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Traktor/myenv/Lib/site-packages/sympy/matrices/decompositions.py

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2024-05-23 01:57:24 +02:00
import copy
from sympy.core import S
from sympy.core.function import expand_mul
from sympy.functions.elementary.miscellaneous import Min, sqrt
from sympy.functions.elementary.complexes import sign
from .common import NonSquareMatrixError, NonPositiveDefiniteMatrixError
from .utilities import _get_intermediate_simp, _iszero
from .determinant import _find_reasonable_pivot_naive
def _rank_decomposition(M, iszerofunc=_iszero, simplify=False):
r"""Returns a pair of matrices (`C`, `F`) with matching rank
such that `A = C F`.
Parameters
==========
iszerofunc : Function, optional
A function used for detecting whether an element can
act as a pivot. ``lambda x: x.is_zero`` is used by default.
simplify : Bool or Function, optional
A function used to simplify elements when looking for a
pivot. By default SymPy's ``simplify`` is used.
Returns
=======
(C, F) : Matrices
`C` and `F` are full-rank matrices with rank as same as `A`,
whose product gives `A`.
See Notes for additional mathematical details.
Examples
========
>>> from sympy import Matrix
>>> A = Matrix([
... [1, 3, 1, 4],
... [2, 7, 3, 9],
... [1, 5, 3, 1],
... [1, 2, 0, 8]
... ])
>>> C, F = A.rank_decomposition()
>>> C
Matrix([
[1, 3, 4],
[2, 7, 9],
[1, 5, 1],
[1, 2, 8]])
>>> F
Matrix([
[1, 0, -2, 0],
[0, 1, 1, 0],
[0, 0, 0, 1]])
>>> C * F == A
True
Notes
=====
Obtaining `F`, an RREF of `A`, is equivalent to creating a
product
.. math::
E_n E_{n-1} ... E_1 A = F
where `E_n, E_{n-1}, \dots, E_1` are the elimination matrices or
permutation matrices equivalent to each row-reduction step.
The inverse of the same product of elimination matrices gives
`C`:
.. math::
C = \left(E_n E_{n-1} \dots E_1\right)^{-1}
It is not necessary, however, to actually compute the inverse:
the columns of `C` are those from the original matrix with the
same column indices as the indices of the pivot columns of `F`.
References
==========
.. [1] https://en.wikipedia.org/wiki/Rank_factorization
.. [2] Piziak, R.; Odell, P. L. (1 June 1999).
"Full Rank Factorization of Matrices".
Mathematics Magazine. 72 (3): 193. doi:10.2307/2690882
See Also
========
sympy.matrices.matrices.MatrixReductions.rref
"""
F, pivot_cols = M.rref(simplify=simplify, iszerofunc=iszerofunc,
pivots=True)
rank = len(pivot_cols)
C = M.extract(range(M.rows), pivot_cols)
F = F[:rank, :]
return C, F
def _liupc(M):
"""Liu's algorithm, for pre-determination of the Elimination Tree of
the given matrix, used in row-based symbolic Cholesky factorization.
Examples
========
>>> from sympy import SparseMatrix
>>> S = SparseMatrix([
... [1, 0, 3, 2],
... [0, 0, 1, 0],
... [4, 0, 0, 5],
... [0, 6, 7, 0]])
>>> S.liupc()
([[0], [], [0], [1, 2]], [4, 3, 4, 4])
References
==========
.. [1] Symbolic Sparse Cholesky Factorization using Elimination Trees,
Jeroen Van Grondelle (1999)
https://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.39.7582
"""
# Algorithm 2.4, p 17 of reference
# get the indices of the elements that are non-zero on or below diag
R = [[] for r in range(M.rows)]
for r, c, _ in M.row_list():
if c <= r:
R[r].append(c)
inf = len(R) # nothing will be this large
parent = [inf]*M.rows
virtual = [inf]*M.rows
for r in range(M.rows):
for c in R[r][:-1]:
while virtual[c] < r:
t = virtual[c]
virtual[c] = r
c = t
if virtual[c] == inf:
parent[c] = virtual[c] = r
return R, parent
def _row_structure_symbolic_cholesky(M):
"""Symbolic cholesky factorization, for pre-determination of the
non-zero structure of the Cholesky factororization.
Examples
========
>>> from sympy import SparseMatrix
>>> S = SparseMatrix([
... [1, 0, 3, 2],
... [0, 0, 1, 0],
... [4, 0, 0, 5],
... [0, 6, 7, 0]])
>>> S.row_structure_symbolic_cholesky()
[[0], [], [0], [1, 2]]
References
==========
.. [1] Symbolic Sparse Cholesky Factorization using Elimination Trees,
Jeroen Van Grondelle (1999)
https://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.39.7582
"""
R, parent = M.liupc()
inf = len(R) # this acts as infinity
Lrow = copy.deepcopy(R)
for k in range(M.rows):
for j in R[k]:
while j != inf and j != k:
Lrow[k].append(j)
j = parent[j]
Lrow[k] = sorted(set(Lrow[k]))
return Lrow
def _cholesky(M, hermitian=True):
"""Returns the Cholesky-type decomposition L of a matrix A
such that L * L.H == A if hermitian flag is True,
or L * L.T == A if hermitian is False.
A must be a Hermitian positive-definite matrix if hermitian is True,
or a symmetric matrix if it is False.
