == 0
+    assert norm(A @ x - b) <= norm(b) * rtol
+
+    A = aslinearoperator(A)
+    A.psolve = identity
+    A.rpsolve = identity
+
+    x, info = case.solver(A, b, x0=x0, rtol=rtol)
+    assert info == 0
+    assert norm(A @ x - b) <= norm(b) * rtol
+
+
+# Specific test for poisson1d and poisson2d cases
+@pytest.mark.fail_slow(5)
+@pytest.mark.parametrize('case', [x for x in IterativeParams().cases
+                                  if x.name in ('poisson1d', 'poisson2d')],
+                         ids=['poisson1d', 'poisson2d'])
+def test_precond_inverse(case):
+    for solver in _SOLVERS:
+        if solver in case.skip or solver is qmr:
+            continue
+
+        rtol = 1e-8
+
+        def inverse(b, which=None):
+            """inverse preconditioner"""
+            A = case.A
+            if not isinstance(A, np.ndarray):
+                A = A.toarray()
+            return np.linalg.solve(A, b)
+
+        def rinverse(b, which=None):
+            """inverse preconditioner"""
+            A = case.A
+            if not isinstance(A, np.ndarray):
+                A = A.toarray()
+            return np.linalg.solve(A.T, b)
+
+        matvec_count = [0]
+
+        def matvec(b):
+            matvec_count[0] += 1
+            return case.A @ b
+
+        def rmatvec(b):
+            matvec_count[0] += 1
+            return case.A.T @ b
+
+        b = case.b
+        x0 = 0 * b
+
+        A = LinearOperator(case.A.shape, matvec, rmatvec=rmatvec)
+        precond = LinearOperator(case.A.shape, inverse, rmatvec=rinverse)
+
+        # Solve with preconditioner
+        matvec_count = [0]
+        x, info = solver(A, b, M=precond, x0=x0, rtol=rtol)
+
+        assert info == 0
+        assert norm(case.A @ x - b) <= norm(b) * rtol
+
+        # Solution should be nearly instant
+        assert matvec_count[0] <= 3
+
+
+def test_atol(solver):
+    # TODO: minres / tfqmr. It didn't historically use absolute tolerances, so
+    # fixing it is less urgent.
+    if solver in (minres, tfqmr):
+        pytest.skip("TODO: Add atol to minres/tfqmr")
+
+    # Historically this is tested as below, all pass but for some reason
+    # gcrotmk is over-sensitive to difference between random.seed/rng.random
+    # Hence tol lower bound is changed from -10 to -9
+    # np.random.seed(1234)
+    # A = np.random.rand(10, 10)
+    # A = A @ A.T + 10 * np.eye(10)
+    # b = 1e3*np.random.rand(10)
+
+    rng = np.random.default_rng(168441431005389)
+    A = rng.uniform(size=[10, 10])
+    A = A @ A.T + 10*np.eye(10)
+    b = 1e3 * rng.uniform(size=10)
+
+    b_norm = np.linalg.norm(b)
+
+    tols = np.r_[0, np.logspace(-9, 2, 7), np.inf]
+
+    # Check effect of badly scaled preconditioners
+    M0 = rng.standard_normal(size=(10, 10))
+    M0 = M0 @ M0.T
+    Ms = [None, 1e-6 * M0, 1e6 * M0]
+
+    for M, rtol, atol in itertools.product(Ms, tols, tols):
+        if rtol == 0 and atol == 0:
+            continue
+
+        if solver is qmr:
+            if M is not None:
+                M = aslinearoperator(M)
+                M2 = aslinearoperator(np.eye(10))
+            else:
+                M2 = None
+            x, info = solver(A, b, M1=M, M2=M2, rtol=rtol, atol=atol)
+        else:
+            x, info = solver(A, b, M=M, rtol=rtol, atol=atol)
+
+        assert info == 0
+        residual = A @ x - b
+        err = np.linalg.norm(residual)
+        atol2 = rtol * b_norm
+        # Added 1.00025 fudge factor because of `err` exceeding `atol` just
+        # very slightly on s390x (see gh-17839)
+        assert err <= 1.00025 * max(atol, atol2)
+
+
+def test_zero_rhs(solver):
+    rng = np.random.default_rng(1684414984100503)
+    A = rng.random(size=[10, 10])
+    A = A @ A.T + 10 * np.eye(10)
+
+    b = np.zeros(10)
+    tols = np.r_[np.logspace(-10, 2, 7)]
+
+    for tol in tols:
+        x, info = solver(A, b, rtol=tol)
+        assert info == 0
+        assert_allclose(x, 0., atol=1e-15)
+
+        x, info = solver(A, b, rtol=tol, x0=ones(10))
+        assert info == 0
+        assert_allclose(x, 0., atol=tol)
+
+        if solver is not minres:
+            x, info = solver(A, b, rtol=tol, atol=0, x0=ones(10))
+            if info == 0:
+                assert_allclose(x, 0)
+
+            x, info = solver(A, b, rtol=tol, atol=tol)
+            assert info == 0
+            assert_allclose(x, 0, atol=1e-300)
+
+            x, info = solver(A, b, rtol=tol, atol=0)
+            assert info == 0
+            assert_allclose(x, 0, atol=1e-300)
+
+
+@pytest.mark.xfail(reason="see gh-18697")
+def test_maxiter_worsening(solver):
+    if solver not in (gmres, lgmres, qmr):
+        # these were skipped from the very beginning, see gh-9201; gh-14160
+        pytest.skip("Solver breakdown case")
+    # Check error does not grow (boundlessly) with increasing maxiter.
+    # This can occur due to the solvers hitting close to breakdown,
+    # which they should detect and halt as necessary.
+    # cf. gh-9100
+    if (solver is gmres and platform.machine() == 'aarch64'
+            and sys.version_info[1] == 9):
+        pytest.xfail(reason="gh-13019")
+    if (solver is lgmres and
+            platform.machine() not in ['x86_64' 'x86', 'aarch64', 'arm64']):
+        # see gh-17839
+        pytest.xfail(reason="fails on at least ppc64le, ppc64 and riscv64")
+
+    # Singular matrix, rhs numerically not in range
+    A = np.array([[-0.1112795288033378, 0, 0, 0.16127952880333685],
+                  [0, -0.13627952880333782 + 6.283185307179586j, 0, 0],
+                  [0, 0, -0.13627952880333782 - 6.283185307179586j, 0],
+                  [0.1112795288033368, 0j, 0j, -0.16127952880333785]])
+    v = np.ones(4)
+    best_error = np.inf
+
+    # Unable to match the Fortran code tolerance levels with this example
+    # Original tolerance values
+
+    # slack_tol = 7 if platform.machine() == 'aarch64' else 5
+    slack_tol = 9
+
+    for maxiter in range(1, 20):
+        x, info = solver(A, v, maxiter=maxiter, rtol=1e-8, atol=0)
+
+        if info == 0:
+            assert norm(A @ x - v) <= 1e-8 * norm(v)
+
+        error = np.linalg.norm(A @ x - v)
+        best_error = min(best_error, error)
+
+        # Check with slack
+        assert error <= slack_tol * best_error
+
+
+def test_x0_working(solver):
+    # Easy problem
+    rng = np.random.default_rng(1685363802304750)
+    n = 10
+    A = rng.random(size=[n, n])
+    A = A @ A.T
+    b = rng.random(n)
+    x0 = rng.random(n)
+
+    if solver is minres:
+        kw = dict(rtol=1e-6)
+    else:
+        kw = dict(atol=0, rtol=1e-6)
+
+    x, info = solver(A, b, **kw)
+    assert info == 0
+    assert norm(A @ x - b) <= 1e-6 * norm(b)
+
+    x, info = solver(A, b, x0=x0, **kw)
+    assert info == 0
+    assert norm(A @ x - b) <= 3e-6*norm(b)
+
+
+def test_x0_equals_Mb(case):
+    if (case.solver is bicgstab) and (case.name == 'nonsymposdef-bicgstab'):
+        pytest.skip("Solver fails due to numerical noise "
+                    "on some architectures (see gh-15533).")
