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#
# Author: Pearu Peterson, March 2002
#
# w/ additions by Travis Oliphant, March 2002
# and Jake Vanderplas, August 2012
from __future__ import division, print_function, absolute_import
import warnings
import numpy as np
from numpy import atleast_1d, atleast_2d
from .flinalg import get_flinalg_funcs
from .lapack import get_lapack_funcs, _compute_lwork
from .misc import LinAlgError, _datacopied
from .decomp import _asarray_validated
from . import decomp, decomp_svd
from ._solve_toeplitz import levinson
__all__ = ['solve', 'solve_triangular', 'solveh_banded', 'solve_banded',
'solve_toeplitz', 'solve_circulant', 'inv', 'det', 'lstsq',
'pinv', 'pinv2', 'pinvh', 'matrix_balance']
# Linear equations
def solve(a, b, sym_pos=False, lower=False, overwrite_a=False,
overwrite_b=False, debug=None, check_finite=True, assume_a='gen',
transposed=False):
"""
Solves the linear equation set ``a * x = b`` for the unknown ``x``
for square ``a`` matrix.
If the data matrix is known to be a particular type then supplying the
corresponding string to ``assume_a`` key chooses the dedicated solver.
The available options are
=================== ========
generic matrix 'gen'
symmetric 'sym'
hermitian 'her'
positive definite 'pos'
=================== ========
If omitted, ``'gen'`` is the default structure.
The datatype of the arrays define which solver is called regardless
of the values. In other words, even when the complex array entries have
precisely zero imaginary parts, the complex solver will be called based
on the data type of the array.
Parameters
----------
a : (N, N) array_like
Square input data
b : (N, NRHS) array_like
Input data for the right hand side.
sym_pos : bool, optional
Assume `a` is symmetric and positive definite. This key is deprecated
and assume_a = 'pos' keyword is recommended instead. The functionality
is the same. It will be removed in the future.
lower : bool, optional
If True, only the data contained in the lower triangle of `a`. Default
is to use upper triangle. (ignored for ``'gen'``)
overwrite_a : bool, optional
Allow overwriting data in `a` (may enhance performance).
Default is False.
overwrite_b : bool, optional
Allow overwriting data in `b` (may enhance performance).
Default is False.
check_finite : bool, optional
Whether to check that the input matrices contain only finite numbers.
Disabling may give a performance gain, but may result in problems
(crashes, non-termination) if the inputs do contain infinities or NaNs.
assume_a : str, optional
Valid entries are explained above.
transposed: bool, optional
If True, depending on the data type ``a^T x = b`` or ``a^H x = b`` is
solved (only taken into account for ``'gen'``).
Returns
-------
x : (N, NRHS) ndarray
The solution array.
Raises
------
ValueError
If size mismatches detected or input a is not square.
LinAlgError
If the matrix is singular.
RuntimeWarning
If an ill-conditioned input a is detected.
Examples
--------
Given `a` and `b`, solve for `x`:
>>> a = np.array([[3, 2, 0], [1, -1, 0], [0, 5, 1]])
>>> b = np.array([2, 4, -1])
>>> from scipy import linalg
>>> x = linalg.solve(a, b)
>>> x
array([ 2., -2., 9.])
>>> np.dot(a, x) == b
array([ True, True, True], dtype=bool)
Notes
-----
If the input b matrix is a 1D array with N elements, when supplied
together with an NxN input a, it is assumed as a valid column vector
despite the apparent size mismatch. This is compatible with the
numpy.dot() behavior and the returned result is still 1D array.
The generic, symmetric, hermitian and positive definite solutions are
obtained via calling ?GESVX, ?SYSVX, ?HESVX, and ?POSVX routines of
LAPACK respectively.
"""
# Flags for 1D or nD right hand side
b_is_1D = False
b_is_ND = False
a1 = atleast_2d(_asarray_validated(a, check_finite=check_finite))
b1 = atleast_1d(_asarray_validated(b, check_finite=check_finite))
n = a1.shape[0]
overwrite_a = overwrite_a or _datacopied(a1, a)
overwrite_b = overwrite_b or _datacopied(b1, b)
if a1.shape[0] != a1.shape[1]:
raise ValueError('Input a needs to be a square matrix.')
if n != b1.shape[0]:
# Last chance to catch 1x1 scalar a and 1D b arrays
if not (n == 1 and b1.size != 0):
raise ValueError('Input b has to have same number of rows as '
'input a')
# accomodate empty arrays
if b1.size == 0:
return np.asfortranarray(b1.copy())
# regularize 1D b arrays to 2D and catch nD RHS arrays
if b1.ndim == 1:
if n == 1:
b1 = b1[None, :]
else:
b1 = b1[:, None]
b_is_1D = True
elif b1.ndim > 2:
b_is_ND = True
r_or_c = complex if np.iscomplexobj(a1) else float
if assume_a in ('gen', 'sym', 'her', 'pos'):
_structure = assume_a
else:
raise ValueError('{} is not a recognized matrix structure'
''.format(assume_a))
# Deprecate keyword "debug"
if debug is not None:
warnings.warn('Use of the "debug" keyword is deprecated '
'and this keyword will be removed in the future '
'versions of SciPy.', DeprecationWarning)
# Backwards compatibility - old keyword.
if sym_pos:
assume_a = 'pos'
if _structure == 'gen':
gesvx = get_lapack_funcs('gesvx', (a1, b1))
trans_conj = 'N'
if transposed:
trans_conj = 'T' if r_or_c is float else 'H'
(_, _, _, _, _, _, _,
x, rcond, _, _, info) = gesvx(a1, b1,
trans=trans_conj,
overwrite_a=overwrite_a,
overwrite_b=overwrite_b
)
elif _structure == 'sym':
sysvx, sysvx_lw = get_lapack_funcs(('sysvx', 'sysvx_lwork'), (a1, b1))
lwork = _compute_lwork(sysvx_lw, n, lower)
_, _, _, _, x, rcond, _, _, info = sysvx(a1, b1, lwork=lwork,
lower=lower,
overwrite_a=overwrite_a,
overwrite_b=overwrite_b
)
elif _structure == 'her':
hesvx, hesvx_lw = get_lapack_funcs(('hesvx', 'hesvx_lwork'), (a1, b1))
lwork = _compute_lwork(hesvx_lw, n, lower)
_, _, x, rcond, _, _, info = hesvx(a1, b1, lwork=lwork,
lower=lower,
overwrite_a=overwrite_a,
overwrite_b=overwrite_b
)
else:
posvx = get_lapack_funcs('posvx', (a1, b1))
_, _, _, _, _, x, rcond, _, _, info = posvx(a1, b1,
lower=lower,
overwrite_a=overwrite_a,
overwrite_b=overwrite_b
)
# Unlike ?xxSV, ?xxSVX writes the solution x to a separate array, and
# overwrites b with its scaled version which is thrown away. Thus, the
# solution does not admit the same shape with the original b. For
# backwards compatibility, we reshape it manually.
if b_is_1D:
x = x.ravel()
if b_is_ND:
x = x.reshape(*b1.shape, order='F')
if info < 0:
raise ValueError('LAPACK reported an illegal value in {}-th argument'
'.'.format(-info))
elif info == 0:
return x
elif 0 < info <= n:
raise LinAlgError('Matrix is singular.')
elif info > n:
warnings.warn('scipy.linalg.solve\nIll-conditioned matrix detected.'