Examples
========
>>> from sympy import Matrix
>>> A = Matrix(((25, 15, -5), (15, 18, 0), (-5, 0, 11)))
>>> A.cholesky()
Matrix([
[ 5, 0, 0],
[ 3, 3, 0],
[-1, 1, 3]])
>>> A.cholesky() * A.cholesky().T
Matrix([
[25, 15, -5],
[15, 18, 0],
[-5, 0, 11]])
The matrix can have complex entries:
>>> from sympy import I
>>> A = Matrix(((9, 3*I), (-3*I, 5)))
>>> A.cholesky()
Matrix([
[ 3, 0],
[-I, 2]])
>>> A.cholesky() * A.cholesky().H
Matrix([
[ 9, 3*I],
[-3*I, 5]])
Non-hermitian Cholesky-type decomposition may be useful when the
matrix is not positive-definite.
>>> A = Matrix([[1, 2], [2, 1]])
>>> L = A.cholesky(hermitian=False)
>>> L
Matrix([
[1, 0],
[2, sqrt(3)*I]])
>>> L*L.T == A
True
See Also
========
sympy.matrices.dense.DenseMatrix.LDLdecomposition
sympy.matrices.matrices.MatrixBase.LUdecomposition
QRdecomposition
"""
from .dense import MutableDenseMatrix
if not M.is_square:
raise NonSquareMatrixError("Matrix must be square.")
if hermitian and not M.is_hermitian:
raise ValueError("Matrix must be Hermitian.")
if not hermitian and not M.is_symmetric():
raise ValueError("Matrix must be symmetric.")
L = MutableDenseMatrix.zeros(M.rows, M.rows)
if hermitian:
for i in range(M.rows):
for j in range(i):
L[i, j] = ((1 / L[j, j])*(M[i, j] -
sum(L[i, k]*L[j, k].conjugate() for k in range(j))))
Lii2 = (M[i, i] -
sum(L[i, k]*L[i, k].conjugate() for k in range(i)))
if Lii2.is_positive is False:
raise NonPositiveDefiniteMatrixError(
"Matrix must be positive-definite")
L[i, i] = sqrt(Lii2)
else:
for i in range(M.rows):
for j in range(i):
L[i, j] = ((1 / L[j, j])*(M[i, j] -
sum(L[i, k]*L[j, k] for k in range(j))))
L[i, i] = sqrt(M[i, i] -
sum(L[i, k]**2 for k in range(i)))
return M._new(L)
def _cholesky_sparse(M, hermitian=True):
"""
Returns the Cholesky decomposition L of a matrix A
such that L * L.T = A
A must be a square, symmetric, positive-definite
and non-singular matrix
Examples
========
>>> from sympy import SparseMatrix
>>> A = SparseMatrix(((25,15,-5),(15,18,0),(-5,0,11)))
>>> A.cholesky()
Matrix([
[ 5, 0, 0],
[ 3, 3, 0],
[-1, 1, 3]])
>>> A.cholesky() * A.cholesky().T == A
True
The matrix can have complex entries:
>>> from sympy import I
>>> A = SparseMatrix(((9, 3*I), (-3*I, 5)))
>>> A.cholesky()
Matrix([
[ 3, 0],
[-I, 2]])
>>> A.cholesky() * A.cholesky().H
Matrix([
[ 9, 3*I],
[-3*I, 5]])
Non-hermitian Cholesky-type decomposition may be useful when the
matrix is not positive-definite.
>>> A = SparseMatrix([[1, 2], [2, 1]])
>>> L = A.cholesky(hermitian=False)
>>> L
Matrix([
[1, 0],
[2, sqrt(3)*I]])
>>> L*L.T == A
True
See Also
========
sympy.matrices.sparse.SparseMatrix.LDLdecomposition
sympy.matrices.matrices.MatrixBase.LUdecomposition
QRdecomposition
"""
from .dense import MutableDenseMatrix
if not M.is_square:
raise NonSquareMatrixError("Matrix must be square.")
if hermitian and not M.is_hermitian:
raise ValueError("Matrix must be Hermitian.")
if not hermitian and not M.is_symmetric():
raise ValueError("Matrix must be symmetric.")
dps = _get_intermediate_simp(expand_mul, expand_mul)
Crowstruc = M.row_structure_symbolic_cholesky()
C = MutableDenseMatrix.zeros(M.rows)
for i in range(len(Crowstruc)):
for j in Crowstruc[i]:
if i != j:
C[i, j] = M[i, j]
summ = 0
for p1 in Crowstruc[i]:
if p1 < j:
for p2 in Crowstruc[j]:
if p2 < j:
if p1 == p2:
if hermitian:
summ += C[i, p1]*C[j, p1].conjugate()
else:
summ += C[i, p1]*C[j, p1]
else:
break
else:
break
C[i, j] = dps((C[i, j] - summ) / C[j, j])
else: # i == j
C[j, j] = M[j, j]
summ = 0
for k in Crowstruc[j]:
if k < j:
if hermitian:
summ += C[j, k]*C[j, k].conjugate()
else:
summ += C[j, k]**2
else:
break
Cjj2 = dps(C[j, j] - summ)
if hermitian and Cjj2.is_positive is False:
raise NonPositiveDefiniteMatrixError(
"Matrix must be positive-definite")
C[j, j] = sqrt(Cjj2)
return M._new(C)
def _LDLdecomposition(M, hermitian=True):
"""Returns the LDL Decomposition (L, D) of matrix A,
such that L * D * L.H == A if hermitian flag is True, or
L * D * L.T == A if hermitian is False.