+    if case.solver is tfqmr:
+        pytest.skip("Solver does not support x0='Mb'")
+
+    A = case.A
+    b = case.b
+    x0 = 'Mb'
+    rtol = 1e-8
+    x, info = case.solver(A, b, x0=x0, rtol=rtol)
+
+    assert_array_equal(x0, 'Mb')  # ensure that x0 is not overwritten
+    assert info == 0
+    assert norm(A @ x - b) <= rtol * norm(b)
+
+
+@pytest.mark.parametrize('solver', _SOLVERS)
+def test_x0_solves_problem_exactly(solver):
+    # See gh-19948
+    mat = np.eye(2)
+    rhs = np.array([-1., -1.])
+
+    sol, info = solver(mat, rhs, x0=rhs)
+    assert_allclose(sol, rhs)
+    assert info == 0
+
+
+# Specific tfqmr test
+@pytest.mark.parametrize('case', IterativeParams().cases)
+def test_show(case, capsys):
+    def cb(x):
+        pass
+
+    x, info = tfqmr(case.A, case.b, callback=cb, show=True)
+    out, err = capsys.readouterr()
+
+    if case.name == "sym-nonpd":
+        # no logs for some reason
+        exp = ""
+    elif case.name in ("nonsymposdef", "nonsymposdef-F"):
+        # Asymmetric and Positive Definite
+        exp = "TFQMR: Linear solve not converged due to reach MAXIT iterations"
+    else:  # all other cases
+        exp = "TFQMR: Linear solve converged due to reach TOL iterations"
+
+    assert out.startswith(exp)
+    assert err == ""
+
+
+def test_positional_error(solver):
+    # from test_x0_working
+    rng = np.random.default_rng(1685363802304750)
+    n = 10
+    A = rng.random(size=[n, n])
+    A = A @ A.T
+    b = rng.random(n)
+    x0 = rng.random(n)
+    with pytest.raises(TypeError):
+        solver(A, b, x0, 1e-5)
+
+
+@pytest.mark.parametrize("atol", ["legacy", None, -1])
+def test_invalid_atol(solver, atol):
+    if solver == minres:
+        pytest.skip("minres has no `atol` argument")
+    # from test_x0_working
+    rng = np.random.default_rng(1685363802304750)
+    n = 10
+    A = rng.random(size=[n, n])
+    A = A @ A.T
+    b = rng.random(n)
+    x0 = rng.random(n)
+    with pytest.raises(ValueError):
+        solver(A, b, x0, atol=atol)
+
+
+class TestQMR:
+    @pytest.mark.filterwarnings('ignore::scipy.sparse.SparseEfficiencyWarning')
+    def test_leftright_precond(self):
+        """Check that QMR works with left and right preconditioners"""
+
+        from scipy.sparse.linalg._dsolve import splu
+        from scipy.sparse.linalg._interface import LinearOperator
+
+        n = 100
+
+        dat = ones(n)
+        A = spdiags([-2 * dat, 4 * dat, -dat], [-1, 0, 1], n, n)
+        b = arange(n, dtype='d')
+
+        L = spdiags([-dat / 2, dat], [-1, 0], n, n)
+        U = spdiags([4 * dat, -dat], [0, 1], n, n)
+        L_solver = splu(L)
+        U_solver = splu(U)
+
+        def L_solve(b):
+            return L_solver.solve(b)
+
+        def U_solve(b):
+            return U_solver.solve(b)
+
+        def LT_solve(b):
+            return L_solver.solve(b, 'T')
+
+        def UT_solve(b):
+            return U_solver.solve(b, 'T')
+
+        M1 = LinearOperator((n, n), matvec=L_solve, rmatvec=LT_solve)
+        M2 = LinearOperator((n, n), matvec=U_solve, rmatvec=UT_solve)
+
+        rtol = 1e-8
+        x, info = qmr(A, b, rtol=rtol, maxiter=15, M1=M1, M2=M2)
+
+        assert info == 0
+        assert norm(A @ x - b) <= rtol * norm(b)
+
+
+class TestGMRES:
+    def test_basic(self):
+        A = np.vander(np.arange(10) + 1)[:, ::-1]
+        b = np.zeros(10)
+        b[0] = 1
+
+        x_gm, err = gmres(A, b, restart=5, maxiter=1)
+
+        assert_allclose(x_gm[0], 0.359, rtol=1e-2)
+
+    @pytest.mark.filterwarnings(f"ignore:{CB_TYPE_FILTER}:DeprecationWarning")
+    def test_callback(self):
+
+        def store_residual(r, rvec):
+            rvec[rvec.nonzero()[0].max() + 1] = r
+
+        # Define, A,b
+        A = csr_matrix(array([[-2, 1, 0, 0, 0, 0],
+                              [1, -2, 1, 0, 0, 0],
+                              [0, 1, -2, 1, 0, 0],
+                              [0, 0, 1, -2, 1, 0],
+                              [0, 0, 0, 1, -2, 1],
+                              [0, 0, 0, 0, 1, -2]]))
+        b = ones((A.shape[0],))
+        maxiter = 1
+        rvec = zeros(maxiter + 1)
+        rvec[0] = 1.0
+
+        def callback(r):
+            return store_residual(r, rvec)
+
+        x, flag = gmres(A, b, x0=zeros(A.shape[0]), rtol=1e-16,
+                        maxiter=maxiter, callback=callback)
+
+        # Expected output from SciPy 1.0.0
+        assert_allclose(rvec, array([1.0, 0.81649658092772603]), rtol=1e-10)
+
+        # Test preconditioned callback
+        M = 1e-3 * np.eye(A.shape[0])
+        rvec = zeros(maxiter + 1)
+        rvec[0] = 1.0
+        x, flag = gmres(A, b, M=M, rtol=1e-16, maxiter=maxiter,
+                        callback=callback)
+
+        # Expected output from SciPy 1.0.0
+        # (callback has preconditioned residual!)
