"""
Find a few eigenvectors and eigenvalues of a matrix.
Uses ARPACK: http://www.caam.rice.edu/software/ARPACK/
"""
# Wrapper implementation notes
#
# ARPACK Entry Points
# -------------------
# The entry points to ARPACK are
# - (s,d)seupd : single and double precision symmetric matrix
# - (s,d,c,z)neupd: single,double,complex,double complex general matrix
# This wrapper puts the *neupd (general matrix) interfaces in eigs()
# and the *seupd (symmetric matrix) in eigsh().
# There is no Hermetian complex/double complex interface.
# To find eigenvalues of a Hermetian matrix you
# must use eigs() and not eigsh()
# It might be desirable to handle the Hermetian case differently
# and, for example, return real eigenvalues.
# Number of eigenvalues returned and complex eigenvalues
# ------------------------------------------------------
# The ARPACK nonsymmetric real and double interface (s,d)naupd return
# eigenvalues and eigenvectors in real (float,double) arrays.
# Since the eigenvalues and eigenvectors are, in general, complex
# ARPACK puts the real and imaginary parts in consecutive entries
# in real-valued arrays. This wrapper puts the real entries
# into complex data types and attempts to return the requested eigenvalues
# and eigenvectors.
# Solver modes
# ------------
# ARPACK and handle shifted and shift-inverse computations
# for eigenvalues by providing a shift (sigma) and a solver.
from __future__ import division, print_function, absolute_import
__docformat__ = "restructuredtext en"
__all__ = ['eigs', 'eigsh', 'svds', 'ArpackError', 'ArpackNoConvergence']
from . import _arpack
import numpy as np
from scipy.sparse.linalg.interface import aslinearoperator, LinearOperator
from scipy.sparse import eye, isspmatrix, isspmatrix_csr
from scipy.linalg import lu_factor, lu_solve
from scipy.sparse.sputils import isdense
from scipy.sparse.linalg import gmres, splu
from scipy._lib._util import _aligned_zeros
_type_conv = {'f': 's', 'd': 'd', 'F': 'c', 'D': 'z'}
_ndigits = {'f': 5, 'd': 12, 'F': 5, 'D': 12}
DNAUPD_ERRORS = {
0: "Normal exit.",
1: "Maximum number of iterations taken. "
"All possible eigenvalues of OP has been found. IPARAM(5) "
"returns the number of wanted converged Ritz values.",
2: "No longer an informational error. Deprecated starting "
"with release 2 of ARPACK.",
3: "No shifts could be applied during a cycle of the "
"Implicitly restarted Arnoldi iteration. One possibility "
"is to increase the size of NCV relative to NEV. ",
-1: "N must be positive.",
-2: "NEV must be positive.",
-3: "NCV-NEV >= 2 and less than or equal to N.",
-4: "The maximum number of Arnoldi update iterations allowed "
"must be greater than zero.",
-5: " WHICH must be one of 'LM', 'SM', 'LR', 'SR', 'LI', 'SI'",
-6: "BMAT must be one of 'I' or 'G'.",
-7: "Length of private work array WORKL is not sufficient.",
-8: "Error return from LAPACK eigenvalue calculation;",
-9: "Starting vector is zero.",
-10: "IPARAM(7) must be 1,2,3,4.",
-11: "IPARAM(7) = 1 and BMAT = 'G' are incompatible.",
-12: "IPARAM(1) must be equal to 0 or 1.",
-13: "NEV and WHICH = 'BE' are incompatible.",
-9999: "Could not build an Arnoldi factorization. "
"IPARAM(5) returns the size of the current Arnoldi "
"factorization. The user is advised to check that "
"enough workspace and array storage has been allocated."
}
SNAUPD_ERRORS = DNAUPD_ERRORS
ZNAUPD_ERRORS = DNAUPD_ERRORS.copy()
ZNAUPD_ERRORS[-10] = "IPARAM(7) must be 1,2,3."
CNAUPD_ERRORS = ZNAUPD_ERRORS
DSAUPD_ERRORS = {
0: "Normal exit.",
1: "Maximum number of iterations taken. "
"All possible eigenvalues of OP has been found.",
2: "No longer an informational error. Deprecated starting with "
"release 2 of ARPACK.",
3: "No shifts could be applied during a cycle of the Implicitly "
"restarted Arnoldi iteration. One possibility is to increase "
"the size of NCV relative to NEV. ",
-1: "N must be positive.",
-2: "NEV must be positive.",
-3: "NCV must be greater than NEV and less than or equal to N.",
-4: "The maximum number of Arnoldi update iterations allowed "
"must be greater than zero.",
-5: "WHICH must be one of 'LM', 'SM', 'LA', 'SA' or 'BE'.",
-6: "BMAT must be one of 'I' or 'G'.",
-7: "Length of private work array WORKL is not sufficient.",
-8: "Error return from trid. eigenvalue calculation; "
"Informational error from LAPACK routine dsteqr .",
-9: "Starting vector is zero.",
-10: "IPARAM(7) must be 1,2,3,4,5.",
-11: "IPARAM(7) = 1 and BMAT = 'G' are incompatible.",
-12: "IPARAM(1) must be equal to 0 or 1.",
-13: "NEV and WHICH = 'BE' are incompatible. ",
-9999: "Could not build an Arnoldi factorization. "
"IPARAM(5) returns the size of the current Arnoldi "
"factorization. The user is advised to check that "
"enough workspace and array storage has been allocated.",
}
SSAUPD_ERRORS = DSAUPD_ERRORS
DNEUPD_ERRORS = {
0: "Normal exit.",
1: "The Schur form computed by LAPACK routine dlahqr "
"could not be reordered by LAPACK routine dtrsen. "
"Re-enter subroutine dneupd with IPARAM(5)NCV and "
"increase the size of the arrays DR and DI to have "
"dimension at least dimension NCV and allocate at least NCV "
"columns for Z. NOTE: Not necessary if Z and V share "
"the same space. Please notify the authors if this error"
"occurs.",
-1: "N must be positive.",
-2: "NEV must be positive.",
-3: "NCV-NEV >= 2 and less than or equal to N.",
-5: "WHICH must be one of 'LM', 'SM', 'LR', 'SR', 'LI', 'SI'",
-6: "BMAT must be one of 'I' or 'G'.",
-7: "Length of private work WORKL array is not sufficient.",
-8: "Error return from calculation of a real Schur form. "
"Informational error from LAPACK routine dlahqr .",
-9: "Error return from calculation of eigenvectors. "
"Informational error from LAPACK routine dtrevc.",
-10: "IPARAM(7) must be 1,2,3,4.",
-11: "IPARAM(7) = 1 and BMAT = 'G' are incompatible.",
-12: "HOWMNY = 'S' not yet implemented",
-13: "HOWMNY must be one of 'A' or 'P' if RVEC = .true.",
-14: "DNAUPD did not find any eigenvalues to sufficient "
"accuracy.",
-15: "DNEUPD got a different count of the number of converged "
"Ritz values than DNAUPD got. This indicates the user "
"probably made an error in passing data from DNAUPD to "
"DNEUPD or that the data was modified before entering "
"DNEUPD",
}
SNEUPD_ERRORS = DNEUPD_ERRORS.copy()
SNEUPD_ERRORS[1] = ("The Schur form computed by LAPACK routine slahqr "
"could not be reordered by LAPACK routine strsen . "
"Re-enter subroutine dneupd with IPARAM(5)=NCV and "
"increase the size of the arrays DR and DI to have "
"dimension at least dimension NCV and allocate at least "
"NCV columns for Z. NOTE: Not necessary if Z and V share "
"the same space. Please notify the authors if this error "
"occurs.")
SNEUPD_ERRORS[-14] = ("SNAUPD did not find any eigenvalues to sufficient "
"accuracy.")