This method eliminates the use of square root.
Further this ensures that all the diagonal entries of L are 1.
A must be a Hermitian positive-definite matrix if hermitian is True,
or a symmetric matrix otherwise.
Examples
========
>>> from sympy import Matrix, eye
>>> A = Matrix(((25, 15, -5), (15, 18, 0), (-5, 0, 11)))
>>> L, D = A.LDLdecomposition()
>>> L
Matrix([
[ 1, 0, 0],
[ 3/5, 1, 0],
[-1/5, 1/3, 1]])
>>> D
Matrix([
[25, 0, 0],
[ 0, 9, 0],
[ 0, 0, 9]])
>>> L * D * L.T * A.inv() == eye(A.rows)
True
The matrix can have complex entries:
>>> from sympy import I
>>> A = Matrix(((9, 3*I), (-3*I, 5)))
>>> L, D = A.LDLdecomposition()
>>> L
Matrix([
[ 1, 0],
[-I/3, 1]])
>>> D
Matrix([
[9, 0],
[0, 4]])
>>> L*D*L.H == A
True
See Also
========
sympy.matrices.dense.DenseMatrix.cholesky
sympy.matrices.matrices.MatrixBase.LUdecomposition
QRdecomposition
"""
from .dense import MutableDenseMatrix
if not M.is_square:
raise NonSquareMatrixError("Matrix must be square.")
if hermitian and not M.is_hermitian:
raise ValueError("Matrix must be Hermitian.")
if not hermitian and not M.is_symmetric():
raise ValueError("Matrix must be symmetric.")
D = MutableDenseMatrix.zeros(M.rows, M.rows)
L = MutableDenseMatrix.eye(M.rows)
if hermitian:
for i in range(M.rows):
for j in range(i):
L[i, j] = (1 / D[j, j])*(M[i, j] - sum(
L[i, k]*L[j, k].conjugate()*D[k, k] for k in range(j)))
D[i, i] = (M[i, i] -
sum(L[i, k]*L[i, k].conjugate()*D[k, k] for k in range(i)))
if D[i, i].is_positive is False:
raise NonPositiveDefiniteMatrixError(
"Matrix must be positive-definite")
else:
for i in range(M.rows):
for j in range(i):
L[i, j] = (1 / D[j, j])*(M[i, j] - sum(
L[i, k]*L[j, k]*D[k, k] for k in range(j)))
D[i, i] = M[i, i] - sum(L[i, k]**2*D[k, k] for k in range(i))
return M._new(L), M._new(D)
def _LDLdecomposition_sparse(M, hermitian=True):
"""
Returns the LDL Decomposition (matrices ``L`` and ``D``) of matrix
``A``, such that ``L * D * L.T == A``. ``A`` must be a square,
symmetric, positive-definite and non-singular.
This method eliminates the use of square root and ensures that all
the diagonal entries of L are 1.
Examples
========
>>> from sympy import SparseMatrix
>>> A = SparseMatrix(((25, 15, -5), (15, 18, 0), (-5, 0, 11)))
>>> L, D = A.LDLdecomposition()
>>> L
Matrix([
[ 1, 0, 0],
[ 3/5, 1, 0],
[-1/5, 1/3, 1]])
>>> D
Matrix([
[25, 0, 0],
[ 0, 9, 0],
[ 0, 0, 9]])
>>> L * D * L.T == A
True
"""
from .dense import MutableDenseMatrix
if not M.is_square:
raise NonSquareMatrixError("Matrix must be square.")
if hermitian and not M.is_hermitian:
raise ValueError("Matrix must be Hermitian.")
if not hermitian and not M.is_symmetric():
raise ValueError("Matrix must be symmetric.")
dps = _get_intermediate_simp(expand_mul, expand_mul)
Lrowstruc = M.row_structure_symbolic_cholesky()
L = MutableDenseMatrix.eye(M.rows)
D = MutableDenseMatrix.zeros(M.rows, M.cols)
for i in range(len(Lrowstruc)):
for j in Lrowstruc[i]:
if i != j:
L[i, j] = M[i, j]
summ = 0
for p1 in Lrowstruc[i]:
if p1 < j:
for p2 in Lrowstruc[j]:
if p2 < j:
if p1 == p2:
if hermitian:
summ += L[i, p1]*L[j, p1].conjugate()*D[p1, p1]
else:
summ += L[i, p1]*L[j, p1]*D[p1, p1]
else:
break
else:
break
L[i, j] = dps((L[i, j] - summ) / D[j, j])
else: # i == j
D[i, i] = M[i, i]
summ = 0
for k in Lrowstruc[i]:
if k < i:
if hermitian:
summ += L[i, k]*L[i, k].conjugate()*D[k, k]
else:
summ += L[i, k]**2*D[k, k]
else:
break
D[i, i] = dps(D[i, i] - summ)
if hermitian and D[i, i].is_positive is False:
raise NonPositiveDefiniteMatrixError(
"Matrix must be positive-definite")
return M._new(L), M._new(D)
def _LUdecomposition(M, iszerofunc=_iszero, simpfunc=None, rankcheck=False):
"""Returns (L, U, perm) where L is a lower triangular matrix with unit
diagonal, U is an upper triangular matrix, and perm is a list of row
swap index pairs. If A is the original matrix, then
``A = (L*U).permuteBkwd(perm)``, and the row permutation matrix P such
that $P A = L U$ can be computed by ``P = eye(A.rows).permuteFwd(perm)``.