+        assert_allclose(rvec, array([1.0, 1e-3 * 0.81649658092772603]),
+                        rtol=1e-10)
+
+    def test_abi(self):
+        # Check we don't segfault on gmres with complex argument
+        A = eye(2)
+        b = ones(2)
+        r_x, r_info = gmres(A, b)
+        r_x = r_x.astype(complex)
+        x, info = gmres(A.astype(complex), b.astype(complex))
+
+        assert iscomplexobj(x)
+        assert_allclose(r_x, x)
+        assert r_info == info
+
+    @pytest.mark.fail_slow(5)
+    def test_atol_legacy(self):
+
+        A = eye(2)
+        b = ones(2)
+        x, info = gmres(A, b, rtol=1e-5)
+        assert np.linalg.norm(A @ x - b) <= 1e-5 * np.linalg.norm(b)
+        assert_allclose(x, b, atol=0, rtol=1e-8)
+
+        rndm = np.random.RandomState(12345)
+        A = rndm.rand(30, 30)
+        b = 1e-6 * ones(30)
+        x, info = gmres(A, b, rtol=1e-7, restart=20)
+        assert np.linalg.norm(A @ x - b) > 1e-7
+
+        A = eye(2)
+        b = 1e-10 * ones(2)
+        x, info = gmres(A, b, rtol=1e-8, atol=0)
+        assert np.linalg.norm(A @ x - b) <= 1e-8 * np.linalg.norm(b)
+
+    def test_defective_precond_breakdown(self):
+        # Breakdown due to defective preconditioner
+        M = np.eye(3)
+        M[2, 2] = 0
+
+        b = np.array([0, 1, 1])
+        x = np.array([1, 0, 0])
+        A = np.diag([2, 3, 4])
+
+        x, info = gmres(A, b, x0=x, M=M, rtol=1e-15, atol=0)
+
+        # Should not return nans, nor terminate with false success
+        assert not np.isnan(x).any()
+        if info == 0:
+            assert np.linalg.norm(A @ x - b) <= 1e-15 * np.linalg.norm(b)
+
+        # The solution should be OK outside null space of M
+        assert_allclose(M @ (A @ x), M @ b)
+
+    def test_defective_matrix_breakdown(self):
+        # Breakdown due to defective matrix
+        A = np.array([[0, 1, 0], [1, 0, 0], [0, 0, 0]])
+        b = np.array([1, 0, 1])
+        rtol = 1e-8
+        x, info = gmres(A, b, rtol=rtol, atol=0)
+
+        # Should not return nans, nor terminate with false success
+        assert not np.isnan(x).any()
+        if info == 0:
+            assert np.linalg.norm(A @ x - b) <= rtol * np.linalg.norm(b)
+
+        # The solution should be OK outside null space of A
+        assert_allclose(A @ (A @ x), A @ b)
+
+    @pytest.mark.filterwarnings(f"ignore:{CB_TYPE_FILTER}:DeprecationWarning")
+    def test_callback_type(self):
+        # The legacy callback type changes meaning of 'maxiter'
+        np.random.seed(1)
+        A = np.random.rand(20, 20)
+        b = np.random.rand(20)
+
+        cb_count = [0]
+
+        def pr_norm_cb(r):
+            cb_count[0] += 1
+            assert isinstance(r, float)
+
+        def x_cb(x):
+            cb_count[0] += 1
+            assert isinstance(x, np.ndarray)
+
+        # 2 iterations is not enough to solve the problem
+        cb_count = [0]
+        x, info = gmres(A, b, rtol=1e-6, atol=0, callback=pr_norm_cb,
+                        maxiter=2, restart=50)
+        assert info == 2
+        assert cb_count[0] == 2
+
+        # With `callback_type` specified, no warning should be raised
+        cb_count = [0]
+        x, info = gmres(A, b, rtol=1e-6, atol=0, callback=pr_norm_cb,
+                        maxiter=2, restart=50, callback_type='legacy')
+        assert info == 2
+        assert cb_count[0] == 2
+
+        # 2 restart cycles is enough to solve the problem
+        cb_count = [0]
+        x, info = gmres(A, b, rtol=1e-6, atol=0, callback=pr_norm_cb,
+                        maxiter=2, restart=50, callback_type='pr_norm')
+        assert info == 0
+        assert cb_count[0] > 2
+
+        # 2 restart cycles is enough to solve the problem
+        cb_count = [0]
+        x, info = gmres(A, b, rtol=1e-6, atol=0, callback=x_cb, maxiter=2,
+                        restart=50, callback_type='x')
+        assert info == 0
+        assert cb_count[0] == 1
+
+    def test_callback_x_monotonic(self):
+        # Check that callback_type='x' gives monotonic norm decrease
+        np.random.seed(1)
+        A = np.random.rand(20, 20) + np.eye(20)
+        b = np.random.rand(20)
+
+        prev_r = [np.inf]
+        count = [0]
+
+        def x_cb(x):
+            r = np.linalg.norm(A @ x - b)
+            assert r <= prev_r[0]
+            prev_r[0] = r
+            count[0] += 1
+
+        x, info = gmres(A, b, rtol=1e-6, atol=0, callback=x_cb, maxiter=20,
+                        restart=10, callback_type='x')
+        assert info == 20
+        assert count[0] == 20

.CondaPkg/env/Lib/site-packages/scipy/sparse/linalg/_isolve/tests/test_lgmres.py

@@ -0,0 +1,211 @@
+"""Tests for the linalg._isolve.lgmres module
+"""
+
+from numpy.testing import (assert_, assert_allclose, assert_equal,
+                           suppress_warnings)
+
+import pytest
+from platform import python_implementation
+
+import numpy as np
+from numpy import zeros, array, allclose
+from scipy.linalg import norm
+from scipy.sparse import csr_matrix, eye, rand
+
+from scipy.sparse.linalg._interface import LinearOperator
+from scipy.sparse.linalg import splu
+from scipy.sparse.linalg._isolve import lgmres, gmres
+
+
+Am = csr_matrix(array([[-2, 1, 0, 0, 0, 9],
+                       [1, -2, 1, 0, 5, 0],
+                       [0, 1, -2, 1, 0, 0],
+                       [0, 0, 1, -2, 1, 0],
+                       [0, 3, 0, 1, -2, 1],
+                       [1, 0, 0, 0, 1, -2]]))
+b = array([1, 2, 3, 4, 5, 6])
+count = [0]
+
+
+def matvec(v):
+    count[0] += 1
+    return Am@v
+
+
+A = LinearOperator(matvec=matvec, shape=Am.shape, dtype=Am.dtype)
+
+
+def do_solve(**kw):
+    count[0] = 0
+    with suppress_warnings() as sup:
+        sup.filter(DeprecationWarning, ".*called without specifying.*")
+        x0, flag = lgmres(A, b, x0=zeros(A.shape[0]),
+                          inner_m=6, rtol=1e-14, **kw)
+    count_0 = count[0]
+    assert_(allclose(A@x0, b, rtol=1e-12, atol=1e-12), norm(A@x0-b))
+    return x0, count_0
+
+
+class TestLGMRES:
+    def test_preconditioner(self):