' Result is not guaranteed to be accurate.\nReciprocal'
' condition number: {}'.format(rcond), RuntimeWarning)
return x
def solve_triangular(a, b, trans=0, lower=False, unit_diagonal=False,
overwrite_b=False, debug=None, check_finite=True):
"""
Solve the equation `a x = b` for `x`, assuming a is a triangular matrix.
Parameters
----------
a : (M, M) array_like
A triangular matrix
b : (M,) or (M, N) array_like
Right-hand side matrix in `a x = b`
lower : bool, optional
Use only data contained in the lower triangle of `a`.
Default is to use upper triangle.
trans : {0, 1, 2, 'N', 'T', 'C'}, optional
Type of system to solve:
======== =========
trans system
======== =========
0 or 'N' a x = b
1 or 'T' a^T x = b
2 or 'C' a^H x = b
======== =========
unit_diagonal : bool, optional
If True, diagonal elements of `a` are assumed to be 1 and
will not be referenced.
overwrite_b : bool, optional
Allow overwriting data in `b` (may enhance performance)
check_finite : bool, optional
Whether to check that the input matrices contain only finite numbers.
Disabling may give a performance gain, but may result in problems
(crashes, non-termination) if the inputs do contain infinities or NaNs.
Returns
-------
x : (M,) or (M, N) ndarray
Solution to the system `a x = b`. Shape of return matches `b`.
Raises
------
LinAlgError
If `a` is singular
Notes
-----
.. versionadded:: 0.9.0
Examples
--------
Solve the lower triangular system a x = b, where::
[3 0 0 0] [4]
a = [2 1 0 0] b = [2]
[1 0 1 0] [4]
[1 1 1 1] [2]
>>> from scipy.linalg import solve_triangular
>>> a = np.array([[3, 0, 0, 0], [2, 1, 0, 0], [1, 0, 1, 0], [1, 1, 1, 1]])
>>> b = np.array([4, 2, 4, 2])
>>> x = solve_triangular(a, b, lower=True)
>>> x
array([ 1.33333333, -0.66666667, 2.66666667, -1.33333333])
>>> a.dot(x) # Check the result
array([ 4., 2., 4., 2.])
"""
# Deprecate keyword "debug"
if debug is not None:
warnings.warn('Use of the "debug" keyword is deprecated '
'and this keyword will be removed in the future '
'versions of SciPy.', DeprecationWarning)
a1 = _asarray_validated(a, check_finite=check_finite)
b1 = _asarray_validated(b, check_finite=check_finite)
if len(a1.shape) != 2 or a1.shape[0] != a1.shape[1]:
raise ValueError('expected square matrix')
if a1.shape[0] != b1.shape[0]:
raise ValueError('incompatible dimensions')
overwrite_b = overwrite_b or _datacopied(b1, b)
if debug:
print('solve:overwrite_b=', overwrite_b)
trans = {'N': 0, 'T': 1, 'C': 2}.get(trans, trans)
trtrs, = get_lapack_funcs(('trtrs',), (a1, b1))
x, info = trtrs(a1, b1, overwrite_b=overwrite_b, lower=lower,
trans=trans, unitdiag=unit_diagonal)
if info == 0:
return x
if info > 0:
raise LinAlgError("singular matrix: resolution failed at diagonal %d" %
(info-1))
raise ValueError('illegal value in %d-th argument of internal trtrs' %
(-info))
def solve_banded(l_and_u, ab, b, overwrite_ab=False, overwrite_b=False,
debug=None, check_finite=True):
"""
Solve the equation a x = b for x, assuming a is banded matrix.
The matrix a is stored in `ab` using the matrix diagonal ordered form::
ab[u + i - j, j] == a[i,j]
Example of `ab` (shape of a is (6,6), `u` =1, `l` =2)::
* a01 a12 a23 a34 a45
a00 a11 a22 a33 a44 a55
a10 a21 a32 a43 a54 *
a20 a31 a42 a53 * *
Parameters
----------
(l, u) : (integer, integer)
Number of non-zero lower and upper diagonals
ab : (`l` + `u` + 1, M) array_like
Banded matrix
b : (M,) or (M, K) array_like
Right-hand side
overwrite_ab : bool, optional
Discard data in `ab` (may enhance performance)
overwrite_b : bool, optional
Discard data in `b` (may enhance performance)
check_finite : bool, optional
Whether to check that the input matrices contain only finite numbers.
Disabling may give a performance gain, but may result in problems
(crashes, non-termination) if the inputs do contain infinities or NaNs.
Returns
-------
x : (M,) or (M, K) ndarray
The solution to the system a x = b. Returned shape depends on the
shape of `b`.
Examples
--------
Solve the banded system a x = b, where::
[5 2 -1 0 0] [0]
[1 4 2 -1 0] [1]
a = [0 1 3 2 -1] b = [2]
[0 0 1 2 2] [2]
[0 0 0 1 1] [3]
There is one nonzero diagonal below the main diagonal (l = 1), and
two above (u = 2). The diagonal banded form of the matrix is::
[* * -1 -1 -1]
ab = [* 2 2 2 2]
[5 4 3 2 1]
[1 1 1 1 *]
>>> from scipy.linalg import solve_banded
>>> ab = np.array([[0, 0, -1, -1, -1],
... [0, 2, 2, 2, 2],
... [5, 4, 3, 2, 1],
... [1, 1, 1, 1, 0]])
>>> b = np.array([0, 1, 2, 2, 3])
>>> x = solve_banded((1, 2), ab, b)
>>> x
array([-2.37288136, 3.93220339, -4. , 4.3559322 , -1.3559322 ])
"""
# Deprecate keyword "debug"
if debug is not None:
warnings.warn('Use of the "debug" keyword is deprecated '
'and this keyword will be removed in the future '
'versions of SciPy.', DeprecationWarning)
a1 = _asarray_validated(ab, check_finite=check_finite, as_inexact=True)
b1 = _asarray_validated(b, check_finite=check_finite, as_inexact=True)
# Validate shapes.
if a1.shape[-1] != b1.shape[0]:
raise ValueError("shapes of ab and b are not compatible.")