SNEUPD_ERRORS[-15] = ("SNEUPD got a different count of the number of "
"converged Ritz values than SNAUPD got. This indicates "
"the user probably made an error in passing data from "
"SNAUPD to SNEUPD or that the data was modified before "
"entering SNEUPD")
ZNEUPD_ERRORS = {0: "Normal exit.",
1: "The Schur form computed by LAPACK routine csheqr "
"could not be reordered by LAPACK routine ztrsen. "
"Re-enter subroutine zneupd with IPARAM(5)=NCV and "
"increase the size of the array D to have "
"dimension at least dimension NCV and allocate at least "
"NCV columns for Z. NOTE: Not necessary if Z and V share "
"the same space. Please notify the authors if this error "
"occurs.",
-1: "N must be positive.",
-2: "NEV must be positive.",
-3: "NCV-NEV >= 1 and less than or equal to N.",
-5: "WHICH must be one of 'LM', 'SM', 'LR', 'SR', 'LI', 'SI'",
-6: "BMAT must be one of 'I' or 'G'.",
-7: "Length of private work WORKL array is not sufficient.",
-8: "Error return from LAPACK eigenvalue calculation. "
"This should never happened.",
-9: "Error return from calculation of eigenvectors. "
"Informational error from LAPACK routine ztrevc.",
-10: "IPARAM(7) must be 1,2,3",
-11: "IPARAM(7) = 1 and BMAT = 'G' are incompatible.",
-12: "HOWMNY = 'S' not yet implemented",
-13: "HOWMNY must be one of 'A' or 'P' if RVEC = .true.",
-14: "ZNAUPD did not find any eigenvalues to sufficient "
"accuracy.",
-15: "ZNEUPD got a different count of the number of "
"converged Ritz values than ZNAUPD got. This "
"indicates the user probably made an error in passing "
"data from ZNAUPD to ZNEUPD or that the data was "
"modified before entering ZNEUPD"
}
CNEUPD_ERRORS = ZNEUPD_ERRORS.copy()
CNEUPD_ERRORS[-14] = ("CNAUPD did not find any eigenvalues to sufficient "
"accuracy.")
CNEUPD_ERRORS[-15] = ("CNEUPD got a different count of the number of "
"converged Ritz values than CNAUPD got. This indicates "
"the user probably made an error in passing data from "
"CNAUPD to CNEUPD or that the data was modified before "
"entering CNEUPD")
DSEUPD_ERRORS = {
0: "Normal exit.",
-1: "N must be positive.",
-2: "NEV must be positive.",
-3: "NCV must be greater than NEV and less than or equal to N.",
-5: "WHICH must be one of 'LM', 'SM', 'LA', 'SA' or 'BE'.",
-6: "BMAT must be one of 'I' or 'G'.",
-7: "Length of private work WORKL array is not sufficient.",
-8: ("Error return from trid. eigenvalue calculation; "
"Information error from LAPACK routine dsteqr."),
-9: "Starting vector is zero.",
-10: "IPARAM(7) must be 1,2,3,4,5.",
-11: "IPARAM(7) = 1 and BMAT = 'G' are incompatible.",
-12: "NEV and WHICH = 'BE' are incompatible.",
-14: "DSAUPD did not find any eigenvalues to sufficient accuracy.",
-15: "HOWMNY must be one of 'A' or 'S' if RVEC = .true.",
-16: "HOWMNY = 'S' not yet implemented",
-17: ("DSEUPD got a different count of the number of converged "
"Ritz values than DSAUPD got. This indicates the user "
"probably made an error in passing data from DSAUPD to "
"DSEUPD or that the data was modified before entering "
"DSEUPD.")
}
SSEUPD_ERRORS = DSEUPD_ERRORS.copy()
SSEUPD_ERRORS[-14] = ("SSAUPD did not find any eigenvalues "
"to sufficient accuracy.")
SSEUPD_ERRORS[-17] = ("SSEUPD got a different count of the number of "
"converged "
"Ritz values than SSAUPD got. This indicates the user "
"probably made an error in passing data from SSAUPD to "
"SSEUPD or that the data was modified before entering "
"SSEUPD.")
_SAUPD_ERRORS = {'d': DSAUPD_ERRORS,
's': SSAUPD_ERRORS}
_NAUPD_ERRORS = {'d': DNAUPD_ERRORS,
's': SNAUPD_ERRORS,
'z': ZNAUPD_ERRORS,
'c': CNAUPD_ERRORS}
_SEUPD_ERRORS = {'d': DSEUPD_ERRORS,
's': SSEUPD_ERRORS}
_NEUPD_ERRORS = {'d': DNEUPD_ERRORS,
's': SNEUPD_ERRORS,
'z': ZNEUPD_ERRORS,
'c': CNEUPD_ERRORS}
# accepted values of parameter WHICH in _SEUPD
_SEUPD_WHICH = ['LM', 'SM', 'LA', 'SA', 'BE']
# accepted values of parameter WHICH in _NAUPD
_NEUPD_WHICH = ['LM', 'SM', 'LR', 'SR', 'LI', 'SI']
class ArpackError(RuntimeError):
"""
ARPACK error
"""
def __init__(self, info, infodict=_NAUPD_ERRORS):
msg = infodict.get(info, "Unknown error")
RuntimeError.__init__(self, "ARPACK error %d: %s" % (info, msg))
class ArpackNoConvergence(ArpackError):
"""
ARPACK iteration did not converge
Attributes
----------
eigenvalues : ndarray
Partial result. Converged eigenvalues.
eigenvectors : ndarray
Partial result. Converged eigenvectors.
"""
def __init__(self, msg, eigenvalues, eigenvectors):
ArpackError.__init__(self, -1, {-1: msg})
self.eigenvalues = eigenvalues
self.eigenvectors = eigenvectors
class _ArpackParams(object):
def __init__(self, n, k, tp, mode=1, sigma=None,
ncv=None, v0=None, maxiter=None, which="LM", tol=0):
if k <= 0:
raise ValueError("k must be positive, k=%d" % k)
if maxiter is None:
maxiter = n * 10
if maxiter <= 0:
raise ValueError("maxiter must be positive, maxiter=%d" % maxiter)
if tp not in 'fdFD':
raise ValueError("matrix type must be 'f', 'd', 'F', or 'D'")
if v0 is not None:
# ARPACK overwrites its initial resid, make a copy
self.resid = np.array(v0, copy=True)
info = 1
else:
# ARPACK will use a random initial vector.
self.resid = np.zeros(n, tp)
info = 0
if sigma is None:
#sigma not used
self.sigma = 0
else:
self.sigma = sigma
if ncv is None:
ncv = 2 * k + 1
ncv = min(ncv, n)
self.v = np.zeros((n, ncv), tp) # holds Ritz vectors
self.iparam = np.zeros(11, "int")
# set solver mode and parameters
ishfts = 1
self.mode = mode
self.iparam[0] = ishfts
self.iparam[2] = maxiter
self.iparam[3] = 1
self.iparam[6] = mode
self.n = n
self.tol = tol
self.k = k
self.maxiter = maxiter
self.ncv = ncv
self.which = which
self.tp = tp
self.info = info
self.converged = False
self.ido = 0
def _raise_no_convergence(self):
msg = "No convergence (%d iterations, %d/%d eigenvectors converged)"
k_ok = self.iparam[4]
num_iter = self.iparam[2]
try:
ev, vec = self.extract(True)
except ArpackError as err:
msg = "%s [%s]" % (msg, err)
ev = np.zeros((0,))
vec = np.zeros((self.n, 0))
k_ok = 0
raise ArpackNoConvergence(msg % (num_iter, k_ok, self.k), ev, vec)
class _SymmetricArpackParams(_ArpackParams):
def __init__(self, n, k, tp, matvec, mode=1, M_matvec=None,
Minv_matvec=None, sigma=None,
ncv=None, v0=None, maxiter=None, which="LM", tol=0):
# The following modes are supported:
# mode = 1:
# Solve the standard eigenvalue problem:
# A*x = lambda*x :
# A - symmetric
# Arguments should be
# matvec = left multiplication by A
# M_matvec = None [not used]
# Minv_matvec = None [not used]
#
# mode = 2:
# Solve the general eigenvalue problem:
# A*x = lambda*M*x
# A - symmetric
# M - symmetric positive definite
# Arguments should be
# matvec = left multiplication by A
# M_matvec = left multiplication by M
# Minv_matvec = left multiplication by M^-1
#
# mode = 3:
# Solve the general eigenvalue problem in shift-invert mode:
# A*x = lambda*M*x
# A - symmetric
# M - symmetric positive semi-definite
# Arguments should be
# matvec = None [not used]
# M_matvec = left multiplication by M
# or None, if M is the identity
# Minv_matvec = left multiplication by [A-sigma*M]^-1
#
# mode = 4:
# Solve the general eigenvalue problem in Buckling mode:
# A*x = lambda*AG*x
# A - symmetric positive semi-definite
# AG - symmetric indefinite
# Arguments should be
# matvec = left multiplication by A
# M_matvec = None [not used]
# Minv_matvec = left multiplication by [A-sigma*AG]^-1
#
# mode = 5:
# Solve the general eigenvalue problem in Cayley-transformed mode:
# A*x = lambda*M*x
# A - symmetric
# M - symmetric positive semi-definite
# Arguments should be
# matvec = left multiplication by A
# M_matvec = left multiplication by M
# or None, if M is the identity
# Minv_matvec = left multiplication by [A-sigma*M]^-1
if mode == 1:
if matvec is None:
raise ValueError("matvec must be specified for mode=1")
if M_matvec is not None:
raise ValueError("M_matvec cannot be specified for mode=1")
if Minv_matvec is not None:
raise ValueError("Minv_matvec cannot be specified for mode=1")
self.OP = matvec
self.B = lambda x: x
self.bmat = 'I'
elif mode == 2:
if matvec is None:
raise ValueError("matvec must be specified for mode=2")
if M_matvec is None:
raise ValueError("M_matvec must be specified for mode=2")
if Minv_matvec is None:
raise ValueError("Minv_matvec must be specified for mode=2")
self.OP = lambda x: Minv_matvec(matvec(x))
self.OPa = Minv_matvec
self.OPb = matvec
self.B = M_matvec
self.bmat = 'G'
elif mode == 3:
if matvec is not None:
raise ValueError("matvec must not be specified for mode=3")
if Minv_matvec is None:
raise ValueError("Minv_matvec must be specified for mode=3")
if M_matvec is None:
self.OP = Minv_matvec
self.OPa = Minv_matvec
self.B = lambda x: x
self.bmat = 'I'
else:
self.OP = lambda x: Minv_matvec(M_matvec(x))
self.OPa = Minv_matvec
self.B = M_matvec
self.bmat = 'G'
elif mode == 4:
if matvec is None:
raise ValueError("matvec must be specified for mode=4")
if M_matvec is not None:
raise ValueError("M_matvec must not be specified for mode=4")
if Minv_matvec is None:
raise ValueError("Minv_matvec must be specified for mode=4")
self.OPa = Minv_matvec
self.OP = lambda x: self.OPa(matvec(x))
self.B = matvec
self.bmat = 'G'
elif mode == 5:
if matvec is None:
raise ValueError("matvec must be specified for mode=5")
if Minv_matvec is None:
raise ValueError("Minv_matvec must be specified for mode=5")
self.OPa = Minv_matvec
self.A_matvec = matvec
if M_matvec is None:
self.OP = lambda x: Minv_matvec(matvec(x) + sigma * x)
self.B = lambda x: x
self.bmat = 'I'
else:
self.OP = lambda x: Minv_matvec(matvec(x)
+ sigma * M_matvec(x))
self.B = M_matvec
self.bmat = 'G'
else:
raise ValueError("mode=%i not implemented" % mode)
if which not in _SEUPD_WHICH:
raise ValueError("which must be one of %s"
% ' '.join(_SEUPD_WHICH))
if k >= n:
raise ValueError("k must be less than ndim(A), k=%d" % k)
_ArpackParams.__init__(self, n, k, tp, mode, sigma,
ncv, v0, maxiter, which, tol)
if self.ncv > n or self.ncv <= k:
raise ValueError("ncv must be k<ncv<=n, ncv=%s" % self.ncv)
# Use _aligned_zeros to work around a f2py bug in Numpy 1.9.1
self.workd = _aligned_zeros(3 * n, self.tp)
self.workl = _aligned_zeros(self.ncv * (self.ncv + 8), self.tp)
ltr = _type_conv[self.tp]
if ltr not in ["s", "d"]:
raise ValueError("Input matrix is not real-valued.")
self._arpack_solver = _arpack.__dict__[ltr + 'saupd']
self._arpack_extract = _arpack.__dict__[ltr + 'seupd']
self.iterate_infodict = _SAUPD_ERRORS[ltr]
self.extract_infodict = _SEUPD_ERRORS[ltr]
self.ipntr = np.zeros(11, "int")
def iterate(self):
self.ido, self.tol, self.resid, self.v, self.iparam, self.ipntr, self.info = \
self._arpack_solver(self.ido, self.bmat, self.which, self.k,
self.tol, self.resid, self.v, self.iparam,
self.ipntr, self.workd, self.workl, self.info)
xslice = slice(self.ipntr[0] - 1, self.ipntr[0] - 1 + self.n)
yslice = slice(self.ipntr[1] - 1, self.ipntr[1] - 1 + self.n)
if self.ido == -1:
# initialization
self.workd[yslice] = self.OP(self.workd[xslice])
elif self.ido == 1:
# compute y = Op*x
if self.mode == 1:
self.workd[yslice] = self.OP(self.workd[xslice])
elif self.mode == 2:
self.workd[xslice] = self.OPb(self.workd[xslice])
self.workd[yslice] = self.OPa(self.workd[xslice])
elif self.mode == 5:
Bxslice = slice(self.ipntr[2] - 1, self.ipntr[2] - 1 + self.n)
Ax = self.A_matvec(self.workd[xslice])
self.workd[yslice] = self.OPa(Ax + (self.sigma *
self.workd[Bxslice]))
else:
Bxslice = slice(self.ipntr[2] - 1, self.ipntr[2] - 1 + self.n)
self.workd[yslice] = self.OPa(self.workd[Bxslice])
elif self.ido == 2:
self.workd[yslice] = self.B(self.workd[xslice])
elif self.ido == 3:
raise ValueError("ARPACK requested user shifts. Assure ISHIFT==0")
else:
self.converged = True
if self.info == 0:
pass
elif self.info == 1:
self._raise_no_convergence()
else:
raise ArpackError(self.info, infodict=self.iterate_infodict)
def extract(self, return_eigenvectors):
rvec = return_eigenvectors
ierr = 0
howmny = 'A' # return all eigenvectors
sselect = np.zeros(self.ncv, 'int') # unused
d, z, ierr = self._arpack_extract(rvec, howmny, sselect, self.sigma,
self.bmat, self.which, self.k,
self.tol, self.resid, self.v,
self.iparam[0:7], self.ipntr,
self.workd[0:2 * self.n],
self.workl, ierr)
if ierr != 0:
raise ArpackError(ierr, infodict=self.extract_infodict)
k_ok = self.iparam[4]
d = d[:k_ok]
z = z[:, :k_ok]
if return_eigenvectors:
return d, z
else:
return d
class _UnsymmetricArpackParams(_ArpackParams):
def __init__(self, n, k, tp, matvec, mode=1, M_matvec=None,