+        # Check that preconditioning works
+        pc = splu(Am.tocsc())
+        M = LinearOperator(matvec=pc.solve, shape=A.shape, dtype=A.dtype)
+
+        x0, count_0 = do_solve()
+        x1, count_1 = do_solve(M=M)
+
+        assert_(count_1 == 3)
+        assert_(count_1 < count_0/2)
+        assert_(allclose(x1, x0, rtol=1e-14))
+
+    def test_outer_v(self):
+        # Check that the augmentation vectors behave as expected
+
+        outer_v = []
+        x0, count_0 = do_solve(outer_k=6, outer_v=outer_v)
+        assert_(len(outer_v) > 0)
+        assert_(len(outer_v) <= 6)
+
+        x1, count_1 = do_solve(outer_k=6, outer_v=outer_v,
+                               prepend_outer_v=True)
+        assert_(count_1 == 2, count_1)
+        assert_(count_1 < count_0/2)
+        assert_(allclose(x1, x0, rtol=1e-14))
+
+        # ---
+
+        outer_v = []
+        x0, count_0 = do_solve(outer_k=6, outer_v=outer_v,
+                               store_outer_Av=False)
+        assert_(array([v[1] is None for v in outer_v]).all())
+        assert_(len(outer_v) > 0)
+        assert_(len(outer_v) <= 6)
+
+        x1, count_1 = do_solve(outer_k=6, outer_v=outer_v,
+                               prepend_outer_v=True)
+        assert_(count_1 == 3, count_1)
+        assert_(count_1 < count_0/2)
+        assert_(allclose(x1, x0, rtol=1e-14))
+
+    @pytest.mark.skipif(python_implementation() == 'PyPy',
+                        reason="Fails on PyPy CI runs. See #9507")
+    def test_arnoldi(self):
+        np.random.seed(1234)
+
+        A = eye(2000) + rand(2000, 2000, density=5e-4)
+        b = np.random.rand(2000)
+
+        # The inner arnoldi should be equivalent to gmres
+        with suppress_warnings() as sup:
+            sup.filter(DeprecationWarning, ".*called without specifying.*")
+            x0, flag0 = lgmres(A, b, x0=zeros(A.shape[0]),
+                               inner_m=15, maxiter=1)
+            x1, flag1 = gmres(A, b, x0=zeros(A.shape[0]),
+                              restart=15, maxiter=1)
+
+        assert_equal(flag0, 1)
+        assert_equal(flag1, 1)
+        norm = np.linalg.norm(A.dot(x0) - b)
+        assert_(norm > 1e-4)
+        assert_allclose(x0, x1)
+
+    def test_cornercase(self):
+        np.random.seed(1234)
+
+        # Rounding error may prevent convergence with tol=0 --- ensure
+        # that the return values in this case are correct, and no
+        # exceptions are raised
+
+        for n in [3, 5, 10, 100]:
+            A = 2*eye(n)
+
+            with suppress_warnings() as sup:
+                sup.filter(DeprecationWarning, ".*called without specifying.*")
+
+                b = np.ones(n)
+                x, info = lgmres(A, b, maxiter=10)
+                assert_equal(info, 0)
+                assert_allclose(A.dot(x) - b, 0, atol=1e-14)
+
+                x, info = lgmres(A, b, rtol=0, maxiter=10)
+                if info == 0:
+                    assert_allclose(A.dot(x) - b, 0, atol=1e-14)
+
+                b = np.random.rand(n)
+                x, info = lgmres(A, b, maxiter=10)
+                assert_equal(info, 0)
+                assert_allclose(A.dot(x) - b, 0, atol=1e-14)
+
+                x, info = lgmres(A, b, rtol=0, maxiter=10)
+                if info == 0:
+                    assert_allclose(A.dot(x) - b, 0, atol=1e-14)
+
+    def test_nans(self):
+        A = eye(3, format='lil')
+        A[1, 1] = np.nan
+        b = np.ones(3)
+
+        with suppress_warnings() as sup:
+            sup.filter(DeprecationWarning, ".*called without specifying.*")
+            x, info = lgmres(A, b, rtol=0, maxiter=10)
+            assert_equal(info, 1)
+
+    def test_breakdown_with_outer_v(self):
+        A = np.array([[1, 2], [3, 4]], dtype=float)
+        b = np.array([1, 2])
+
+        x = np.linalg.solve(A, b)
+        v0 = np.array([1, 0])
+
+        # The inner iteration should converge to the correct solution,
+        # since it's in the outer vector list
+        with suppress_warnings() as sup:
+            sup.filter(DeprecationWarning, ".*called without specifying.*")
+            xp, info = lgmres(A, b, outer_v=[(v0, None), (x, None)], maxiter=1)
+
+        assert_allclose(xp, x, atol=1e-12)
+
+    def test_breakdown_underdetermined(self):
+        # Should find LSQ solution in the Krylov span in one inner
+        # iteration, despite solver breakdown from nilpotent A.
+        A = np.array([[0, 1, 1, 1],
+                      [0, 0, 1, 1],
+                      [0, 0, 0, 1],
+                      [0, 0, 0, 0]], dtype=float)
+
+        bs = [
+            np.array([1, 1, 1, 1]),
+            np.array([1, 1, 1, 0]),
+            np.array([1, 1, 0, 0]),
+            np.array([1, 0, 0, 0]),
+        ]
+
+        for b in bs:
+            with suppress_warnings() as sup:
+                sup.filter(DeprecationWarning, ".*called without specifying.*")
+                xp, info = lgmres(A, b, maxiter=1)
+            resp = np.linalg.norm(A.dot(xp) - b)
+
+            K = np.c_[b, A.dot(b), A.dot(A.dot(b)), A.dot(A.dot(A.dot(b)))]
+            y, _, _, _ = np.linalg.lstsq(A.dot(K), b, rcond=-1)
+            x = K.dot(y)
+            res = np.linalg.norm(A.dot(x) - b)
+
+            assert_allclose(resp, res, err_msg=repr(b))
+
+    def test_denormals(self):
+        # Check that no warnings are emitted if the matrix contains
+        # numbers for which 1/x has no float representation, and that
+        # the solver behaves properly.
+        A = np.array([[1, 2], [3, 4]], dtype=float)
+        A *= 100 * np.nextafter(0, 1)
+
+        b = np.array([1, 1])
+
+        with suppress_warnings() as sup:
+            sup.filter(DeprecationWarning, ".*called without specifying.*")
+            xp, info = lgmres(A, b)
+
+        if info == 0:
+            assert_allclose(A.dot(xp), b)

.CondaPkg/env/Lib/site-packages/scipy/sparse/linalg/_isolve/tests/test_lsmr.py

@@ -0,0 +1,185 @@
+"""
+Copyright (C) 2010 David Fong and Michael Saunders
+Distributed under the same license as SciPy
+
+Testing Code for LSMR.