(l, u) = l_and_u
if l + u + 1 != a1.shape[0]:
raise ValueError("invalid values for the number of lower and upper "
"diagonals: l+u+1 (%d) does not equal ab.shape[0] "
"(%d)" % (l+u+1, ab.shape[0]))
overwrite_b = overwrite_b or _datacopied(b1, b)
if a1.shape[-1] == 1:
b2 = np.array(b1, copy=(not overwrite_b))
b2 /= a1[1, 0]
return b2
if l == u == 1:
overwrite_ab = overwrite_ab or _datacopied(a1, ab)
gtsv, = get_lapack_funcs(('gtsv',), (a1, b1))
du = a1[0, 1:]
d = a1[1, :]
dl = a1[2, :-1]
du2, d, du, x, info = gtsv(dl, d, du, b1, overwrite_ab, overwrite_ab,
overwrite_ab, overwrite_b)
else:
gbsv, = get_lapack_funcs(('gbsv',), (a1, b1))
a2 = np.zeros((2*l+u+1, a1.shape[1]), dtype=gbsv.dtype)
a2[l:, :] = a1
lu, piv, x, info = gbsv(l, u, a2, b1, overwrite_ab=True,
overwrite_b=overwrite_b)
if info == 0:
return x
if info > 0:
raise LinAlgError("singular matrix")
raise ValueError('illegal value in %d-th argument of internal '
'gbsv/gtsv' % -info)
def solveh_banded(ab, b, overwrite_ab=False, overwrite_b=False, lower=False,
check_finite=True):
"""
Solve equation a x = b. a is Hermitian positive-definite banded matrix.
The matrix a is stored in `ab` either in lower diagonal or upper
diagonal ordered form:
ab[u + i - j, j] == a[i,j] (if upper form; i <= j)
ab[ i - j, j] == a[i,j] (if lower form; i >= j)
Example of `ab` (shape of a is (6, 6), `u` =2)::
upper form:
* * a02 a13 a24 a35
* a01 a12 a23 a34 a45
a00 a11 a22 a33 a44 a55
lower form:
a00 a11 a22 a33 a44 a55
a10 a21 a32 a43 a54 *
a20 a31 a42 a53 * *
Cells marked with * are not used.
Parameters
----------
ab : (`u` + 1, M) array_like
Banded matrix
b : (M,) or (M, K) array_like
Right-hand side
overwrite_ab : bool, optional
Discard data in `ab` (may enhance performance)
overwrite_b : bool, optional
Discard data in `b` (may enhance performance)
lower : bool, optional
Is the matrix in the lower form. (Default is upper form)
check_finite : bool, optional
Whether to check that the input matrices contain only finite numbers.
Disabling may give a performance gain, but may result in problems
(crashes, non-termination) if the inputs do contain infinities or NaNs.
Returns
-------
x : (M,) or (M, K) ndarray
The solution to the system a x = b. Shape of return matches shape
of `b`.
Examples
--------
Solve the banded system A x = b, where::
[ 4 2 -1 0 0 0] [1]
[ 2 5 2 -1 0 0] [2]
A = [-1 2 6 2 -1 0] b = [2]
[ 0 -1 2 7 2 -1] [3]
[ 0 0 -1 2 8 2] [3]
[ 0 0 0 -1 2 9] [3]
>>> from scipy.linalg import solveh_banded
`ab` contains the main diagonal and the nonzero diagonals below the
main diagonal. That is, we use the lower form:
>>> ab = np.array([[ 4, 5, 6, 7, 8, 9],
... [ 2, 2, 2, 2, 2, 0],
... [-1, -1, -1, -1, 0, 0]])
>>> b = np.array([1, 2, 2, 3, 3, 3])
>>> x = solveh_banded(ab, b, lower=True)
>>> x
array([ 0.03431373, 0.45938375, 0.05602241, 0.47759104, 0.17577031,
0.34733894])
Solve the Hermitian banded system H x = b, where::
[ 8 2-1j 0 0 ] [ 1 ]
H = [2+1j 5 1j 0 ] b = [1+1j]
[ 0 -1j 9 -2-1j] [1-2j]
[ 0 0 -2+1j 6 ] [ 0 ]
In this example, we put the upper diagonals in the array `hb`:
>>> hb = np.array([[0, 2-1j, 1j, -2-1j],
... [8, 5, 9, 6 ]])
>>> b = np.array([1, 1+1j, 1-2j, 0])
>>> x = solveh_banded(hb, b)
>>> x
array([ 0.07318536-0.02939412j, 0.11877624+0.17696461j,
0.10077984-0.23035393j, -0.00479904-0.09358128j])
"""
a1 = _asarray_validated(ab, check_finite=check_finite)
b1 = _asarray_validated(b, check_finite=check_finite)
# Validate shapes.
if a1.shape[-1] != b1.shape[0]:
raise ValueError("shapes of ab and b are not compatible.")
overwrite_b = overwrite_b or _datacopied(b1, b)
overwrite_ab = overwrite_ab or _datacopied(a1, ab)
if a1.shape[0] == 2:
ptsv, = get_lapack_funcs(('ptsv',), (a1, b1))
if lower:
d = a1[0, :].real
e = a1[1, :-1]
else:
d = a1[1, :].real
e = a1[0, 1:].conj()
d, du, x, info = ptsv(d, e, b1, overwrite_ab, overwrite_ab,
overwrite_b)
else:
pbsv, = get_lapack_funcs(('pbsv',), (a1, b1))
c, x, info = pbsv(a1, b1, lower=lower, overwrite_ab=overwrite_ab,
overwrite_b=overwrite_b)
if info > 0:
raise LinAlgError("%d-th leading minor not positive definite" % info)
if info < 0:
raise ValueError('illegal value in %d-th argument of internal '
'pbsv' % -info)
return x
def solve_toeplitz(c_or_cr, b, check_finite=True):
"""Solve a Toeplitz system using Levinson Recursion
The Toeplitz matrix has constant diagonals, with c as its first column
and r as its first row. If r is not given, ``r == conjugate(c)`` is
assumed.
Parameters
----------
c_or_cr : array_like or tuple of (array_like, array_like)
The vector ``c``, or a tuple of arrays (``c``, ``r``). Whatever the
actual shape of ``c``, it will be converted to a 1-D array. If not
supplied, ``r = conjugate(c)`` is assumed; in this case, if c[0] is
real, the Toeplitz matrix is Hermitian. r[0] is ignored; the first row
of the Toeplitz matrix is ``[c[0], r[1:]]``. Whatever the actual shape
of ``r``, it will be converted to a 1-D array.
b : (M,) or (M, K) array_like
Right-hand side in ``T x = b``.
check_finite : bool, optional
Whether to check that the input matrices contain only finite numbers.