See documentation for LUCombined for details about the keyword argument
rankcheck, iszerofunc, and simpfunc.
Parameters
==========
rankcheck : bool, optional
Determines if this function should detect the rank
deficiency of the matrixis and should raise a
``ValueError``.
iszerofunc : function, optional
A function which determines if a given expression is zero.
The function should be a callable that takes a single
SymPy expression and returns a 3-valued boolean value
``True``, ``False``, or ``None``.
It is internally used by the pivot searching algorithm.
See the notes section for a more information about the
pivot searching algorithm.
simpfunc : function or None, optional
A function that simplifies the input.
If this is specified as a function, this function should be
a callable that takes a single SymPy expression and returns
an another SymPy expression that is algebraically
equivalent.
If ``None``, it indicates that the pivot search algorithm
should not attempt to simplify any candidate pivots.
It is internally used by the pivot searching algorithm.
See the notes section for a more information about the
pivot searching algorithm.
Examples
========
>>> from sympy import Matrix
>>> a = Matrix([[4, 3], [6, 3]])
>>> L, U, _ = a.LUdecomposition()
>>> L
Matrix([
[ 1, 0],
[3/2, 1]])
>>> U
Matrix([
[4, 3],
[0, -3/2]])
See Also
========
sympy.matrices.dense.DenseMatrix.cholesky
sympy.matrices.dense.DenseMatrix.LDLdecomposition
QRdecomposition
LUdecomposition_Simple
LUdecompositionFF
LUsolve
"""
combined, p = M.LUdecomposition_Simple(iszerofunc=iszerofunc,
simpfunc=simpfunc, rankcheck=rankcheck)
# L is lower triangular ``M.rows x M.rows``
# U is upper triangular ``M.rows x M.cols``
# L has unit diagonal. For each column in combined, the subcolumn
# below the diagonal of combined is shared by L.
# If L has more columns than combined, then the remaining subcolumns
# below the diagonal of L are zero.
# The upper triangular portion of L and combined are equal.
def entry_L(i, j):
if i < j:
# Super diagonal entry
return M.zero
elif i == j:
return M.one
elif j < combined.cols:
return combined[i, j]
# Subdiagonal entry of L with no corresponding
# entry in combined
return M.zero
def entry_U(i, j):
return M.zero if i > j else combined[i, j]
L = M._new(combined.rows, combined.rows, entry_L)
U = M._new(combined.rows, combined.cols, entry_U)
return L, U, p
def _LUdecomposition_Simple(M, iszerofunc=_iszero, simpfunc=None,
rankcheck=False):
r"""Compute the PLU decomposition of the matrix.
Parameters
==========
rankcheck : bool, optional
Determines if this function should detect the rank
deficiency of the matrixis and should raise a
``ValueError``.
iszerofunc : function, optional
A function which determines if a given expression is zero.
The function should be a callable that takes a single
SymPy expression and returns a 3-valued boolean value
``True``, ``False``, or ``None``.
It is internally used by the pivot searching algorithm.
See the notes section for a more information about the
pivot searching algorithm.
simpfunc : function or None, optional
A function that simplifies the input.
If this is specified as a function, this function should be
a callable that takes a single SymPy expression and returns
an another SymPy expression that is algebraically
equivalent.
If ``None``, it indicates that the pivot search algorithm
should not attempt to simplify any candidate pivots.
It is internally used by the pivot searching algorithm.
See the notes section for a more information about the
pivot searching algorithm.
Returns
=======
(lu, row_swaps) : (Matrix, list)
If the original matrix is a $m, n$ matrix:
*lu* is a $m, n$ matrix, which contains result of the
decomposition in a compressed form. See the notes section
to see how the matrix is compressed.
*row_swaps* is a $m$-element list where each element is a
pair of row exchange indices.
``A = (L*U).permute_backward(perm)``, and the row
permutation matrix $P$ from the formula $P A = L U$ can be
computed by ``P=eye(A.row).permute_forward(perm)``.
Raises
======
ValueError
Raised if ``rankcheck=True`` and the matrix is found to
be rank deficient during the computation.
Notes
=====
About the PLU decomposition:
PLU decomposition is a generalization of a LU decomposition
which can be extended for rank-deficient matrices.
It can further be generalized for non-square matrices, and this
is the notation that SymPy is using.
PLU decomposition is a decomposition of a $m, n$ matrix $A$ in
the form of $P A = L U$ where
* $L$ is a $m, m$ lower triangular matrix with unit diagonal
entries.
* $U$ is a $m, n$ upper triangular matrix.
* $P$ is a $m, m$ permutation matrix.