+
+03 Jun 2010: First version release with lsmr.py
+
+David Chin-lung Fong            clfong@stanford.edu
+Institute for Computational and Mathematical Engineering
+Stanford University
+
+Michael Saunders                saunders@stanford.edu
+Systems Optimization Laboratory
+Dept of MS&E, Stanford University.
+
+"""
+
+from numpy import array, arange, eye, zeros, ones, transpose, hstack
+from numpy.linalg import norm
+from numpy.testing import assert_allclose
+import pytest
+from scipy.sparse import coo_matrix
+from scipy.sparse.linalg._interface import aslinearoperator
+from scipy.sparse.linalg import lsmr
+from .test_lsqr import G, b
+
+
+class TestLSMR:
+    def setup_method(self):
+        self.n = 10
+        self.m = 10
+
+    def assertCompatibleSystem(self, A, xtrue):
+        Afun = aslinearoperator(A)
+        b = Afun.matvec(xtrue)
+        x = lsmr(A, b)[0]
+        assert norm(x - xtrue) == pytest.approx(0, abs=1e-5)
+
+    def testIdentityACase1(self):
+        A = eye(self.n)
+        xtrue = zeros((self.n, 1))
+        self.assertCompatibleSystem(A, xtrue)
+
+    def testIdentityACase2(self):
+        A = eye(self.n)
+        xtrue = ones((self.n,1))
+        self.assertCompatibleSystem(A, xtrue)
+
+    def testIdentityACase3(self):
+        A = eye(self.n)
+        xtrue = transpose(arange(self.n,0,-1))
+        self.assertCompatibleSystem(A, xtrue)
+
+    def testBidiagonalA(self):
+        A = lowerBidiagonalMatrix(20,self.n)
+        xtrue = transpose(arange(self.n,0,-1))
+        self.assertCompatibleSystem(A,xtrue)
+
+    def testScalarB(self):
+        A = array([[1.0, 2.0]])
+        b = 3.0
+        x = lsmr(A, b)[0]
+        assert norm(A.dot(x) - b) == pytest.approx(0)
+
+    def testComplexX(self):
+        A = eye(self.n)
+        xtrue = transpose(arange(self.n, 0, -1) * (1 + 1j))
+        self.assertCompatibleSystem(A, xtrue)
+
+    def testComplexX0(self):
+        A = 4 * eye(self.n) + ones((self.n, self.n))
+        xtrue = transpose(arange(self.n, 0, -1))
+        b = aslinearoperator(A).matvec(xtrue)
+        x0 = zeros(self.n, dtype=complex)
+        x = lsmr(A, b, x0=x0)[0]
+        assert norm(x - xtrue) == pytest.approx(0, abs=1e-5)
+
+    def testComplexA(self):
+        A = 4 * eye(self.n) + 1j * ones((self.n, self.n))
+        xtrue = transpose(arange(self.n, 0, -1).astype(complex))
+        self.assertCompatibleSystem(A, xtrue)
+
+    def testComplexB(self):
+        A = 4 * eye(self.n) + ones((self.n, self.n))
+        xtrue = transpose(arange(self.n, 0, -1) * (1 + 1j))
+        b = aslinearoperator(A).matvec(xtrue)
+        x = lsmr(A, b)[0]
+        assert norm(x - xtrue) == pytest.approx(0, abs=1e-5)
+
+    def testColumnB(self):
+        A = eye(self.n)
+        b = ones((self.n, 1))
+        x = lsmr(A, b)[0]
+        assert norm(A.dot(x) - b.ravel()) == pytest.approx(0)
+
+    def testInitialization(self):
+        # Test that the default setting is not modified
+        x_ref, _, itn_ref, normr_ref, *_ = lsmr(G, b)
+        assert_allclose(norm(b - G@x_ref), normr_ref, atol=1e-6)
+
+        # Test passing zeros yields similar result
+        x0 = zeros(b.shape)
+        x = lsmr(G, b, x0=x0)[0]
+        assert_allclose(x, x_ref)
+
+        # Test warm-start with single iteration
+        x0 = lsmr(G, b, maxiter=1)[0]
+
+        x, _, itn, normr, *_ = lsmr(G, b, x0=x0)
+        assert_allclose(norm(b - G@x), normr, atol=1e-6)
+
+        # NOTE(gh-12139): This doesn't always converge to the same value as
+        # ref because error estimates will be slightly different when calculated
+        # from zeros vs x0 as a result only compare norm and itn (not x).
+
+        # x generally converges 1 iteration faster because it started at x0.
+        # itn == itn_ref means that lsmr(x0) took an extra iteration see above.
+        # -1 is technically possible but is rare (1 in 100000) so it's more
+        # likely to be an error elsewhere.
+        assert itn - itn_ref in (0, 1)
+
+        # If an extra iteration is performed normr may be 0, while normr_ref
+        # may be much larger.
+        assert normr < normr_ref * (1 + 1e-6)
+
+
+class TestLSMRReturns:
+    def setup_method(self):
+        self.n = 10
+        self.A = lowerBidiagonalMatrix(20, self.n)
+        self.xtrue = transpose(arange(self.n, 0, -1))
+        self.Afun = aslinearoperator(self.A)
+        self.b = self.Afun.matvec(self.xtrue)
+        self.x0 = ones(self.n)
+        self.x00 = self.x0.copy()
+        self.returnValues = lsmr(self.A, self.b)
+        self.returnValuesX0 = lsmr(self.A, self.b, x0=self.x0)
+
+    def test_unchanged_x0(self):
+        x, istop, itn, normr, normar, normA, condA, normx = self.returnValuesX0
+        assert_allclose(self.x00, self.x0)
+
+    def testNormr(self):
+        x, istop, itn, normr, normar, normA, condA, normx = self.returnValues
+        assert norm(self.b - self.Afun.matvec(x)) == pytest.approx(normr)
+
+    def testNormar(self):
+        x, istop, itn, normr, normar, normA, condA, normx = self.returnValues
+        assert (norm(self.Afun.rmatvec(self.b - self.Afun.matvec(x)))
+                == pytest.approx(normar))
+
+    def testNormx(self):
+        x, istop, itn, normr, normar, normA, condA, normx = self.returnValues
+        assert norm(x) == pytest.approx(normx)
+
+
+def lowerBidiagonalMatrix(m, n):
+    # This is a simple example for testing LSMR.
+    # It uses the leading m*n submatrix from
+    # A = [ 1
+    #       1 2
+    #         2 3
+    #           3 4
+    #             ...
+    #               n ]
+    # suitably padded by zeros.