Disabling may give a performance gain, but may result in problems
(result entirely NaNs) if the inputs do contain infinities or NaNs.
Returns
-------
x : (M,) or (M, K) ndarray
The solution to the system ``T x = b``. Shape of return matches shape
of `b`.
See Also
--------
toeplitz : Toeplitz matrix
Notes
-----
The solution is computed using Levinson-Durbin recursion, which is faster
than generic least-squares methods, but can be less numerically stable.
Examples
--------
Solve the Toeplitz system T x = b, where::
[ 1 -1 -2 -3] [1]
T = [ 3 1 -1 -2] b = [2]
[ 6 3 1 -1] [2]
[10 6 3 1] [5]
To specify the Toeplitz matrix, only the first column and the first
row are needed.
>>> c = np.array([1, 3, 6, 10]) # First column of T
>>> r = np.array([1, -1, -2, -3]) # First row of T
>>> b = np.array([1, 2, 2, 5])
>>> from scipy.linalg import solve_toeplitz, toeplitz
>>> x = solve_toeplitz((c, r), b)
>>> x
array([ 1.66666667, -1. , -2.66666667, 2.33333333])
Check the result by creating the full Toeplitz matrix and
multiplying it by `x`. We should get `b`.
>>> T = toeplitz(c, r)
>>> T.dot(x)
array([ 1., 2., 2., 5.])
"""
# If numerical stability of this algorithm is a problem, a future
# developer might consider implementing other O(N^2) Toeplitz solvers,
# such as GKO (http://www.jstor.org/stable/2153371) or Bareiss.
if isinstance(c_or_cr, tuple):
c, r = c_or_cr
c = _asarray_validated(c, check_finite=check_finite).ravel()
r = _asarray_validated(r, check_finite=check_finite).ravel()
else:
c = _asarray_validated(c_or_cr, check_finite=check_finite).ravel()
r = c.conjugate()
# Form a 1D array of values to be used in the matrix, containing a reversed
# copy of r[1:], followed by c.
vals = np.concatenate((r[-1:0:-1], c))
if b is None:
raise ValueError('illegal value, `b` is a required argument')
b = _asarray_validated(b)
if vals.shape[0] != (2*b.shape[0] - 1):
raise ValueError('incompatible dimensions')
if np.iscomplexobj(vals) or np.iscomplexobj(b):
vals = np.asarray(vals, dtype=np.complex128, order='c')
b = np.asarray(b, dtype=np.complex128)
else:
vals = np.asarray(vals, dtype=np.double, order='c')
b = np.asarray(b, dtype=np.double)
if b.ndim == 1:
x, _ = levinson(vals, np.ascontiguousarray(b))
else:
b_shape = b.shape
b = b.reshape(b.shape[0], -1)
x = np.column_stack(
(levinson(vals, np.ascontiguousarray(b[:, i]))[0])
for i in range(b.shape[1]))
x = x.reshape(*b_shape)
return x
def _get_axis_len(aname, a, axis):
ax = axis
if ax < 0:
ax += a.ndim
if 0 <= ax < a.ndim:
return a.shape[ax]
raise ValueError("'%saxis' entry is out of bounds" % (aname,))
def solve_circulant(c, b, singular='raise', tol=None,
caxis=-1, baxis=0, outaxis=0):
"""Solve C x = b for x, where C is a circulant matrix.
`C` is the circulant matrix associated with the vector `c`.
The system is solved by doing division in Fourier space. The
calculation is::
x = ifft(fft(b) / fft(c))
where `fft` and `ifft` are the fast Fourier transform and its inverse,
respectively. For a large vector `c`, this is *much* faster than
solving the system with the full circulant matrix.
Parameters
----------
c : array_like
The coefficients of the circulant matrix.
b : array_like
Right-hand side matrix in ``a x = b``.
singular : str, optional
This argument controls how a near singular circulant matrix is
handled. If `singular` is "raise" and the circulant matrix is
near singular, a `LinAlgError` is raised. If `singular` is
"lstsq", the least squares solution is returned. Default is "raise".
tol : float, optional
If any eigenvalue of the circulant matrix has an absolute value
that is less than or equal to `tol`, the matrix is considered to be
near singular. If not given, `tol` is set to::
tol = abs_eigs.max() * abs_eigs.size * np.finfo(np.float64).eps
where `abs_eigs` is the array of absolute values of the eigenvalues
of the circulant matrix.
caxis : int
When `c` has dimension greater than 1, it is viewed as a collection
of circulant vectors. In this case, `caxis` is the axis of `c` that
holds the vectors of circulant coefficients.
baxis : int
When `b` has dimension greater than 1, it is viewed as a collection
of vectors. In this case, `baxis` is the axis of `b` that holds the
right-hand side vectors.
outaxis : int
When `c` or `b` are multidimensional, the value returned by
`solve_circulant` is multidimensional. In this case, `outaxis` is
the axis of the result that holds the solution vectors.
Returns
-------
x : ndarray
Solution to the system ``C x = b``.
Raises
------
LinAlgError
If the circulant matrix associated with `c` is near singular.
See Also
--------
circulant : circulant matrix
Notes
-----
For a one-dimensional vector `c` with length `m`, and an array `b`
with shape ``(m, ...)``,
solve_circulant(c, b)
returns the same result as
solve(circulant(c), b)
where `solve` and `circulant` are from `scipy.linalg`.