Minv_matvec=None, sigma=None,
ncv=None, v0=None, maxiter=None, which="LM", tol=0):
# The following modes are supported:
# mode = 1:
# Solve the standard eigenvalue problem:
# A*x = lambda*x
# A - square matrix
# Arguments should be
# matvec = left multiplication by A
# M_matvec = None [not used]
# Minv_matvec = None [not used]
#
# mode = 2:
# Solve the generalized eigenvalue problem:
# A*x = lambda*M*x
# A - square matrix
# M - symmetric, positive semi-definite
# Arguments should be
# matvec = left multiplication by A
# M_matvec = left multiplication by M
# Minv_matvec = left multiplication by M^-1
#
# mode = 3,4:
# Solve the general eigenvalue problem in shift-invert mode:
# A*x = lambda*M*x
# A - square matrix
# M - symmetric, positive semi-definite
# Arguments should be
# matvec = None [not used]
# M_matvec = left multiplication by M
# or None, if M is the identity
# Minv_matvec = left multiplication by [A-sigma*M]^-1
# if A is real and mode==3, use the real part of Minv_matvec
# if A is real and mode==4, use the imag part of Minv_matvec
# if A is complex and mode==3,
# use real and imag parts of Minv_matvec
if mode == 1:
if matvec is None:
raise ValueError("matvec must be specified for mode=1")
if M_matvec is not None:
raise ValueError("M_matvec cannot be specified for mode=1")
if Minv_matvec is not None:
raise ValueError("Minv_matvec cannot be specified for mode=1")
self.OP = matvec
self.B = lambda x: x
self.bmat = 'I'
elif mode == 2:
if matvec is None:
raise ValueError("matvec must be specified for mode=2")
if M_matvec is None:
raise ValueError("M_matvec must be specified for mode=2")
if Minv_matvec is None:
raise ValueError("Minv_matvec must be specified for mode=2")
self.OP = lambda x: Minv_matvec(matvec(x))
self.OPa = Minv_matvec
self.OPb = matvec
self.B = M_matvec
self.bmat = 'G'
elif mode in (3, 4):
if matvec is None:
raise ValueError("matvec must be specified "
"for mode in (3,4)")
if Minv_matvec is None:
raise ValueError("Minv_matvec must be specified "
"for mode in (3,4)")
self.matvec = matvec
if tp in 'DF': # complex type
if mode == 3:
self.OPa = Minv_matvec
else:
raise ValueError("mode=4 invalid for complex A")
else: # real type
if mode == 3:
self.OPa = lambda x: np.real(Minv_matvec(x))
else:
self.OPa = lambda x: np.imag(Minv_matvec(x))
if M_matvec is None:
self.B = lambda x: x
self.bmat = 'I'
self.OP = self.OPa
else:
self.B = M_matvec
self.bmat = 'G'
self.OP = lambda x: self.OPa(M_matvec(x))
else:
raise ValueError("mode=%i not implemented" % mode)
if which not in _NEUPD_WHICH:
raise ValueError("Parameter which must be one of %s"
% ' '.join(_NEUPD_WHICH))
if k >= n - 1:
raise ValueError("k must be less than ndim(A)-1, k=%d" % k)
_ArpackParams.__init__(self, n, k, tp, mode, sigma,
ncv, v0, maxiter, which, tol)
if self.ncv > n or self.ncv <= k + 1:
raise ValueError("ncv must be k+1<ncv<=n, ncv=%s" % self.ncv)
# Use _aligned_zeros to work around a f2py bug in Numpy 1.9.1
self.workd = _aligned_zeros(3 * n, self.tp)
self.workl = _aligned_zeros(3 * self.ncv * (self.ncv + 2), self.tp)
ltr = _type_conv[self.tp]
self._arpack_solver = _arpack.__dict__[ltr + 'naupd']
self._arpack_extract = _arpack.__dict__[ltr + 'neupd']
self.iterate_infodict = _NAUPD_ERRORS[ltr]
self.extract_infodict = _NEUPD_ERRORS[ltr]
self.ipntr = np.zeros(14, "int")
if self.tp in 'FD':
# Use _aligned_zeros to work around a f2py bug in Numpy 1.9.1
self.rwork = _aligned_zeros(self.ncv, self.tp.lower())
else:
self.rwork = None
def iterate(self):
if self.tp in 'fd':
self.ido, self.tol, self.resid, self.v, self.iparam, self.ipntr, self.info =\
self._arpack_solver(self.ido, self.bmat, self.which, self.k,
self.tol, self.resid, self.v, self.iparam,
self.ipntr, self.workd, self.workl,
self.info)
else:
self.ido, self.tol, self.resid, self.v, self.iparam, self.ipntr, self.info =\
self._arpack_solver(self.ido, self.bmat, self.which, self.k,
self.tol, self.resid, self.v, self.iparam,
self.ipntr, self.workd, self.workl,
self.rwork, self.info)
xslice = slice(self.ipntr[0] - 1, self.ipntr[0] - 1 + self.n)
yslice = slice(self.ipntr[1] - 1, self.ipntr[1] - 1 + self.n)
if self.ido == -1:
# initialization
self.workd[yslice] = self.OP(self.workd[xslice])
elif self.ido == 1:
# compute y = Op*x
if self.mode in (1, 2):
self.workd[yslice] = self.OP(self.workd[xslice])
else:
Bxslice = slice(self.ipntr[2] - 1, self.ipntr[2] - 1 + self.n)
self.workd[yslice] = self.OPa(self.workd[Bxslice])
elif self.ido == 2:
self.workd[yslice] = self.B(self.workd[xslice])
elif self.ido == 3:
raise ValueError("ARPACK requested user shifts. Assure ISHIFT==0")
else:
self.converged = True
if self.info == 0:
pass
elif self.info == 1:
self._raise_no_convergence()
else:
raise ArpackError(self.info, infodict=self.iterate_infodict)
def extract(self, return_eigenvectors):
k, n = self.k, self.n
ierr = 0
howmny = 'A' # return all eigenvectors
sselect = np.zeros(self.ncv, 'int') # unused
sigmar = np.real(self.sigma)
sigmai = np.imag(self.sigma)
workev = np.zeros(3 * self.ncv, self.tp)
if self.tp in 'fd':
dr = np.zeros(k + 1, self.tp)
di = np.zeros(k + 1, self.tp)
zr = np.zeros((n, k + 1), self.tp)
dr, di, zr, ierr = \
self._arpack_extract(return_eigenvectors,
howmny, sselect, sigmar, sigmai, workev,
self.bmat, self.which, k, self.tol, self.resid,
self.v, self.iparam, self.ipntr,
self.workd, self.workl, self.info)
if ierr != 0:
raise ArpackError(ierr, infodict=self.extract_infodict)
nreturned = self.iparam[4] # number of good eigenvalues returned
# Build complex eigenvalues from real and imaginary parts
d = dr + 1.0j * di
# Arrange the eigenvectors: complex eigenvectors are stored as
# real,imaginary in consecutive columns
z = zr.astype(self.tp.upper())
# The ARPACK nonsymmetric real and double interface (s,d)naupd
# return eigenvalues and eigenvectors in real (float,double)
# arrays.
# Efficiency: this should check that return_eigenvectors == True
# before going through this construction.
if sigmai == 0:
i = 0
while i <= k:
# check if complex
if abs(d[i].imag) != 0:
# this is a complex conjugate pair with eigenvalues
# in consecutive columns
if i < k:
z[:, i] = zr[:, i] + 1.0j * zr[:, i + 1]
z[:, i + 1] = z[:, i].conjugate()
i += 1
else:
#last eigenvalue is complex: the imaginary part of
# the eigenvector has not been returned
#this can only happen if nreturned > k, so we'll
# throw out this case.
nreturned -= 1
i += 1
else:
# real matrix, mode 3 or 4, imag(sigma) is nonzero:
# see remark 3 in <s,d>neupd.f
# Build complex eigenvalues from real and imaginary parts
i = 0
while i <= k:
if abs(d[i].imag) == 0:
d[i] = np.dot(zr[:, i], self.matvec(zr[:, i]))
else:
if i < k:
z[:, i] = zr[:, i] + 1.0j * zr[:, i + 1]
z[:, i + 1] = z[:, i].conjugate()
d[i] = ((np.dot(zr[:, i],
self.matvec(zr[:, i]))
+ np.dot(zr[:, i + 1],
self.matvec(zr[:, i + 1])))
+ 1j * (np.dot(zr[:, i],
self.matvec(zr[:, i + 1]))
- np.dot(zr[:, i + 1],
self.matvec(zr[:, i]))))
d[i + 1] = d[i].conj()
i += 1
else:
#last eigenvalue is complex: the imaginary part of
# the eigenvector has not been returned
#this can only happen if nreturned > k, so we'll
# throw out this case.
nreturned -= 1
i += 1
# Now we have k+1 possible eigenvalues and eigenvectors
# Return the ones specified by the keyword "which"
if nreturned <= k:
# we got less or equal as many eigenvalues we wanted
d = d[:nreturned]
z = z[:, :nreturned]
else:
# we got one extra eigenvalue (likely a cc pair, but which?)
# cut at approx precision for sorting
rd = np.round(d, decimals=_ndigits[self.tp])
if self.which in ['LR', 'SR']:
ind = np.argsort(rd.real)
elif self.which in ['LI', 'SI']:
# for LI,SI ARPACK returns largest,smallest
# abs(imaginary) why?
ind = np.argsort(abs(rd.imag))
else:
ind = np.argsort(abs(rd))
if self.which in ['LR', 'LM', 'LI']:
d = d[ind[-k:]]
z = z[:, ind[-k:]]
if self.which in ['SR', 'SM', 'SI']:
d = d[ind[:k]]
z = z[:, ind[:k]]
else:
# complex is so much simpler...
d, z, ierr =\
self._arpack_extract(return_eigenvectors,
howmny, sselect, self.sigma, workev,
self.bmat, self.which, k, self.tol, self.resid,
self.v, self.iparam, self.ipntr,
self.workd, self.workl, self.rwork, ierr)
if ierr != 0:
raise ArpackError(ierr, infodict=self.extract_infodict)
k_ok = self.iparam[4]
d = d[:k_ok]
z = z[:, :k_ok]
if return_eigenvectors:
return d, z
else:
return d
def _aslinearoperator_with_dtype(m):
m = aslinearoperator(m)
if not hasattr(m, 'dtype'):
x = np.zeros(m.shape[1])
m.dtype = (m * x).dtype
return m
class SpLuInv(LinearOperator):
"""
SpLuInv:
helper class to repeatedly solve M*x=b
using a sparse LU-decopposition of M
"""
def __init__(self, M):
self.M_lu = splu(M)
self.shape = M.shape
self.dtype = M.dtype
self.isreal = not np.issubdtype(self.dtype, np.complexfloating)
def _matvec(self, x):
# careful here: splu.solve will throw away imaginary
# part of x if M is real
x = np.asarray(x)
if self.isreal and np.issubdtype(x.dtype, np.complexfloating):
return (self.M_lu.solve(np.real(x).astype(self.dtype))
+ 1j * self.M_lu.solve(np.imag(x).astype(self.dtype)))
else:
return self.M_lu.solve(x.astype(self.dtype))
class LuInv(LinearOperator):
"""
LuInv:
helper class to repeatedly solve M*x=b
using an LU-decomposition of M
"""
def __init__(self, M):
self.M_lu = lu_factor(M)
self.shape = M.shape
self.dtype = M.dtype
def _matvec(self, x):
return lu_solve(self.M_lu, x)
class IterInv(LinearOperator):
"""
IterInv:
helper class to repeatedly solve M*x=b
using an iterative method.
"""
def __init__(self, M, ifunc=gmres, tol=0):
if tol <= 0:
# when tol=0, ARPACK uses machine tolerance as calculated
# by LAPACK's _LAMCH function. We should match this
tol = 2 * np.finfo(M.dtype).eps
self.M = M
self.ifunc = ifunc
self.tol = tol
if hasattr(M, 'dtype'):
self.dtype = M.dtype
else:
x = np.zeros(M.shape[1])
self.dtype = (M * x).dtype
self.shape = M.shape
def _matvec(self, x):
b, info = self.ifunc(self.M, x, tol=self.tol)
if info != 0:
raise ValueError("Error in inverting M: function "
"%s did not converge (info = %i)."
% (self.ifunc.__name__, info))
return b
class IterOpInv(LinearOperator):
"""
IterOpInv:
helper class to repeatedly solve [A-sigma*M]*x = b
using an iterative method
"""
def __init__(self, A, M, sigma, ifunc=gmres, tol=0):
if tol <= 0:
# when tol=0, ARPACK uses machine tolerance as calculated
# by LAPACK's _LAMCH function. We should match this
tol = 2 * np.finfo(A.dtype).eps
self.A = A
self.M = M
self.sigma = sigma
self.ifunc = ifunc
self.tol = tol
def mult_func(x):
return A.matvec(x) - sigma * M.matvec(x)
def mult_func_M_None(x):
return A.matvec(x) - sigma * x
x = np.zeros(A.shape[1])
if M is None:
dtype = mult_func_M_None(x).dtype
self.OP = LinearOperator(self.A.shape,
mult_func_M_None,
dtype=dtype)
else:
dtype = mult_func(x).dtype
self.OP = LinearOperator(self.A.shape,
mult_func,
dtype=dtype)
self.shape = A.shape
def _matvec(self, x):
b, info = self.ifunc(self.OP, x, tol=self.tol)
if info != 0:
raise ValueError("Error in inverting [A-sigma*M]: function "
"%s did not converge (info = %i)."
% (self.ifunc.__name__, info))
return b
@property
def dtype(self):
return self.OP.dtype
def get_inv_matvec(M, symmetric=False, tol=0):
if isdense(M):
return LuInv(M).matvec
elif isspmatrix(M):
if isspmatrix_csr(M) and symmetric:
M = M.T
return SpLuInv(M).matvec
else:
return IterInv(M, tol=tol).matvec
def get_OPinv_matvec(A, M, sigma, symmetric=False, tol=0):
if sigma == 0:
return get_inv_matvec(A, symmetric=symmetric, tol=tol)
if M is None:
#M is the identity matrix
if isdense(A):
if (np.issubdtype(A.dtype, np.complexfloating)
or np.imag(sigma) == 0):
A = np.copy(A)
else:
A = A + 0j
A.flat[::A.shape[1] + 1] -= sigma
return LuInv(A).matvec
elif isspmatrix(A):
A = A - sigma * eye(A.shape[0])
if symmetric and isspmatrix_csr(A):
A = A.T
return SpLuInv(A.tocsc()).matvec
else:
return IterOpInv(_aslinearoperator_with_dtype(A),
M, sigma, tol=tol).matvec
else:
if ((not isdense(A) and not isspmatrix(A)) or
(not isdense(M) and not isspmatrix(M))):
return IterOpInv(_aslinearoperator_with_dtype(A),
_aslinearoperator_with_dtype(M),
sigma, tol=tol).matvec
elif isdense(A) or isdense(M):
return LuInv(A - sigma * M).matvec
else:
OP = A - sigma * M
if symmetric and isspmatrix_csr(OP):
OP = OP.T
return SpLuInv(OP.tocsc()).matvec
def eigs(A, k=6, M=None, sigma=None, which='LM', v0=None,
ncv=None, maxiter=None, tol=0, return_eigenvectors=True,
Minv=None, OPinv=None, OPpart=None):
"""
Find k eigenvalues and eigenvectors of the square matrix A.
Solves ``A * x[i] = w[i] * x[i]``, the standard eigenvalue problem
for w[i] eigenvalues with corresponding eigenvectors x[i].
If M is specified, solves ``A * x[i] = w[i] * M * x[i]``, the
generalized eigenvalue problem for w[i] eigenvalues
with corresponding eigenvectors x[i]
Parameters
----------
A : ndarray, sparse matrix or LinearOperator
An array, sparse matrix, or LinearOperator representing
the operation ``A * x``, where A is a real or complex square matrix.
k : int, optional
The number of eigenvalues and eigenvectors desired.
`k` must be smaller than N. It is not possible to compute all
eigenvectors of a matrix.
M : ndarray, sparse matrix or LinearOperator, optional
An array, sparse matrix, or LinearOperator representing
the operation M*x for the generalized eigenvalue problem
A * x = w * M * x.
M must represent a real, symmetric matrix if A is real, and must
represent a complex, hermitian matrix if A is complex. For best
results, the data type of M should be the same as that of A.