+    #
+    # 04 Jun 2010: First version for distribution with lsmr.py
+    if m <= n:
+        row = hstack((arange(m, dtype=int),
+                      arange(1, m, dtype=int)))
+        col = hstack((arange(m, dtype=int),
+                      arange(m-1, dtype=int)))
+        data = hstack((arange(1, m+1, dtype=float),
+                       arange(1,m, dtype=float)))
+        return coo_matrix((data, (row, col)), shape=(m,n))
+    else:
+        row = hstack((arange(n, dtype=int),
+                      arange(1, n+1, dtype=int)))
+        col = hstack((arange(n, dtype=int),
+                      arange(n, dtype=int)))
+        data = hstack((arange(1, n+1, dtype=float),
+                       arange(1,n+1, dtype=float)))
+        return coo_matrix((data,(row, col)), shape=(m,n))

.CondaPkg/env/Lib/site-packages/scipy/sparse/linalg/_isolve/tests/test_lsqr.py

@@ -0,0 +1,120 @@
+import numpy as np
+from numpy.testing import assert_allclose, assert_array_equal, assert_equal
+import pytest
+import scipy.sparse
+import scipy.sparse.linalg
+from scipy.sparse.linalg import lsqr
+
+# Set up a test problem
+n = 35
+G = np.eye(n)
+normal = np.random.normal
+norm = np.linalg.norm
+
+for jj in range(5):
+    gg = normal(size=n)
+    hh = gg * gg.T
+    G += (hh + hh.T) * 0.5
+    G += normal(size=n) * normal(size=n)
+
+b = normal(size=n)
+
+# tolerance for atol/btol keywords of lsqr()
+tol = 2e-10
+# tolerances for testing the results of the lsqr() call with assert_allclose
+# These tolerances are a bit fragile - see discussion in gh-15301.
+atol_test = 4e-10
+rtol_test = 2e-8
+show = False
+maxit = None
+
+
+def test_lsqr_basic():
+    b_copy = b.copy()
+    xo, *_ = lsqr(G, b, show=show, atol=tol, btol=tol, iter_lim=maxit)
+    assert_array_equal(b_copy, b)
+
+    svx = np.linalg.solve(G, b)
+    assert_allclose(xo, svx, atol=atol_test, rtol=rtol_test)
+
+    # Now the same but with damp > 0.
+    # This is equivalent to solving the extended system:
+    # ( G      ) @ x = ( b )
+    # ( damp*I )       ( 0 )
+    damp = 1.5
+    xo, *_ = lsqr(
+        G, b, damp=damp, show=show, atol=tol, btol=tol, iter_lim=maxit)
+
+    Gext = np.r_[G, damp * np.eye(G.shape[1])]
+    bext = np.r_[b, np.zeros(G.shape[1])]
+    svx, *_ = np.linalg.lstsq(Gext, bext, rcond=None)
+    assert_allclose(xo, svx, atol=atol_test, rtol=rtol_test)
+
+
+def test_gh_2466():
+    row = np.array([0, 0])
+    col = np.array([0, 1])
+    val = np.array([1, -1])
+    A = scipy.sparse.coo_matrix((val, (row, col)), shape=(1, 2))
+    b = np.asarray([4])
+    lsqr(A, b)
+
+
+def test_well_conditioned_problems():
+    # Test that sparse the lsqr solver returns the right solution
+    # on various problems with different random seeds.
+    # This is a non-regression test for a potential ZeroDivisionError
+    # raised when computing the `test2` & `test3` convergence conditions.
+    n = 10
+    A_sparse = scipy.sparse.eye(n, n)
+    A_dense = A_sparse.toarray()
+
+    with np.errstate(invalid='raise'):
+        for seed in range(30):
+            rng = np.random.RandomState(seed + 10)
+            beta = rng.rand(n)
+            beta[beta == 0] = 0.00001  # ensure that all the betas are not null
+            b = A_sparse @ beta[:, np.newaxis]
+            output = lsqr(A_sparse, b, show=show)
+
+            # Check that the termination condition corresponds to an approximate
+            # solution to Ax = b
+            assert_equal(output[1], 1)
+            solution = output[0]
+
+            # Check that we recover the ground truth solution
+            assert_allclose(solution, beta)
+
+            # Sanity check: compare to the dense array solver
+            reference_solution = np.linalg.solve(A_dense, b).ravel()
+            assert_allclose(solution, reference_solution)
+
+
+def test_b_shapes():
+    # Test b being a scalar.
+    A = np.array([[1.0, 2.0]])
+    b = 3.0
+    x = lsqr(A, b)[0]
+    assert norm(A.dot(x) - b) == pytest.approx(0)
+
+    # Test b being a column vector.
+    A = np.eye(10)
+    b = np.ones((10, 1))
+    x = lsqr(A, b)[0]
+    assert norm(A.dot(x) - b.ravel()) == pytest.approx(0)
+
+
+def test_initialization():
+    # Test the default setting is the same as zeros
+    b_copy = b.copy()
+    x_ref = lsqr(G, b, show=show, atol=tol, btol=tol, iter_lim=maxit)
+    x0 = np.zeros(x_ref[0].shape)
+    x = lsqr(G, b, show=show, atol=tol, btol=tol, iter_lim=maxit, x0=x0)
+    assert_array_equal(b_copy, b)
+    assert_allclose(x_ref[0], x[0])
+
+    # Test warm-start with single iteration
+    x0 = lsqr(G, b, show=show, atol=tol, btol=tol, iter_lim=1)[0]
+    x = lsqr(G, b, show=show, atol=tol, btol=tol, iter_lim=maxit, x0=x0)
+    assert_allclose(x_ref[0], x[0])
+    assert_array_equal(b_copy, b)

.CondaPkg/env/Lib/site-packages/scipy/sparse/linalg/_isolve/tests/test_minres.py

@@ -0,0 +1,97 @@
+import numpy as np
+from numpy.linalg import norm
+from numpy.testing import assert_equal, assert_allclose, assert_
+from scipy.sparse.linalg._isolve import minres
+
+from pytest import raises as assert_raises
+
+
+def get_sample_problem():
+    # A random 10 x 10 symmetric matrix
+    np.random.seed(1234)
+    matrix = np.random.rand(10, 10)
+    matrix = matrix + matrix.T
+    # A random vector of length 10
+    vector = np.random.rand(10)
+    return matrix, vector
+
+
+def test_singular():
+    A, b = get_sample_problem()
+    A[0, ] = 0
+    b[0] = 0
+    xp, info = minres(A, b)
+    assert_equal(info, 0)
+    assert norm(A @ xp - b) <= 1e-5 * norm(b)
+
+
+def test_x0_is_used_by():
+    A, b = get_sample_problem()
+    # Random x0 to feed minres
+    np.random.seed(12345)
+    x0 = np.random.rand(10)
+    trace = []
+
+    def trace_iterates(xk):
+        trace.append(xk)
+    minres(A, b, x0=x0, callback=trace_iterates)
+    trace_with_x0 = trace
+
+    trace = []
+    minres(A, b, callback=trace_iterates)
+    assert_(not np.array_equal(trace_with_x0[0], trace[0]))
+
+
+def test_shift():
+    A, b = get_sample_problem()
+    shift = 0.5
+    shifted_A = A - shift * np.eye(10)
+    x1, info1 = minres(A, b, shift=shift)
+    x2, info2 = minres(shifted_A, b)
+    assert_equal(info1, 0)