.. versionadded:: 0.16.0
Examples
--------
>>> from scipy.linalg import solve_circulant, solve, circulant, lstsq
>>> c = np.array([2, 2, 4])
>>> b = np.array([1, 2, 3])
>>> solve_circulant(c, b)
array([ 0.75, -0.25, 0.25])
Compare that result to solving the system with `scipy.linalg.solve`:
>>> solve(circulant(c), b)
array([ 0.75, -0.25, 0.25])
A singular example:
>>> c = np.array([1, 1, 0, 0])
>>> b = np.array([1, 2, 3, 4])
Calling ``solve_circulant(c, b)`` will raise a `LinAlgError`. For the
least square solution, use the option ``singular='lstsq'``:
>>> solve_circulant(c, b, singular='lstsq')
array([ 0.25, 1.25, 2.25, 1.25])
Compare to `scipy.linalg.lstsq`:
>>> x, resid, rnk, s = lstsq(circulant(c), b)
>>> x
array([ 0.25, 1.25, 2.25, 1.25])
A broadcasting example:
Suppose we have the vectors of two circulant matrices stored in an array
with shape (2, 5), and three `b` vectors stored in an array with shape
(3, 5). For example,
>>> c = np.array([[1.5, 2, 3, 0, 0], [1, 1, 4, 3, 2]])
>>> b = np.arange(15).reshape(-1, 5)
We want to solve all combinations of circulant matrices and `b` vectors,
with the result stored in an array with shape (2, 3, 5). When we
disregard the axes of `c` and `b` that hold the vectors of coefficients,
the shapes of the collections are (2,) and (3,), respectively, which are
not compatible for broadcasting. To have a broadcast result with shape
(2, 3), we add a trivial dimension to `c`: ``c[:, np.newaxis, :]`` has
shape (2, 1, 5). The last dimension holds the coefficients of the
circulant matrices, so when we call `solve_circulant`, we can use the
default ``caxis=-1``. The coefficients of the `b` vectors are in the last
dimension of the array `b`, so we use ``baxis=-1``. If we use the
default `outaxis`, the result will have shape (5, 2, 3), so we'll use
``outaxis=-1`` to put the solution vectors in the last dimension.
>>> x = solve_circulant(c[:, np.newaxis, :], b, baxis=-1, outaxis=-1)
>>> x.shape
(2, 3, 5)
>>> np.set_printoptions(precision=3) # For compact output of numbers.
>>> x
array([[[-0.118, 0.22 , 1.277, -0.142, 0.302],
[ 0.651, 0.989, 2.046, 0.627, 1.072],
[ 1.42 , 1.758, 2.816, 1.396, 1.841]],
[[ 0.401, 0.304, 0.694, -0.867, 0.377],
[ 0.856, 0.758, 1.149, -0.412, 0.831],
[ 1.31 , 1.213, 1.603, 0.042, 1.286]]])
Check by solving one pair of `c` and `b` vectors (cf. ``x[1, 1, :]``):
>>> solve_circulant(c[1], b[1, :])
array([ 0.856, 0.758, 1.149, -0.412, 0.831])
"""
c = np.atleast_1d(c)
nc = _get_axis_len("c", c, caxis)
b = np.atleast_1d(b)
nb = _get_axis_len("b", b, baxis)
if nc != nb:
raise ValueError('Incompatible c and b axis lengths')
fc = np.fft.fft(np.rollaxis(c, caxis, c.ndim), axis=-1)
abs_fc = np.abs(fc)
if tol is None:
# This is the same tolerance as used in np.linalg.matrix_rank.
tol = abs_fc.max(axis=-1) * nc * np.finfo(np.float64).eps
if tol.shape != ():
tol.shape = tol.shape + (1,)
else:
tol = np.atleast_1d(tol)
near_zeros = abs_fc <= tol
is_near_singular = np.any(near_zeros)
if is_near_singular:
if singular == 'raise':
raise LinAlgError("near singular circulant matrix.")
else:
# Replace the small values with 1 to avoid errors in the
# division fb/fc below.
fc[near_zeros] = 1
fb = np.fft.fft(np.rollaxis(b, baxis, b.ndim), axis=-1)
q = fb / fc
if is_near_singular:
# `near_zeros` is a boolean array, same shape as `c`, that is
# True where `fc` is (near) zero. `q` is the broadcasted result
# of fb / fc, so to set the values of `q` to 0 where `fc` is near
# zero, we use a mask that is the broadcast result of an array
# of True values shaped like `b` with `near_zeros`.
mask = np.ones_like(b, dtype=bool) & near_zeros
q[mask] = 0
x = np.fft.ifft(q, axis=-1)
if not (np.iscomplexobj(c) or np.iscomplexobj(b)):
x = x.real
if outaxis != -1:
x = np.rollaxis(x, -1, outaxis)
return x
# matrix inversion
def inv(a, overwrite_a=False, check_finite=True):
"""
Compute the inverse of a matrix.
Parameters
----------
a : array_like
Square matrix to be inverted.
overwrite_a : bool, optional
Discard data in `a` (may improve performance). Default is False.
check_finite : bool, optional
Whether to check that the input matrix contains only finite numbers.
Disabling may give a performance gain, but may result in problems
(crashes, non-termination) if the inputs do contain infinities or NaNs.
Returns
-------
ainv : ndarray
Inverse of the matrix `a`.
Raises
------
LinAlgError
If `a` is singular.
ValueError
If `a` is not square, or not 2-dimensional.
Examples
--------
>>> from scipy import linalg
>>> a = np.array([[1., 2.], [3., 4.]])
>>> linalg.inv(a)
array([[-2. , 1. ],
[ 1.5, -0.5]])
>>> np.dot(a, linalg.inv(a))
array([[ 1., 0.],
[ 0., 1.]])
"""
a1 = _asarray_validated(a, check_finite=check_finite)
if len(a1.shape) != 2 or a1.shape[0] != a1.shape[1]:
raise ValueError('expected square matrix')
overwrite_a = overwrite_a or _datacopied(a1, a)
#XXX: I found no advantage or disadvantage of using finv.
# finv, = get_flinalg_funcs(('inv',),(a1,))
# if finv is not None:
# a_inv,info = finv(a1,overwrite_a=overwrite_a)
# if info==0:
# return a_inv
# if info>0: raise LinAlgError, "singular matrix"
# if info<0: raise ValueError('illegal value in %d-th argument of '
# 'internal inv.getrf|getri'%(-info))
getrf, getri, getri_lwork = get_lapack_funcs(('getrf', 'getri',
'getri_lwork'),
(a1,))
lu, piv, info = getrf(a1, overwrite_a=overwrite_a)
if info == 0:
lwork = _compute_lwork(getri_lwork, a1.shape[0])
# XXX: the following line fixes curious SEGFAULT when
# benchmarking 500x500 matrix inverse. This seems to
# be a bug in LAPACK ?getri routine because if lwork is
# minimal (when using lwork[0] instead of lwork[1]) then
# all tests pass. Further investigation is required if
# more such SEGFAULTs occur.
lwork = int(1.01 * lwork)
inv_a, info = getri(lu, piv, lwork=lwork, overwrite_lu=1)
if info > 0:
raise LinAlgError("singular matrix")
if info < 0:
raise ValueError('illegal value in %d-th argument of internal '
'getrf|getri' % -info)
return inv_a
# Determinant
def det(a, overwrite_a=False, check_finite=True):
"""
Compute the determinant of a matrix
The determinant of a square matrix is a value derived arithmetically
from the coefficients of the matrix.