Additionally:
If `sigma` is None, M is positive definite
If sigma is specified, M is positive semi-definite
If sigma is None, eigs requires an operator to compute the solution
of the linear equation ``M * x = b``. This is done internally via a
(sparse) LU decomposition for an explicit matrix M, or via an
iterative solver for a general linear operator. Alternatively,
the user can supply the matrix or operator Minv, which gives
``x = Minv * b = M^-1 * b``.
sigma : real or complex, optional
Find eigenvalues near sigma using shift-invert mode. This requires
an operator to compute the solution of the linear system
``[A - sigma * M] * x = b``, where M is the identity matrix if
unspecified. This is computed internally via a (sparse) LU
decomposition for explicit matrices A & M, or via an iterative
solver if either A or M is a general linear operator.
Alternatively, the user can supply the matrix or operator OPinv,
which gives ``x = OPinv * b = [A - sigma * M]^-1 * b``.
For a real matrix A, shift-invert can either be done in imaginary
mode or real mode, specified by the parameter OPpart ('r' or 'i').
Note that when sigma is specified, the keyword 'which' (below)
refers to the shifted eigenvalues ``w'[i]`` where:
If A is real and OPpart == 'r' (default),
``w'[i] = 1/2 * [1/(w[i]-sigma) + 1/(w[i]-conj(sigma))]``.
If A is real and OPpart == 'i',
``w'[i] = 1/2i * [1/(w[i]-sigma) - 1/(w[i]-conj(sigma))]``.
If A is complex, ``w'[i] = 1/(w[i]-sigma)``.
v0 : ndarray, optional
Starting vector for iteration.
Default: random
ncv : int, optional
The number of Lanczos vectors generated
`ncv` must be greater than `k`; it is recommended that ``ncv > 2*k``.
Default: ``min(n, 2*k + 1)``
which : str, ['LM' | 'SM' | 'LR' | 'SR' | 'LI' | 'SI'], optional
Which `k` eigenvectors and eigenvalues to find:
'LM' : largest magnitude
'SM' : smallest magnitude
'LR' : largest real part
'SR' : smallest real part
'LI' : largest imaginary part
'SI' : smallest imaginary part
When sigma != None, 'which' refers to the shifted eigenvalues w'[i]
(see discussion in 'sigma', above). ARPACK is generally better
at finding large values than small values. If small eigenvalues are
desired, consider using shift-invert mode for better performance.
maxiter : int, optional
Maximum number of Arnoldi update iterations allowed
Default: ``n*10``
tol : float, optional
Relative accuracy for eigenvalues (stopping criterion)
The default value of 0 implies machine precision.
return_eigenvectors : bool, optional
Return eigenvectors (True) in addition to eigenvalues
Minv : ndarray, sparse matrix or LinearOperator, optional
See notes in M, above.
OPinv : ndarray, sparse matrix or LinearOperator, optional
See notes in sigma, above.
OPpart : {'r' or 'i'}, optional
See notes in sigma, above
Returns
-------
w : ndarray
Array of k eigenvalues.
v : ndarray
An array of `k` eigenvectors.
``v[:, i]`` is the eigenvector corresponding to the eigenvalue w[i].
Raises
------
ArpackNoConvergence
When the requested convergence is not obtained.
The currently converged eigenvalues and eigenvectors can be found
as ``eigenvalues`` and ``eigenvectors`` attributes of the exception
object.
See Also
--------
eigsh : eigenvalues and eigenvectors for symmetric matrix A
svds : singular value decomposition for a matrix A
Notes
-----
This function is a wrapper to the ARPACK [1]_ SNEUPD, DNEUPD, CNEUPD,
ZNEUPD, functions which use the Implicitly Restarted Arnoldi Method to
find the eigenvalues and eigenvectors [2]_.
References
----------
.. [1] ARPACK Software, http://www.caam.rice.edu/software/ARPACK/
.. [2] R. B. Lehoucq, D. C. Sorensen, and C. Yang, ARPACK USERS GUIDE:
Solution of Large Scale Eigenvalue Problems by Implicitly Restarted
Arnoldi Methods. SIAM, Philadelphia, PA, 1998.
Examples
--------
Find 6 eigenvectors of the identity matrix:
>>> import scipy.sparse as sparse
>>> id = np.eye(13)
>>> vals, vecs = sparse.linalg.eigs(id, k=6)
>>> vals
array([ 1.+0.j, 1.+0.j, 1.+0.j, 1.+0.j, 1.+0.j, 1.+0.j])
>>> vecs.shape
(13, 6)
"""
if A.shape[0] != A.shape[1]:
raise ValueError('expected square matrix (shape=%s)' % (A.shape,))
if M is not None:
if M.shape != A.shape:
raise ValueError('wrong M dimensions %s, should be %s'
% (M.shape, A.shape))
if np.dtype(M.dtype).char.lower() != np.dtype(A.dtype).char.lower():
import warnings
warnings.warn('M does not have the same type precision as A. '
'This may adversely affect ARPACK convergence')
n = A.shape[0]
if k <= 0 or k >= n:
raise ValueError("k=%d must be between 1 and ndim(A)-1=%d"
% (k, n - 1))
if sigma is None:
matvec = _aslinearoperator_with_dtype(A).matvec
if OPinv is not None:
raise ValueError("OPinv should not be specified "
"with sigma = None.")
if OPpart is not None:
raise ValueError("OPpart should not be specified with "
"sigma = None or complex A")
if M is None:
#standard eigenvalue problem
mode = 1
M_matvec = None
Minv_matvec = None
if Minv is not None:
raise ValueError("Minv should not be "
"specified with M = None.")
else:
#general eigenvalue problem
mode = 2
if Minv is None:
Minv_matvec = get_inv_matvec(M, symmetric=True, tol=tol)
else:
Minv = _aslinearoperator_with_dtype(Minv)
Minv_matvec = Minv.matvec
M_matvec = _aslinearoperator_with_dtype(M).matvec
else:
#sigma is not None: shift-invert mode
if np.issubdtype(A.dtype, np.complexfloating):
if OPpart is not None:
raise ValueError("OPpart should not be specified "
"with sigma=None or complex A")
mode = 3
elif OPpart is None or OPpart.lower() == 'r':
mode = 3
elif OPpart.lower() == 'i':
if np.imag(sigma) == 0:
raise ValueError("OPpart cannot be 'i' if sigma is real")
mode = 4
else:
raise ValueError("OPpart must be one of ('r','i')")
matvec = _aslinearoperator_with_dtype(A).matvec
if Minv is not None:
raise ValueError("Minv should not be specified when sigma is")
if OPinv is None:
Minv_matvec = get_OPinv_matvec(A, M, sigma,
symmetric=False, tol=tol)
else:
OPinv = _aslinearoperator_with_dtype(OPinv)
Minv_matvec = OPinv.matvec
if M is None:
M_matvec = None
else:
M_matvec = _aslinearoperator_with_dtype(M).matvec
params = _UnsymmetricArpackParams(n, k, A.dtype.char, matvec, mode,
M_matvec, Minv_matvec, sigma,
ncv, v0, maxiter, which, tol)
while not params.converged:
params.iterate()
return params.extract(return_eigenvectors)
[docs]def eigsh(A, k=6, M=None, sigma=None, which='LM', v0=None,
ncv=None, maxiter=None, tol=0, return_eigenvectors=True,
Minv=None, OPinv=None, mode='normal'):
"""
Find k eigenvalues and eigenvectors of the real symmetric square matrix
or complex hermitian matrix A.
Solves ``A * x[i] = w[i] * x[i]``, the standard eigenvalue problem for
w[i] eigenvalues with corresponding eigenvectors x[i].
If M is specified, solves ``A * x[i] = w[i] * M * x[i]``, the
generalized eigenvalue problem for w[i] eigenvalues
with corresponding eigenvectors x[i]
Parameters
----------
A : An N x N matrix, array, sparse matrix, or LinearOperator representing
the operation A * x, where A is a real symmetric matrix
For buckling mode (see below) A must additionally be positive-definite
k : int, optional
The number of eigenvalues and eigenvectors desired.