+    assert_allclose(x1, x2, rtol=1e-5)
+
+
+def test_asymmetric_fail():
+    """Asymmetric matrix should raise `ValueError` when check=True"""
+    A, b = get_sample_problem()
+    A[1, 2] = 1
+    A[2, 1] = 2
+    with assert_raises(ValueError):
+        xp, info = minres(A, b, check=True)
+
+
+def test_minres_non_default_x0():
+    np.random.seed(1234)
+    rtol = 1e-6
+    a = np.random.randn(5, 5)
+    a = np.dot(a, a.T)
+    b = np.random.randn(5)
+    c = np.random.randn(5)
+    x = minres(a, b, x0=c, rtol=rtol)[0]
+    assert norm(a @ x - b) <= rtol * norm(b)
+
+
+def test_minres_precond_non_default_x0():
+    np.random.seed(12345)
+    rtol = 1e-6
+    a = np.random.randn(5, 5)
+    a = np.dot(a, a.T)
+    b = np.random.randn(5)
+    c = np.random.randn(5)
+    m = np.random.randn(5, 5)
+    m = np.dot(m, m.T)
+    x = minres(a, b, M=m, x0=c, rtol=rtol)[0]
+    assert norm(a @ x - b) <= rtol * norm(b)
+
+
+def test_minres_precond_exact_x0():
+    np.random.seed(1234)
+    rtol = 1e-6
+    a = np.eye(10)
+    b = np.ones(10)
+    c = np.ones(10)
+    m = np.random.randn(10, 10)
+    m = np.dot(m, m.T)
+    x = minres(a, b, M=m, x0=c, rtol=rtol)[0]
+    assert norm(a @ x - b) <= rtol * norm(b)

.CondaPkg/env/Lib/site-packages/scipy/sparse/linalg/_isolve/tests/test_utils.py

@@ -0,0 +1,9 @@
+import numpy as np
+from pytest import raises as assert_raises
+
+import scipy.sparse.linalg._isolve.utils as utils
+
+
+def test_make_system_bad_shape():
+    assert_raises(ValueError,
+                  utils.make_system, np.zeros((5,3)), None, np.zeros(4), np.zeros(4))

.CondaPkg/env/Lib/site-packages/scipy/sparse/linalg/_isolve/tfqmr.py

@@ -0,0 +1,179 @@
+import numpy as np
+from .iterative import _get_atol_rtol
+from .utils import make_system
+
+
+__all__ = ['tfqmr']
+
+
+def tfqmr(A, b, x0=None, *, rtol=1e-5, atol=0., maxiter=None, M=None,
+          callback=None, show=False):
+    """
+    Use Transpose-Free Quasi-Minimal Residual iteration to solve ``Ax = b``.
+
+    Parameters
+    ----------
+    A : {sparse matrix, ndarray, LinearOperator}
+        The real or complex N-by-N matrix of the linear system.
+        Alternatively, `A` can be a linear operator which can
+        produce ``Ax`` using, e.g.,
+        `scipy.sparse.linalg.LinearOperator`.
+    b : {ndarray}
+        Right hand side of the linear system. Has shape (N,) or (N,1).
+    x0 : {ndarray}
+        Starting guess for the solution.
+    rtol, atol : float, optional
+        Parameters for the convergence test. For convergence,
+        ``norm(b - A @ x) <= max(rtol*norm(b), atol)`` should be satisfied.
+        The default is ``rtol=1e-5``, the default for ``atol`` is ``0.0``.
+    maxiter : int, optional
+        Maximum number of iterations.  Iteration will stop after maxiter
+        steps even if the specified tolerance has not been achieved.
+        Default is ``min(10000, ndofs * 10)``, where ``ndofs = A.shape[0]``.
+    M : {sparse matrix, ndarray, LinearOperator}
+        Inverse of the preconditioner of A.  M should approximate the
+        inverse of A and be easy to solve for (see Notes).  Effective
+        preconditioning dramatically improves the rate of convergence,
+        which implies that fewer iterations are needed to reach a given
+        error tolerance.  By default, no preconditioner is used.
+    callback : function, optional
+        User-supplied function to call after each iteration.  It is called
+        as `callback(xk)`, where `xk` is the current solution vector.
+    show : bool, optional
+        Specify ``show = True`` to show the convergence, ``show = False`` is
+        to close the output of the convergence.
+        Default is `False`.
+
+    Returns
+    -------
+    x : ndarray
+        The converged solution.
+    info : int
+        Provides convergence information:
+
+            - 0  : successful exit
+            - >0 : convergence to tolerance not achieved, number of iterations
+            - <0 : illegal input or breakdown
+
+    Notes
+    -----
+    The Transpose-Free QMR algorithm is derived from the CGS algorithm.
+    However, unlike CGS, the convergence curves for the TFQMR method is
+    smoothed by computing a quasi minimization of the residual norm. The
+    implementation supports left preconditioner, and the "residual norm"
+    to compute in convergence criterion is actually an upper bound on the
+    actual residual norm ``||b - Axk||``.
+
+    References
+    ----------
+    .. [1] R. W. Freund, A Transpose-Free Quasi-Minimal Residual Algorithm for
+           Non-Hermitian Linear Systems, SIAM J. Sci. Comput., 14(2), 470-482,
+           1993.
+    .. [2] Y. Saad, Iterative Methods for Sparse Linear Systems, 2nd edition,
+           SIAM, Philadelphia, 2003.
+    .. [3] C. T. Kelley, Iterative Methods for Linear and Nonlinear Equations,
+           number 16 in Frontiers in Applied Mathematics, SIAM, Philadelphia,
+           1995.
+
+    Examples
+    --------
+    >>> import numpy as np
+    >>> from scipy.sparse import csc_matrix
+    >>> from scipy.sparse.linalg import tfqmr
+    >>> A = csc_matrix([[3, 2, 0], [1, -1, 0], [0, 5, 1]], dtype=float)
+    >>> b = np.array([2, 4, -1], dtype=float)
+    >>> x, exitCode = tfqmr(A, b, atol=0.0)
+    >>> print(exitCode)            # 0 indicates successful convergence
+    0
+    >>> np.allclose(A.dot(x), b)
+    True
+    """
+
+    # Check data type
+    dtype = A.dtype
+    if np.issubdtype(dtype, np.int64):
+        dtype = float
+        A = A.astype(dtype)
+    if np.issubdtype(b.dtype, np.int64):
+        b = b.astype(dtype)
+
+    A, M, x, b, postprocess = make_system(A, M, x0, b)
+
+    # Check if the R.H.S is a zero vector
+    if np.linalg.norm(b) == 0.:
+        x = b.copy()
+        return (postprocess(x), 0)
+
+    ndofs = A.shape[0]
+    if maxiter is None:
+        maxiter = min(10000, ndofs * 10)
+
+    if x0 is None:
+        r = b.copy()
+    else:
+        r = b - A.matvec(x)
+    u = r
+    w = r.copy()
+    # Take rstar as b - Ax0, that is rstar := r = b - Ax0 mathematically
+    rstar = r
+    v = M.matvec(A.matvec(r))
+    uhat = v
+    d = theta = eta = 0.