The determinant for a 3x3 matrix, for example, is computed as follows::
a b c
d e f = A
g h i
det(A) = a*e*i + b*f*g + c*d*h - c*e*g - b*d*i - a*f*h
Parameters
----------
a : (M, M) array_like
A square matrix.
overwrite_a : bool, optional
Allow overwriting data in a (may enhance performance).
check_finite : bool, optional
Whether to check that the input matrix contains only finite numbers.
Disabling may give a performance gain, but may result in problems
(crashes, non-termination) if the inputs do contain infinities or NaNs.
Returns
-------
det : float or complex
Determinant of `a`.
Notes
-----
The determinant is computed via LU factorization, LAPACK routine z/dgetrf.
Examples
--------
>>> from scipy import linalg
>>> a = np.array([[1,2,3], [4,5,6], [7,8,9]])
>>> linalg.det(a)
0.0
>>> a = np.array([[0,2,3], [4,5,6], [7,8,9]])
>>> linalg.det(a)
3.0
"""
a1 = _asarray_validated(a, check_finite=check_finite)
if len(a1.shape) != 2 or a1.shape[0] != a1.shape[1]:
raise ValueError('expected square matrix')
overwrite_a = overwrite_a or _datacopied(a1, a)
fdet, = get_flinalg_funcs(('det',), (a1,))
a_det, info = fdet(a1, overwrite_a=overwrite_a)
if info < 0:
raise ValueError('illegal value in %d-th argument of internal '
'det.getrf' % -info)
return a_det
# Linear Least Squares
class LstsqLapackError(LinAlgError):
pass
def lstsq(a, b, cond=None, overwrite_a=False, overwrite_b=False,
check_finite=True, lapack_driver=None):
"""
Compute least-squares solution to equation Ax = b.
Compute a vector x such that the 2-norm ``|b - A x|`` is minimized.
Parameters
----------
a : (M, N) array_like
Left hand side matrix (2-D array).
b : (M,) or (M, K) array_like
Right hand side matrix or vector (1-D or 2-D array).
cond : float, optional
Cutoff for 'small' singular values; used to determine effective
rank of a. Singular values smaller than
``rcond * largest_singular_value`` are considered zero.
overwrite_a : bool, optional
Discard data in `a` (may enhance performance). Default is False.
overwrite_b : bool, optional
Discard data in `b` (may enhance performance). Default is False.
check_finite : bool, optional
Whether to check that the input matrices contain only finite numbers.
Disabling may give a performance gain, but may result in problems
(crashes, non-termination) if the inputs do contain infinities or NaNs.
lapack_driver : str, optional
Which LAPACK driver is used to solve the least-squares problem.
Options are ``'gelsd'``, ``'gelsy'``, ``'gelss'``. Default
(``'gelsd'``) is a good choice. However, ``'gelsy'`` can be slightly
faster on many problems. ``'gelss'`` was used historically. It is
generally slow but uses less memory.
.. versionadded:: 0.17.0
Returns
-------
x : (N,) or (N, K) ndarray
Least-squares solution. Return shape matches shape of `b`.
residues : (0,) or () or (K,) ndarray
Sums of residues, squared 2-norm for each column in ``b - a x``.
If rank of matrix a is ``< N`` or ``N > M``, or ``'gelsy'`` is used,
this is a lenght zero array. If b was 1-D, this is a () shape array
(numpy scalar), otherwise the shape is (K,).
rank : int
Effective rank of matrix `a`.
s : (min(M,N),) ndarray or None
Singular values of `a`. The condition number of a is
``abs(s[0] / s[-1])``. None is returned when ``'gelsy'`` is used.
Raises
------
LinAlgError
If computation does not converge.
ValueError
When parameters are wrong.
See Also
--------
optimize.nnls : linear least squares with non-negativity constraint
Examples
--------
>>> from scipy.linalg import lstsq
>>> import matplotlib.pyplot as plt
Suppose we have the following data:
>>> x = np.array([1, 2.5, 3.5, 4, 5, 7, 8.5])
>>> y = np.array([0.3, 1.1, 1.5, 2.0, 3.2, 6.6, 8.6])
We want to fit a quadratic polynomial of the form ``y = a + b*x**2``
to this data. We first form the "design matrix" M, with a constant
column of 1s and a column containing ``x**2``:
>>> M = x[:, np.newaxis]**[0, 2]
>>> M
array([[ 1. , 1. ],
[ 1. , 6.25],
[ 1. , 12.25],
[ 1. , 16. ],
[ 1. , 25. ],
[ 1. , 49. ],
[ 1. , 72.25]])
We want to find the least-squares solution to ``M.dot(p) = y``,
where ``p`` is a vector with length 2 that holds the parameters
``a`` and ``b``.
>>> p, res, rnk, s = lstsq(M, y)
>>> p
array([ 0.20925829, 0.12013861])
Plot the data and the fitted curve.
>>> plt.plot(x, y, 'o', label='data')
>>> xx = np.linspace(0, 9, 101)
>>> yy = p[0] + p[1]*xx**2
>>> plt.plot(xx, yy, label='least squares fit, $y = a + bx^2$')
>>> plt.xlabel('x')
>>> plt.ylabel('y')
>>> plt.legend(framealpha=1, shadow=True)
>>> plt.grid(alpha=0.25)
>>> plt.show()
"""
a1 = _asarray_validated(a, check_finite=check_finite)
b1 = _asarray_validated(b, check_finite=check_finite)
if len(a1.shape) != 2:
raise ValueError('expected matrix')
m, n = a1.shape
if len(b1.shape) == 2:
nrhs = b1.shape[1]
else:
nrhs = 1
if m != b1.shape[0]:
raise ValueError('incompatible dimensions')
if m == 0 or n == 0: # Zero-sized problem, confuses LAPACK
x = np.zeros((n,) + b1.shape[1:], dtype=np.common_type(a1, b1))
if n == 0:
residues = np.linalg.norm(b1, axis=0)**2
else:
residues = np.empty((0,))
return x, residues, 0, np.empty((0,))
driver = lapack_driver
if driver is None:
driver = lstsq.default_lapack_driver
if driver not in ('gelsd', 'gelsy', 'gelss'):
raise ValueError('LAPACK driver "%s" is not found' % driver)
lapack_func, lapack_lwork = get_lapack_funcs((driver,
'%s_lwork' % driver),
(a1, b1))
real_data = True if (lapack_func.dtype.kind == 'f') else False
if m < n:
# need to extend b matrix as it will be filled with
# a larger solution matrix
if len(b1.shape) == 2:
b2 = np.zeros((n, nrhs), dtype=lapack_func.dtype)
b2[:m, :] = b1
else:
b2 = np.zeros(n, dtype=lapack_func.dtype)
b2[:m] = b1
b1 = b2
overwrite_a = overwrite_a or _datacopied(a1, a)
overwrite_b = overwrite_b or _datacopied(b1, b)
if cond is None:
cond = np.finfo(lapack_func.dtype).eps
if driver in ('gelss', 'gelsd'):
if driver == 'gelss':
lwork = _compute_lwork(lapack_lwork, m, n, nrhs, cond)
v, x, s, rank, work, info = lapack_func(a1, b1, cond, lwork,
overwrite_a=overwrite_a,
overwrite_b=overwrite_b)
elif driver == 'gelsd':
if real_data:
lwork, iwork = _compute_lwork(lapack_lwork, m, n, nrhs, cond)
if iwork == 0:
# this is LAPACK bug 0038: dgelsd does not provide the
# size of the iwork array in query mode. This bug was
# fixed in LAPACK 3.2.2, released July 21, 2010.
mesg = ("internal gelsd driver lwork query error, "
"required iwork dimension not returned. "
"This is likely the result of LAPACK bug "
"0038, fixed in LAPACK 3.2.2 (released "
"July 21, 2010). ")
if lapack_driver is None:
# restart with gelss
lstsq.default_lapack_driver = 'gelss'
mesg += "Falling back to 'gelss' driver."
warnings.warn(mesg, RuntimeWarning)
return lstsq(a, b, cond, overwrite_a, overwrite_b,
check_finite, lapack_driver='gelss')
# can't proceed, bail out
mesg += ("Use a different lapack_driver when calling lstsq"
" or upgrade LAPACK.")
raise LstsqLapackError(mesg)
x, s, rank, info = lapack_func(a1, b1, lwork,
iwork, cond, False, False)
else: # complex data
lwork, rwork, iwork = _compute_lwork(lapack_lwork, m, n,
nrhs, cond)
x, s, rank, info = lapack_func(a1, b1, lwork, rwork, iwork,
cond, False, False)
if info > 0:
raise LinAlgError("SVD did not converge in Linear Least Squares")
if info < 0:
raise ValueError('illegal value in %d-th argument of internal %s'
% (-info, lapack_driver))
resids = np.asarray([], dtype=x.dtype)
if m > n:
x1 = x[:n]
if rank == n:
resids = np.sum(np.abs(x[n:])**2, axis=0)
x = x1
return x, resids, rank, s
elif driver == 'gelsy':
lwork = _compute_lwork(lapack_lwork, m, n, nrhs, cond)
jptv = np.zeros((a1.shape[1], 1), dtype=np.int32)
v, x, j, rank, info = lapack_func(a1, b1, jptv, cond,
lwork, False, False)
if info < 0:
raise ValueError("illegal value in %d-th argument of internal "
"gelsy" % -info)
if m > n:
x1 = x[:n]
x = x1
return x, np.array([], x.dtype), rank, None
lstsq.default_lapack_driver = 'gelsd'
def pinv(a, cond=None, rcond=None, return_rank=False, check_finite=True):
"""
Compute the (Moore-Penrose) pseudo-inverse of a matrix.
Calculate a generalized inverse of a matrix using a least-squares
solver.
Parameters
----------
a : (M, N) array_like
Matrix to be pseudo-inverted.
cond, rcond : float, optional
Cutoff for 'small' singular values in the least-squares solver.
Singular values smaller than ``rcond * largest_singular_value``
are considered zero.
return_rank : bool, optional
if True, return the effective rank of the matrix
check_finite : bool, optional
Whether to check that the input matrix contains only finite numbers.
Disabling may give a performance gain, but may result in problems
(crashes, non-termination) if the inputs do contain infinities or NaNs.
Returns
-------
B : (N, M) ndarray
The pseudo-inverse of matrix `a`.
rank : int
The effective rank of the matrix. Returned if return_rank == True
Raises
------
LinAlgError
If computation does not converge.
Examples
--------
>>> from scipy import linalg
>>> a = np.random.randn(9, 6)
>>> B = linalg.pinv(a)
>>> np.allclose(a, np.dot(a, np.dot(B, a)))
True
>>> np.allclose(B, np.dot(B, np.dot(a, B)))
True
"""
a = _asarray_validated(a, check_finite=check_finite)
b = np.identity(a.shape[0], dtype=a.dtype)
if rcond is not None:
cond = rcond
x, resids, rank, s = lstsq(a, b, cond=cond, check_finite=False)
if return_rank:
return x, rank
else:
return x
def pinv2(a, cond=None, rcond=None, return_rank=False, check_finite=True):
"""
Compute the (Moore-Penrose) pseudo-inverse of a matrix.
Calculate a generalized inverse of a matrix using its
singular-value decomposition and including all 'large' singular
values.
Parameters
----------
a : (M, N) array_like
Matrix to be pseudo-inverted.
cond, rcond : float or None
Cutoff for 'small' singular values.
Singular values smaller than ``rcond*largest_singular_value``
are considered zero.
If None or -1, suitable machine precision is used.
return_rank : bool, optional
if True, return the effective rank of the matrix
check_finite : bool, optional
Whether to check that the input matrix contains only finite numbers.
Disabling may give a performance gain, but may result in problems
(crashes, non-termination) if the inputs do contain infinities or NaNs.
Returns
-------
B : (N, M) ndarray
The pseudo-inverse of matrix `a`.
rank : int
The effective rank of the matrix. Returned if return_rank == True
Raises
------
LinAlgError
If SVD computation does not converge.
Examples
--------
>>> from scipy import linalg
>>> a = np.random.randn(9, 6)
>>> B = linalg.pinv2(a)
>>> np.allclose(a, np.dot(a, np.dot(B, a)))
True
>>> np.allclose(B, np.dot(B, np.dot(a, B)))
True
"""
a = _asarray_validated(a, check_finite=check_finite)
u, s, vh = decomp_svd.svd(a, full_matrices=False, check_finite=False)
if rcond is not None:
cond = rcond
if cond in [None, -1]:
t = u.dtype.char.lower()
factor = {'f': 1E3, 'd': 1E6}
cond = factor[t] * np.finfo(t).eps
rank = np.sum(s > cond * np.max(s))
u = u[:, :rank]
u /= s[:rank]
B = np.transpose(np.conjugate(np.dot(u, vh[:rank])))
if return_rank:
return B, rank
else:
return B
def pinvh(a, cond=None, rcond=None, lower=True, return_rank=False,
check_finite=True):
"""
Compute the (Moore-Penrose) pseudo-inverse of a Hermitian matrix.
Calculate a generalized inverse of a Hermitian or real symmetric matrix
using its eigenvalue decomposition and including all eigenvalues with
'large' absolute value.
Parameters
----------
a : (N, N) array_like
Real symmetric or complex hermetian matrix to be pseudo-inverted
cond, rcond : float or None
Cutoff for 'small' eigenvalues.