`k` must be smaller than N. It is not possible to compute all
eigenvectors of a matrix.
Returns
-------
w : array
Array of k eigenvalues
v : array
An array representing the `k` eigenvectors. The column ``v[:, i]`` is
the eigenvector corresponding to the eigenvalue ``w[i]``.
Other Parameters
----------------
M : An N x N matrix, array, sparse matrix, or linear operator representing
the operation M * x for the generalized eigenvalue problem
A * x = w * M * x.
M must represent a real, symmetric matrix if A is real, and must
represent a complex, hermitian matrix if A is complex. For best
results, the data type of M should be the same as that of A.
Additionally:
If sigma is None, M is symmetric positive definite
If sigma is specified, M is symmetric positive semi-definite
In buckling mode, M is symmetric indefinite.
If sigma is None, eigsh requires an operator to compute the solution
of the linear equation ``M * x = b``. This is done internally via a
(sparse) LU decomposition for an explicit matrix M, or via an
iterative solver for a general linear operator. Alternatively,
the user can supply the matrix or operator Minv, which gives
``x = Minv * b = M^-1 * b``.
sigma : real
Find eigenvalues near sigma using shift-invert mode. This requires
an operator to compute the solution of the linear system
`[A - sigma * M] x = b`, where M is the identity matrix if
unspecified. This is computed internally via a (sparse) LU
decomposition for explicit matrices A & M, or via an iterative
solver if either A or M is a general linear operator.
Alternatively, the user can supply the matrix or operator OPinv,
which gives ``x = OPinv * b = [A - sigma * M]^-1 * b``.
Note that when sigma is specified, the keyword 'which' refers to
the shifted eigenvalues ``w'[i]`` where:
if mode == 'normal', ``w'[i] = 1 / (w[i] - sigma)``.
if mode == 'cayley', ``w'[i] = (w[i] + sigma) / (w[i] - sigma)``.
if mode == 'buckling', ``w'[i] = w[i] / (w[i] - sigma)``.
(see further discussion in 'mode' below)
v0 : ndarray, optional
Starting vector for iteration.
Default: random
ncv : int, optional
The number of Lanczos vectors generated ncv must be greater than k and
smaller than n; it is recommended that ``ncv > 2*k``.
Default: ``min(n, 2*k + 1)``
which : str ['LM' | 'SM' | 'LA' | 'SA' | 'BE']
If A is a complex hermitian matrix, 'BE' is invalid.
Which `k` eigenvectors and eigenvalues to find:
'LM' : Largest (in magnitude) eigenvalues
'SM' : Smallest (in magnitude) eigenvalues
'LA' : Largest (algebraic) eigenvalues
'SA' : Smallest (algebraic) eigenvalues
'BE' : Half (k/2) from each end of the spectrum
When k is odd, return one more (k/2+1) from the high end.
When sigma != None, 'which' refers to the shifted eigenvalues ``w'[i]``
(see discussion in 'sigma', above). ARPACK is generally better
at finding large values than small values. If small eigenvalues are
desired, consider using shift-invert mode for better performance.
maxiter : int, optional
Maximum number of Arnoldi update iterations allowed
Default: ``n*10``
tol : float
Relative accuracy for eigenvalues (stopping criterion).
The default value of 0 implies machine precision.
Minv : N x N matrix, array, sparse matrix, or LinearOperator
See notes in M, above
OPinv : N x N matrix, array, sparse matrix, or LinearOperator
See notes in sigma, above.
return_eigenvectors : bool
Return eigenvectors (True) in addition to eigenvalues
mode : string ['normal' | 'buckling' | 'cayley']
Specify strategy to use for shift-invert mode. This argument applies
only for real-valued A and sigma != None. For shift-invert mode,
ARPACK internally solves the eigenvalue problem
``OP * x'[i] = w'[i] * B * x'[i]``
and transforms the resulting Ritz vectors x'[i] and Ritz values w'[i]
into the desired eigenvectors and eigenvalues of the problem
``A * x[i] = w[i] * M * x[i]``.
The modes are as follows:
'normal' :
OP = [A - sigma * M]^-1 * M,
B = M,
w'[i] = 1 / (w[i] - sigma)
'buckling' :
OP = [A - sigma * M]^-1 * A,
B = A,
w'[i] = w[i] / (w[i] - sigma)
'cayley' :
OP = [A - sigma * M]^-1 * [A + sigma * M],
B = M,
w'[i] = (w[i] + sigma) / (w[i] - sigma)
The choice of mode will affect which eigenvalues are selected by
the keyword 'which', and can also impact the stability of
convergence (see [2] for a discussion)
Raises
------
ArpackNoConvergence
When the requested convergence is not obtained.
The currently converged eigenvalues and eigenvectors can be found
as ``eigenvalues`` and ``eigenvectors`` attributes of the exception
object.
See Also
--------
eigs : eigenvalues and eigenvectors for a general (nonsymmetric) matrix A
svds : singular value decomposition for a matrix A
Notes
-----
This function is a wrapper to the ARPACK [1]_ SSEUPD and DSEUPD
functions which use the Implicitly Restarted Lanczos Method to
find the eigenvalues and eigenvectors [2]_.
References
----------
.. [1] ARPACK Software, http://www.caam.rice.edu/software/ARPACK/
.. [2] R. B. Lehoucq, D. C. Sorensen, and C. Yang, ARPACK USERS GUIDE:
Solution of Large Scale Eigenvalue Problems by Implicitly Restarted
Arnoldi Methods. SIAM, Philadelphia, PA, 1998.
Examples
--------
>>> import scipy.sparse as sparse
>>> id = np.eye(13)
>>> vals, vecs = sparse.linalg.eigsh(id, k=6)
>>> vals
array([ 1.+0.j, 1.+0.j, 1.+0.j, 1.+0.j, 1.+0.j, 1.+0.j])
>>> vecs.shape
(13, 6)
"""
# complex hermitian matrices should be solved with eigs
if np.issubdtype(A.dtype, np.complexfloating):
if mode != 'normal':
raise ValueError("mode=%s cannot be used with "
"complex matrix A" % mode)
if which == 'BE':
raise ValueError("which='BE' cannot be used with complex matrix A")
elif which == 'LA':
which = 'LR'
elif which == 'SA':
which = 'SR'
ret = eigs(A, k, M=M, sigma=sigma, which=which, v0=v0,
ncv=ncv, maxiter=maxiter, tol=tol,
return_eigenvectors=return_eigenvectors, Minv=Minv,
OPinv=OPinv)
if return_eigenvectors:
return ret[0].real, ret[1]
else:
return ret.real
if A.shape[0] != A.shape[1]:
raise ValueError('expected square matrix (shape=%s)' % (A.shape,))
if M is not None:
if M.shape != A.shape:
raise ValueError('wrong M dimensions %s, should be %s'
% (M.shape, A.shape))
if np.dtype(M.dtype).char.lower() != np.dtype(A.dtype).char.lower():
import warnings
warnings.warn('M does not have the same type precision as A. '
'This may adversely affect ARPACK convergence')
n = A.shape[0]
if k <= 0 or k >= n:
raise ValueError("k must be between 1 and the order of the "
"square input matrix.")
if sigma is None:
A = _aslinearoperator_with_dtype(A)
matvec = A.matvec
if OPinv is not None:
raise ValueError("OPinv should not be specified "
"with sigma = None.")
if M is None:
#standard eigenvalue problem
mode = 1
M_matvec = None
Minv_matvec = None
if Minv is not None:
raise ValueError("Minv should not be "
"specified with M = None.")