So, for a square matrix, the decomposition would look like:
.. math::
L = \begin{bmatrix}
1 & 0 & 0 & \cdots & 0 \\
L_{1, 0} & 1 & 0 & \cdots & 0 \\
L_{2, 0} & L_{2, 1} & 1 & \cdots & 0 \\
\vdots & \vdots & \vdots & \ddots & \vdots \\
L_{n-1, 0} & L_{n-1, 1} & L_{n-1, 2} & \cdots & 1
\end{bmatrix}
.. math::
U = \begin{bmatrix}
U_{0, 0} & U_{0, 1} & U_{0, 2} & \cdots & U_{0, n-1} \\
0 & U_{1, 1} & U_{1, 2} & \cdots & U_{1, n-1} \\
0 & 0 & U_{2, 2} & \cdots & U_{2, n-1} \\
\vdots & \vdots & \vdots & \ddots & \vdots \\
0 & 0 & 0 & \cdots & U_{n-1, n-1}
\end{bmatrix}
And for a matrix with more rows than the columns,
the decomposition would look like:
.. math::
L = \begin{bmatrix}
1 & 0 & 0 & \cdots & 0 & 0 & \cdots & 0 \\
L_{1, 0} & 1 & 0 & \cdots & 0 & 0 & \cdots & 0 \\
L_{2, 0} & L_{2, 1} & 1 & \cdots & 0 & 0 & \cdots & 0 \\
\vdots & \vdots & \vdots & \ddots & \vdots & \vdots & \ddots
& \vdots \\
L_{n-1, 0} & L_{n-1, 1} & L_{n-1, 2} & \cdots & 1 & 0
& \cdots & 0 \\
L_{n, 0} & L_{n, 1} & L_{n, 2} & \cdots & L_{n, n-1} & 1
& \cdots & 0 \\
\vdots & \vdots & \vdots & \ddots & \vdots & \vdots
& \ddots & \vdots \\
L_{m-1, 0} & L_{m-1, 1} & L_{m-1, 2} & \cdots & L_{m-1, n-1}
& 0 & \cdots & 1 \\
\end{bmatrix}
.. math::
U = \begin{bmatrix}
U_{0, 0} & U_{0, 1} & U_{0, 2} & \cdots & U_{0, n-1} \\
0 & U_{1, 1} & U_{1, 2} & \cdots & U_{1, n-1} \\
0 & 0 & U_{2, 2} & \cdots & U_{2, n-1} \\
\vdots & \vdots & \vdots & \ddots & \vdots \\
0 & 0 & 0 & \cdots & U_{n-1, n-1} \\
0 & 0 & 0 & \cdots & 0 \\
\vdots & \vdots & \vdots & \ddots & \vdots \\
0 & 0 & 0 & \cdots & 0
\end{bmatrix}
Finally, for a matrix with more columns than the rows, the
decomposition would look like:
.. math::
L = \begin{bmatrix}
1 & 0 & 0 & \cdots & 0 \\
L_{1, 0} & 1 & 0 & \cdots & 0 \\
L_{2, 0} & L_{2, 1} & 1 & \cdots & 0 \\
\vdots & \vdots & \vdots & \ddots & \vdots \\
L_{m-1, 0} & L_{m-1, 1} & L_{m-1, 2} & \cdots & 1
\end{bmatrix}
.. math::
U = \begin{bmatrix}
U_{0, 0} & U_{0, 1} & U_{0, 2} & \cdots & U_{0, m-1}
& \cdots & U_{0, n-1} \\
0 & U_{1, 1} & U_{1, 2} & \cdots & U_{1, m-1}
& \cdots & U_{1, n-1} \\
0 & 0 & U_{2, 2} & \cdots & U_{2, m-1}
& \cdots & U_{2, n-1} \\
\vdots & \vdots & \vdots & \ddots & \vdots
& \cdots & \vdots \\
0 & 0 & 0 & \cdots & U_{m-1, m-1}
& \cdots & U_{m-1, n-1} \\
\end{bmatrix}
About the compressed LU storage:
The results of the decomposition are often stored in compressed
forms rather than returning $L$ and $U$ matrices individually.
It may be less intiuitive, but it is commonly used for a lot of
numeric libraries because of the efficiency.
The storage matrix is defined as following for this specific
method:
* The subdiagonal elements of $L$ are stored in the subdiagonal
portion of $LU$, that is $LU_{i, j} = L_{i, j}$ whenever
$i > j$.
* The elements on the diagonal of $L$ are all 1, and are not
explicitly stored.
* $U$ is stored in the upper triangular portion of $LU$, that is
$LU_{i, j} = U_{i, j}$ whenever $i <= j$.
* For a case of $m > n$, the right side of the $L$ matrix is
trivial to store.
* For a case of $m < n$, the below side of the $U$ matrix is
trivial to store.