Singular values smaller than rcond * largest_eigenvalue are considered
zero.
If None or -1, suitable machine precision is used.
lower : bool, optional
Whether the pertinent array data is taken from the lower or upper
triangle of a. (Default: lower)
return_rank : bool, optional
if True, return the effective rank of the matrix
check_finite : bool, optional
Whether to check that the input matrix contains only finite numbers.
Disabling may give a performance gain, but may result in problems
(crashes, non-termination) if the inputs do contain infinities or NaNs.
Returns
-------
B : (N, N) ndarray
The pseudo-inverse of matrix `a`.
rank : int
The effective rank of the matrix. Returned if return_rank == True
Raises
------
LinAlgError
If eigenvalue does not converge
Examples
--------
>>> from scipy.linalg import pinvh
>>> a = np.random.randn(9, 6)
>>> a = np.dot(a, a.T)
>>> B = pinvh(a)
>>> np.allclose(a, np.dot(a, np.dot(B, a)))
True
>>> np.allclose(B, np.dot(B, np.dot(a, B)))
True
"""
a = _asarray_validated(a, check_finite=check_finite)
s, u = decomp.eigh(a, lower=lower, check_finite=False)
if rcond is not None:
cond = rcond
if cond in [None, -1]:
t = u.dtype.char.lower()
factor = {'f': 1E3, 'd': 1E6}
cond = factor[t] * np.finfo(t).eps
# For Hermitian matrices, singular values equal abs(eigenvalues)
above_cutoff = (abs(s) > cond * np.max(abs(s)))
psigma_diag = 1.0 / s[above_cutoff]
u = u[:, above_cutoff]
B = np.dot(u * psigma_diag, np.conjugate(u).T)
if return_rank:
return B, len(psigma_diag)
else:
return B
def matrix_balance(A, permute=True, scale=True, separate=False,
overwrite_a=False):
"""
Compute a diagonal similarity transformation for row/column balancing.
The balancing tries to equalize the row and column 1-norms by applying
a similarity transformation such that the magnitude variation of the
matrix entries is reflected to the scaling matrices.
Moreover, if enabled, the matrix is first permuted to isolate the upper
triangular parts of the matrix and, again if scaling is also enabled,
only the remaining subblocks are subjected to scaling.
The balanced matrix satisfies the following equality
.. math::
B = T^{-1} A T
The scaling coefficients are approximated to the nearest power of 2
to avoid round-off errors.
Parameters
----------
A : (n, n) array_like
Square data matrix for the balancing.
permute : bool, optional
The selector to define whether permutation of A is also performed
prior to scaling.
scale : bool, optional
The selector to turn on and off the scaling. If False, the matrix
will not be scaled.
separate : bool, optional
This switches from returning a full matrix of the transformation
to a tuple of two separate 1D permutation and scaling arrays.
overwrite_a : bool, optional
This is passed to xGEBAL directly. Essentially, overwrites the result
to the data. It might increase the space efficiency. See LAPACK manual
for details. This is False by default.
Returns
-------
B : (n, n) ndarray
Balanced matrix
T : (n, n) ndarray
A possibly permuted diagonal matrix whose nonzero entries are
integer powers of 2 to avoid numerical truncation errors.
scale, perm : (n,) ndarray
If ``separate`` keyword is set to True then instead of the array
``T`` above, the scaling and the permutation vectors are given
separately as a tuple without allocating the full array ``T``.
.. versionadded:: 0.19.0
Notes
-----
This algorithm is particularly useful for eigenvalue and matrix
decompositions and in many cases it is already called by various
LAPACK routines.
The algorithm is based on the well-known technique of [1]_ and has
been modified to account for special cases. See [2]_ for details
which have been implemented since LAPACK v3.5.0. Before this version
there are corner cases where balancing can actually worsen the
conditioning. See [3]_ for such examples.
The code is a wrapper around LAPACK's xGEBAL routine family for matrix
balancing.
Examples
--------
>>> from scipy import linalg
>>> x = np.array([[1,2,0], [9,1,0.01], [1,2,10*np.pi]])
>>> y, permscale = linalg.matrix_balance(x)
>>> np.abs(x).sum(axis=0) / np.abs(x).sum(axis=1)
array([ 3.66666667, 0.4995005 , 0.91312162])
>>> np.abs(y).sum(axis=0) / np.abs(y).sum(axis=1)
array([ 1.2 , 1.27041742, 0.92658316]) # may vary
>>> permscale # only powers of 2 (0.5 == 2^(-1))
array([[ 0.5, 0. , 0. ], # may vary
[ 0. , 1. , 0. ],
[ 0. , 0. , 1. ]])
References
----------
.. [1] : B.N. Parlett and C. Reinsch, "Balancing a Matrix for
Calculation of Eigenvalues and Eigenvectors", Numerische Mathematik,
Vol.13(4), 1969, DOI:10.1007/BF02165404
.. [2] : R. James, J. Langou, B.R. Lowery, "On matrix balancing and
eigenvector computation", 2014, Available online:
http://arxiv.org/abs/1401.5766
.. [3] : D.S. Watkins. A case where balancing is harmful.
Electron. Trans. Numer. Anal, Vol.23, 2006.
"""
A = np.atleast_2d(_asarray_validated(A, check_finite=True))
if not np.equal(*A.shape):
raise ValueError('The data matrix for balancing should be square.')
gebal = get_lapack_funcs(('gebal'), (A,))
B, lo, hi, ps, info = gebal(A, scale=scale, permute=permute,
overwrite_a=overwrite_a)
if info < 0:
raise ValueError('xGEBAL exited with the internal error '
'"illegal value in argument number {}.". See '
'LAPACK documentation for the xGEBAL error codes.'
''.format(-info))
# Separate the permutations from the scalings and then convert to int
scaling = np.ones_like(ps, dtype=float)
scaling[lo:hi+1] = ps[lo:hi+1]
# gebal uses 1-indexing
ps = ps.astype(int, copy=False) - 1
n = A.shape[0]
perm = np.arange(n)
# LAPACK permutes with the ordering n --> hi, then 0--> lo
if hi < n:
for ind, x in enumerate(ps[hi+1:][::-1], 1):
if n-ind == x:
continue
perm[[x, n-ind]] = perm[[n-ind, x]]
if lo > 0:
for ind, x in enumerate(ps[:lo]):
if ind == x:
continue
perm[[x, ind]] = perm[[ind, x]]
if separate:
return B, (scaling, perm)
# get the inverse permutation
iperm = np.empty_like(perm)
iperm[perm] = np.arange(n)
return B, np.diag(scaling)[iperm, :]