else:
#general eigenvalue problem
mode = 2
if Minv is None:
Minv_matvec = get_inv_matvec(M, symmetric=True, tol=tol)
else:
Minv = _aslinearoperator_with_dtype(Minv)
Minv_matvec = Minv.matvec
M_matvec = _aslinearoperator_with_dtype(M).matvec
else:
# sigma is not None: shift-invert mode
if Minv is not None:
raise ValueError("Minv should not be specified when sigma is")
# normal mode
if mode == 'normal':
mode = 3
matvec = None
if OPinv is None:
Minv_matvec = get_OPinv_matvec(A, M, sigma,
symmetric=True, tol=tol)
else:
OPinv = _aslinearoperator_with_dtype(OPinv)
Minv_matvec = OPinv.matvec
if M is None:
M_matvec = None
else:
M = _aslinearoperator_with_dtype(M)
M_matvec = M.matvec
# buckling mode
elif mode == 'buckling':
mode = 4
if OPinv is None:
Minv_matvec = get_OPinv_matvec(A, M, sigma,
symmetric=True, tol=tol)
else:
Minv_matvec = _aslinearoperator_with_dtype(OPinv).matvec
matvec = _aslinearoperator_with_dtype(A).matvec
M_matvec = None
# cayley-transform mode
elif mode == 'cayley':
mode = 5
matvec = _aslinearoperator_with_dtype(A).matvec
if OPinv is None:
Minv_matvec = get_OPinv_matvec(A, M, sigma,
symmetric=True, tol=tol)
else:
Minv_matvec = _aslinearoperator_with_dtype(OPinv).matvec
if M is None:
M_matvec = None
else:
M_matvec = _aslinearoperator_with_dtype(M).matvec
# unrecognized mode
else:
raise ValueError("unrecognized mode '%s'" % mode)
params = _SymmetricArpackParams(n, k, A.dtype.char, matvec, mode,
M_matvec, Minv_matvec, sigma,
ncv, v0, maxiter, which, tol)
while not params.converged:
params.iterate()
return params.extract(return_eigenvectors)
def _augmented_orthonormal_cols(x, k):
# extract the shape of the x array
n, m = x.shape
# create the expanded array and copy x into it
y = np.empty((n, m+k), dtype=x.dtype)
y[:, :m] = x
# do some modified gram schmidt to add k random orthonormal vectors
for i in range(k):
# sample a random initial vector
v = np.random.randn(n)
if np.iscomplexobj(x):
v = v + 1j*np.random.randn(n)
# subtract projections onto the existing unit length vectors
for j in range(m+i):
u = y[:, j]
v -= (np.dot(v, u.conj()) / np.dot(u, u.conj())) * u
# normalize v
v /= np.sqrt(np.dot(v, v.conj()))
# add v into the output array
y[:, m+i] = v
# return the expanded array
return y
def _augmented_orthonormal_rows(x, k):
return _augmented_orthonormal_cols(x.T, k).T
def _herm(x):
return x.T.conj()
def svds(A, k=6, ncv=None, tol=0, which='LM', v0=None,
maxiter=None, return_singular_vectors=True):
"""Compute the largest k singular values/vectors for a sparse matrix.
Parameters
----------
A : {sparse matrix, LinearOperator}
Array to compute the SVD on, of shape (M, N)
k : int, optional
Number of singular values and vectors to compute.
Must be 1 <= k < min(A.shape).
ncv : int, optional
The number of Lanczos vectors generated
ncv must be greater than k+1 and smaller than n;
it is recommended that ncv > 2*k
Default: ``min(n, 2*k + 1)``
tol : float, optional
Tolerance for singular values. Zero (default) means machine precision.
which : str, ['LM' | 'SM'], optional
Which `k` singular values to find:
- 'LM' : largest singular values
- 'SM' : smallest singular values
.. versionadded:: 0.12.0
v0 : ndarray, optional
Starting vector for iteration, of length min(A.shape). Should be an
(approximate) left singular vector if N > M and a right singular
vector otherwise.
Default: random
.. versionadded:: 0.12.0
maxiter : int, optional
Maximum number of iterations.
.. versionadded:: 0.12.0
return_singular_vectors : bool or str, optional
- True: return singular vectors (True) in addition to singular values.
.. versionadded:: 0.12.0
- "u": only return the u matrix, without computing vh (if N > M).
- "vh": only return the vh matrix, without computing u (if N <= M).
.. versionadded:: 0.16.0
Returns
-------
u : ndarray, shape=(M, k)
Unitary matrix having left singular vectors as columns.
If `return_singular_vectors` is "vh", this variable is not computed,
and None is returned instead.
s : ndarray, shape=(k,)
The singular values.
vt : ndarray, shape=(k, N)
Unitary matrix having right singular vectors as rows.
If `return_singular_vectors` is "u", this variable is not computed,
and None is returned instead.
Notes
-----
This is a naive implementation using ARPACK as an eigensolver
on A.H * A or A * A.H, depending on which one is more efficient.
"""
if not (isinstance(A, LinearOperator) or isspmatrix(A)):
A = np.asarray(A)
n, m = A.shape
if k <= 0 or k >= min(n, m):
raise ValueError("k must be between 1 and min(A.shape), k=%d" % k)
if isinstance(A, LinearOperator):
if n > m:
X_dot = A.matvec
X_matmat = A.matmat
XH_dot = A.rmatvec
else:
X_dot = A.rmatvec
XH_dot = A.matvec
dtype = getattr(A, 'dtype', None)
if dtype is None:
dtype = A.dot(np.zeros([m,1])).dtype
# A^H * V; works around lack of LinearOperator.adjoint.
# XXX This can be slow!
def X_matmat(V):
out = np.empty((V.shape[1], m), dtype=dtype)
for i, col in enumerate(V.T):
out[i, :] = A.rmatvec(col.reshape(-1, 1)).T
return out.T
else:
if n > m:
X_dot = X_matmat = A.dot
XH_dot = _herm(A).dot
else:
XH_dot = A.dot
X_dot = X_matmat = _herm(A).dot
def matvec_XH_X(x):
return XH_dot(X_dot(x))
XH_X = LinearOperator(matvec=matvec_XH_X, dtype=A.dtype,
shape=(min(A.shape), min(A.shape)))
# Get a low rank approximation of the implicitly defined gramian matrix.
# This is not a stable way to approach the problem.
eigvals, eigvec = eigsh(XH_X, k=k, tol=tol ** 2, maxiter=maxiter,
ncv=ncv, which=which, v0=v0)
# In 'LM' mode try to be clever about small eigenvalues.
# Otherwise in 'SM' mode do not try to be clever.
if which == 'LM':
# Gramian matrices have real non-negative eigenvalues.
eigvals = np.maximum(eigvals.real, 0)
# Use the sophisticated detection of small eigenvalues from pinvh.
t = eigvec.dtype.char.lower()
factor = {'f': 1E3, 'd': 1E6}
cond = factor[t] * np.finfo(t).eps
cutoff = cond * np.max(eigvals)
# Get a mask indicating which eigenpairs are not degenerately tiny,
# and create the re-ordered array of thresholded singular values.
above_cutoff = (eigvals > cutoff)
nlarge = above_cutoff.sum()
nsmall = k - nlarge
slarge = np.sqrt(eigvals[above_cutoff])
s = np.zeros_like(eigvals)
s[:nlarge] = slarge
if not return_singular_vectors:
return s
if n > m:
vlarge = eigvec[:, above_cutoff]
ularge = X_matmat(vlarge) / slarge if return_singular_vectors != 'vh' else None
vhlarge = _herm(vlarge)
else:
ularge = eigvec[:, above_cutoff]
vhlarge = _herm(X_matmat(ularge) / slarge) if return_singular_vectors != 'u' else None
u = _augmented_orthonormal_cols(ularge, nsmall) if ularge is not None else None
vh = _augmented_orthonormal_rows(vhlarge, nsmall) if vhlarge is not None else None
elif which == 'SM':
s = np.sqrt(eigvals)
if not return_singular_vectors:
return s
if n > m:
v = eigvec
u = X_matmat(v) / s if return_singular_vectors != 'vh' else None
vh = _herm(v)
else:
u = eigvec
vh = _herm(X_matmat(u) / s) if return_singular_vectors != 'u' else None
else:
raise ValueError("which must be either 'LM' or 'SM'.")
return u, s, vh