So, for a square matrix, the compressed output matrix would be:
.. math::
LU = \begin{bmatrix}
U_{0, 0} & U_{0, 1} & U_{0, 2} & \cdots & U_{0, n-1} \\
L_{1, 0} & U_{1, 1} & U_{1, 2} & \cdots & U_{1, n-1} \\
L_{2, 0} & L_{2, 1} & U_{2, 2} & \cdots & U_{2, n-1} \\
\vdots & \vdots & \vdots & \ddots & \vdots \\
L_{n-1, 0} & L_{n-1, 1} & L_{n-1, 2} & \cdots & U_{n-1, n-1}
\end{bmatrix}
For a matrix with more rows than the columns, the compressed
output matrix would be:
.. math::
LU = \begin{bmatrix}
U_{0, 0} & U_{0, 1} & U_{0, 2} & \cdots & U_{0, n-1} \\
L_{1, 0} & U_{1, 1} & U_{1, 2} & \cdots & U_{1, n-1} \\
L_{2, 0} & L_{2, 1} & U_{2, 2} & \cdots & U_{2, n-1} \\
\vdots & \vdots & \vdots & \ddots & \vdots \\
L_{n-1, 0} & L_{n-1, 1} & L_{n-1, 2} & \cdots
& U_{n-1, n-1} \\
\vdots & \vdots & \vdots & \ddots & \vdots \\
L_{m-1, 0} & L_{m-1, 1} & L_{m-1, 2} & \cdots
& L_{m-1, n-1} \\
\end{bmatrix}
For a matrix with more columns than the rows, the compressed
output matrix would be:
.. math::
LU = \begin{bmatrix}
U_{0, 0} & U_{0, 1} & U_{0, 2} & \cdots & U_{0, m-1}
& \cdots & U_{0, n-1} \\
L_{1, 0} & U_{1, 1} & U_{1, 2} & \cdots & U_{1, m-1}
& \cdots & U_{1, n-1} \\
L_{2, 0} & L_{2, 1} & U_{2, 2} & \cdots & U_{2, m-1}
& \cdots & U_{2, n-1} \\
\vdots & \vdots & \vdots & \ddots & \vdots
& \cdots & \vdots \\
L_{m-1, 0} & L_{m-1, 1} & L_{m-1, 2} & \cdots & U_{m-1, m-1}
& \cdots & U_{m-1, n-1} \\
\end{bmatrix}
About the pivot searching algorithm:
When a matrix contains symbolic entries, the pivot search algorithm
differs from the case where every entry can be categorized as zero or
nonzero.
The algorithm searches column by column through the submatrix whose
top left entry coincides with the pivot position.
If it exists, the pivot is the first entry in the current search
column that iszerofunc guarantees is nonzero.
If no such candidate exists, then each candidate pivot is simplified
if simpfunc is not None.
The search is repeated, with the difference that a candidate may be
the pivot if ``iszerofunc()`` cannot guarantee that it is nonzero.
In the second search the pivot is the first candidate that
iszerofunc can guarantee is nonzero.
If no such candidate exists, then the pivot is the first candidate
for which iszerofunc returns None.
If no such candidate exists, then the search is repeated in the next
column to the right.
The pivot search algorithm differs from the one in ``rref()``, which
relies on ``_find_reasonable_pivot()``.
Future versions of ``LUdecomposition_simple()`` may use
``_find_reasonable_pivot()``.
See Also
========
sympy.matrices.matrices.MatrixBase.LUdecomposition
LUdecompositionFF
LUsolve
"""
if rankcheck:
# https://github.com/sympy/sympy/issues/9796
pass
if S.Zero in M.shape:
# Define LU decomposition of a matrix with no entries as a matrix
# of the same dimensions with all zero entries.
return M.zeros(M.rows, M.cols), []
dps = _get_intermediate_simp()
lu = M.as_mutable()
row_swaps = []
pivot_col = 0
for pivot_row in range(0, lu.rows - 1):
# Search for pivot. Prefer entry that iszeropivot determines
# is nonzero, over entry that iszeropivot cannot guarantee
# is zero.
# XXX ``_find_reasonable_pivot`` uses slow zero testing. Blocked by bug #10279
# Future versions of LUdecomposition_simple can pass iszerofunc and simpfunc
# to _find_reasonable_pivot().
# In pass 3 of _find_reasonable_pivot(), the predicate in ``if x.equals(S.Zero):``
# calls sympy.simplify(), and not the simplification function passed in via
# the keyword argument simpfunc.
iszeropivot = True
while pivot_col != M.cols and iszeropivot:
sub_col = (lu[r, pivot_col] for r in range(pivot_row, M.rows))
pivot_row_offset, pivot_value, is_assumed_non_zero, ind_simplified_pairs =\
_find_reasonable_pivot_naive(sub_col, iszerofunc, simpfunc)
iszeropivot = pivot_value is None
if iszeropivot:
# All candidate pivots in this column are zero.
# Proceed to next column.
pivot_col += 1
if rankcheck and pivot_col != pivot_row:
# All entries including and below the pivot position are
# zero, which indicates that the rank of the matrix is
# strictly less than min(num rows, num cols)
# Mimic behavior of previous implementation, by throwing a
# ValueError.
raise ValueError("Rank of matrix is strictly less than"
" number of rows or columns."
" Pass keyword argument"
" rankcheck=False to compute"
" the LU decomposition of this matrix.")
candidate_pivot_row = None if pivot_row_offset is None else pivot_row + pivot_row_offset
if candidate_pivot_row is None and iszeropivot:
# If candidate_pivot_row is None and iszeropivot is True
# after pivot search has completed, then the submatrix
# below and to the right of (pivot_row, pivot_col) is
# all zeros, indicating that Gaussian elimination is
# complete.
return lu, row_swaps
# Update entries simplified during pivot search.
for offset, val in ind_simplified_pairs:
lu[pivot_row + offset, pivot_col] = val
if pivot_row != candidate_pivot_row:
# Row swap book keeping:
# Record which rows were swapped.
# Update stored portion of L factor by multiplying L on the
# left and right with the current permutation.
# Swap rows of U.
row_swaps.append([pivot_row, candidate_pivot_row])
# Update L.
lu[pivot_row, 0:pivot_row], lu[candidate_pivot_row, 0:pivot_row] = \
lu[candidate_pivot_row, 0:pivot_row], lu[pivot_row, 0:pivot_row]
# Swap pivot row of U with candidate pivot row.
lu[pivot_row, pivot_col:lu.cols], lu[candidate_pivot_row, pivot_col:lu.cols] = \
lu[candidate_pivot_row, pivot_col:lu.cols], lu[pivot_row, pivot_col:lu.cols]
# Introduce zeros below the pivot by adding a multiple of the
# pivot row to a row under it, and store the result in the
# row under it.
# Only entries in the target row whose index is greater than
# start_col may be nonzero.
start_col = pivot_col + 1
for row in range(pivot_row + 1, lu.rows):
# Store factors of L in the subcolumn below
# (pivot_row, pivot_row).
lu[row, pivot_row] = \
dps(lu[row, pivot_col]/lu[pivot_row, pivot_col])
# Form the linear combination of the pivot row and the current
# row below the pivot row that zeros the entries below the pivot.
# Employing slicing instead of a loop here raises
# NotImplementedError: Cannot add Zero to MutableSparseMatrix
# in sympy/matrices/tests/test_sparse.py.
# c = pivot_row + 1 if pivot_row == pivot_col else pivot_col
for c in range(start_col, lu.cols):
lu[row, c] = dps(lu[row, c] - lu[row, pivot_row]*lu[pivot_row, c])
if pivot_row != pivot_col:
# matrix rank < min(num rows, num cols),
# so factors of L are not stored directly below the pivot.
# These entries are zero by construction, so don't bother
# computing them.
for row in range(pivot_row + 1, lu.rows):
lu[row, pivot_col] = M.zero
pivot_col += 1
if pivot_col == lu.cols:
# All candidate pivots are zero implies that Gaussian
# elimination is complete.
return lu, row_swaps
if rankcheck:
if iszerofunc(
lu[Min(lu.rows, lu.cols) - 1, Min(lu.rows, lu.cols) - 1]):
raise ValueError("Rank of matrix is strictly less than"
" number of rows or columns."
" Pass keyword argument"
" rankcheck=False to compute"
" the LU decomposition of this matrix.")
return lu, row_swaps
def _LUdecompositionFF(M):
"""Compute a fraction-free LU decomposition.
Returns 4 matrices P, L, D, U such that PA = L D**-1 U.
If the elements of the matrix belong to some integral domain I, then all
elements of L, D and U are guaranteed to belong to I.
See Also
========
sympy.matrices.matrices.MatrixBase.LUdecomposition
LUdecomposition_Simple
LUsolve
References
==========
.. [1] W. Zhou & D.J. Jeffrey, "Fraction-free matrix factors: new forms
for LU and QR factors". Frontiers in Computer Science in China,
Vol 2, no. 1, pp. 67-80, 2008.
"""
from sympy.matrices import SparseMatrix
zeros = SparseMatrix.zeros
eye = SparseMatrix.eye
n, m = M.rows, M.cols
U, L, P = M.as_mutable(), eye(n), eye(n)
DD = zeros(n, n)
oldpivot = 1
for k in range(n - 1):
if U[k, k] == 0:
for kpivot in range(k + 1, n):
if U[kpivot, k]:
break
else:
raise ValueError("Matrix is not full rank")
U[k, k:], U[kpivot, k:] = U[kpivot, k:], U[k, k:]
L[k, :k], L[kpivot, :k] = L[kpivot, :k], L[k, :k]
P[k, :], P[kpivot, :] = P[kpivot, :], P[k, :]
L [k, k] = Ukk = U[k, k]
DD[k, k] = oldpivot * Ukk
for i in range(k + 1, n):
L[i, k] = Uik = U[i, k]
for j in range(k + 1, m):
U[i, j] = (Ukk * U[i, j] - U[k, j] * Uik) / oldpivot
U[i, k] = 0
oldpivot = Ukk
DD[n - 1, n - 1] = oldpivot
return P, L, DD, U
def _singular_value_decomposition(A):
r"""Returns a Condensed Singular Value decomposition.
Explanation
===========
A Singular Value decomposition is a decomposition in the form $A = U \Sigma V$
where
- $U, V$ are column orthogonal matrix.
- $\Sigma$ is a diagonal matrix, where the main diagonal contains singular
values of matrix A.
A column orthogonal matrix satisfies
$\mathbb{I} = U^H U$ while a full orthogonal matrix satisfies
relation $\mathbb{I} = U U^H = U^H U$ where $\mathbb{I}$ is an identity
matrix with matching dimensions.
For matrices which are not square or are rank-deficient, it is
sufficient to return a column orthogonal matrix because augmenting
them may introduce redundant computations.
In condensed Singular Value Decomposition we only return column orthogonal
matrices because of this reason
If you want to augment the results to return a full orthogonal
decomposition, you should use the following procedures.
- Augment the $U, V$ matrices with columns that are orthogonal to every
other columns and make it square.
- Augment the $\Sigma$ matrix with zero rows to make it have the same
shape as the original matrix.
The procedure will be illustrated in the examples section.