+    # at this point we know rstar == r, so rho is always real
+    rho = np.inner(rstar.conjugate(), r).real
+    rhoLast = rho
+    r0norm = np.sqrt(rho)
+    tau = r0norm
+    if r0norm == 0:
+        return (postprocess(x), 0)
+
+    # we call this to get the right atol and raise errors as necessary
+    atol, _ = _get_atol_rtol('tfqmr', r0norm, atol, rtol)
+
+    for iter in range(maxiter):
+        even = iter % 2 == 0
+        if (even):
+            vtrstar = np.inner(rstar.conjugate(), v)
+            # Check breakdown
+            if vtrstar == 0.:
+                return (postprocess(x), -1)
+            alpha = rho / vtrstar
+            uNext = u - alpha * v  # [1]-(5.6)
+        w -= alpha * uhat  # [1]-(5.8)
+        d = u + (theta**2 / alpha) * eta * d  # [1]-(5.5)
+        # [1]-(5.2)
+        theta = np.linalg.norm(w) / tau
+        c = np.sqrt(1. / (1 + theta**2))
+        tau *= theta * c
+        # Calculate step and direction [1]-(5.4)
+        eta = (c**2) * alpha
+        z = M.matvec(d)
+        x += eta * z
+
+        if callback is not None:
+            callback(x)
+
+        # Convergence criterion
+        if tau * np.sqrt(iter+1) < atol:
+            if (show):
+                print("TFQMR: Linear solve converged due to reach TOL "
+                      f"iterations {iter+1}")
+            return (postprocess(x), 0)
+
+        if (not even):
+            # [1]-(5.7)
+            rho = np.inner(rstar.conjugate(), w)
+            beta = rho / rhoLast
+            u = w + beta * u
+            v = beta * uhat + (beta**2) * v
+            uhat = M.matvec(A.matvec(u))
+            v += uhat
+        else:
+            uhat = M.matvec(A.matvec(uNext))
+            u = uNext
+            rhoLast = rho
+
+    if (show):
+        print("TFQMR: Linear solve not converged due to reach MAXIT "
+              f"iterations {iter+1}")
+    return (postprocess(x), maxiter)

.CondaPkg/env/Lib/site-packages/scipy/sparse/linalg/_isolve/utils.py

@@ -0,0 +1,127 @@
+__docformat__ = "restructuredtext en"
+
+__all__ = []
+
+
+from numpy import asanyarray, asarray, array, zeros
+
+from scipy.sparse.linalg._interface import aslinearoperator, LinearOperator, \
+     IdentityOperator
+
+_coerce_rules = {('f','f'):'f', ('f','d'):'d', ('f','F'):'F',
+                 ('f','D'):'D', ('d','f'):'d', ('d','d'):'d',
+                 ('d','F'):'D', ('d','D'):'D', ('F','f'):'F',
+                 ('F','d'):'D', ('F','F'):'F', ('F','D'):'D',
+                 ('D','f'):'D', ('D','d'):'D', ('D','F'):'D',
+                 ('D','D'):'D'}
+
+
+def coerce(x,y):
+    if x not in 'fdFD':
+        x = 'd'
+    if y not in 'fdFD':
+        y = 'd'
+    return _coerce_rules[x,y]
+
+
+def id(x):
+    return x
+
+
+def make_system(A, M, x0, b):
+    """Make a linear system Ax=b
+
+    Parameters
+    ----------
+    A : LinearOperator
+        sparse or dense matrix (or any valid input to aslinearoperator)
+    M : {LinearOperator, Nones}
+        preconditioner
+        sparse or dense matrix (or any valid input to aslinearoperator)
+    x0 : {array_like, str, None}
+        initial guess to iterative method.
+        ``x0 = 'Mb'`` means using the nonzero initial guess ``M @ b``.
+        Default is `None`, which means using the zero initial guess.
+    b : array_like
+        right hand side
+
+    Returns
+    -------
+    (A, M, x, b, postprocess)
+        A : LinearOperator
+            matrix of the linear system
+        M : LinearOperator
+            preconditioner
+        x : rank 1 ndarray
+            initial guess
+        b : rank 1 ndarray
+            right hand side
+        postprocess : function
+            converts the solution vector to the appropriate
+            type and dimensions (e.g. (N,1) matrix)
+
+    """
+    A_ = A
+    A = aslinearoperator(A)
+
+    if A.shape[0] != A.shape[1]:
+        raise ValueError(f'expected square matrix, but got shape={(A.shape,)}')
+
+    N = A.shape[0]
+
+    b = asanyarray(b)
+
+    if not (b.shape == (N,1) or b.shape == (N,)):
+        raise ValueError(f'shapes of A {A.shape} and b {b.shape} are '
+                         'incompatible')
+
+    if b.dtype.char not in 'fdFD':
+        b = b.astype('d')  # upcast non-FP types to double
+
+    def postprocess(x):
+        return x
+
+    if hasattr(A,'dtype'):
+        xtype = A.dtype.char
+    else:
+        xtype = A.matvec(b).dtype.char
+    xtype = coerce(xtype, b.dtype.char)
+
+    b = asarray(b,dtype=xtype)  # make b the same type as x
+    b = b.ravel()
+
+    # process preconditioner
+    if M is None:
+        if hasattr(A_,'psolve'):
+            psolve = A_.psolve
+        else:
+            psolve = id
+        if hasattr(A_,'rpsolve'):
+            rpsolve = A_.rpsolve
+        else:
+            rpsolve = id
+        if psolve is id and rpsolve is id:
+            M = IdentityOperator(shape=A.shape, dtype=A.dtype)
+        else:
+            M = LinearOperator(A.shape, matvec=psolve, rmatvec=rpsolve,
+                               dtype=A.dtype)
+    else:
+        M = aslinearoperator(M)
+        if A.shape != M.shape:
+            raise ValueError('matrix and preconditioner have different shapes')
+
+    # set initial guess
+    if x0 is None:
+        x = zeros(N, dtype=xtype)
+    elif isinstance(x0, str):
+        if x0 == 'Mb':  # use nonzero initial guess ``M @ b``
+            bCopy = b.copy()
+            x = M.matvec(bCopy)
+    else:
+        x = array(x0, dtype=xtype)
+        if not (x.shape == (N, 1) or x.shape == (N,)):
+            raise ValueError(f'shapes of A {A.shape} and '
+                             f'x0 {x.shape} are incompatible')
+        x = x.ravel()
+
+    return A, M, x, b, postprocess