Examples
========
we take a full rank matrix first:
>>> from sympy import Matrix
>>> A = Matrix([[1, 2],[2,1]])
>>> U, S, V = A.singular_value_decomposition()
>>> U
Matrix([
[ sqrt(2)/2, sqrt(2)/2],
[-sqrt(2)/2, sqrt(2)/2]])
>>> S
Matrix([
[1, 0],
[0, 3]])
>>> V
Matrix([
[-sqrt(2)/2, sqrt(2)/2],
[ sqrt(2)/2, sqrt(2)/2]])
If a matrix if square and full rank both U, V
are orthogonal in both directions
>>> U * U.H
Matrix([
[1, 0],
[0, 1]])
>>> U.H * U
Matrix([
[1, 0],
[0, 1]])
>>> V * V.H
Matrix([
[1, 0],
[0, 1]])
>>> V.H * V
Matrix([
[1, 0],
[0, 1]])
>>> A == U * S * V.H
True
>>> C = Matrix([
... [1, 0, 0, 0, 2],
... [0, 0, 3, 0, 0],
... [0, 0, 0, 0, 0],
... [0, 2, 0, 0, 0],
... ])
>>> U, S, V = C.singular_value_decomposition()
>>> V.H * V
Matrix([
[1, 0, 0],
[0, 1, 0],
[0, 0, 1]])
>>> V * V.H
Matrix([
[1/5, 0, 0, 0, 2/5],
[ 0, 1, 0, 0, 0],
[ 0, 0, 1, 0, 0],
[ 0, 0, 0, 0, 0],
[2/5, 0, 0, 0, 4/5]])
If you want to augment the results to be a full orthogonal
decomposition, you should augment $V$ with an another orthogonal
column.
You are able to append an arbitrary standard basis that are linearly
independent to every other columns and you can run the Gram-Schmidt
process to make them augmented as orthogonal basis.
>>> V_aug = V.row_join(Matrix([[0,0,0,0,1],
... [0,0,0,1,0]]).H)
>>> V_aug = V_aug.QRdecomposition()[0]
>>> V_aug
Matrix([
[0, sqrt(5)/5, 0, -2*sqrt(5)/5, 0],
[1, 0, 0, 0, 0],
[0, 0, 1, 0, 0],
[0, 0, 0, 0, 1],
[0, 2*sqrt(5)/5, 0, sqrt(5)/5, 0]])
>>> V_aug.H * V_aug
Matrix([
[1, 0, 0, 0, 0],
[0, 1, 0, 0, 0],
[0, 0, 1, 0, 0],
[0, 0, 0, 1, 0],
[0, 0, 0, 0, 1]])
>>> V_aug * V_aug.H
Matrix([
[1, 0, 0, 0, 0],
[0, 1, 0, 0, 0],
[0, 0, 1, 0, 0],
[0, 0, 0, 1, 0],
[0, 0, 0, 0, 1]])
Similarly we augment U
>>> U_aug = U.row_join(Matrix([0,0,1,0]))
>>> U_aug = U_aug.QRdecomposition()[0]
>>> U_aug
Matrix([
[0, 1, 0, 0],
[0, 0, 1, 0],
[0, 0, 0, 1],
[1, 0, 0, 0]])
>>> U_aug.H * U_aug
Matrix([
[1, 0, 0, 0],
[0, 1, 0, 0],
[0, 0, 1, 0],
[0, 0, 0, 1]])
>>> U_aug * U_aug.H
Matrix([
[1, 0, 0, 0],
[0, 1, 0, 0],
[0, 0, 1, 0],
[0, 0, 0, 1]])
We add 2 zero columns and one row to S
>>> S_aug = S.col_join(Matrix([[0,0,0]]))
>>> S_aug = S_aug.row_join(Matrix([[0,0,0,0],
... [0,0,0,0]]).H)
>>> S_aug
Matrix([
[2, 0, 0, 0, 0],
[0, sqrt(5), 0, 0, 0],
[0, 0, 3, 0, 0],
[0, 0, 0, 0, 0]])
>>> U_aug * S_aug * V_aug.H == C
True
"""
AH = A.H
m, n = A.shape
if m >= n:
V, S = (AH * A).diagonalize()
ranked = []
for i, x in enumerate(S.diagonal()):
if not x.is_zero:
ranked.append(i)
V = V[:, ranked]
Singular_vals = [sqrt(S[i, i]) for i in range(S.rows) if i in ranked]
S = S.zeros(len(Singular_vals))
for i, sv in enumerate(Singular_vals):
S[i, i] = sv
V, _ = V.QRdecomposition()
U = A * V * S.inv()
else:
U, S = (A * AH).diagonalize()
ranked = []
for i, x in enumerate(S.diagonal()):
if not x.is_zero:
ranked.append(i)
U = U[:, ranked]
Singular_vals = [sqrt(S[i, i]) for i in range(S.rows) if i in ranked]
S = S.zeros(len(Singular_vals))
for i, sv in enumerate(Singular_vals):
S[i, i] = sv
U, _ = U.QRdecomposition()
V = AH * U * S.inv()
return U, S, V
def _QRdecomposition_optional(M, normalize=True):
def dot(u, v):
return u.dot(v, hermitian=True)
dps = _get_intermediate_simp(expand_mul, expand_mul)
A = M.as_mutable()
ranked = []
Q = A
R = A.zeros(A.cols)
for j in range(A.cols):
for i in range(j):
if Q[:, i].is_zero_matrix:
continue
R[i, j] = dot(Q[:, i], Q[:, j]) / dot(Q[:, i], Q[:, i])
R[i, j] = dps(R[i, j])
Q[:, j] -= Q[:, i] * R[i, j]
Q[:, j] = dps(Q[:, j])
if Q[:, j].is_zero_matrix is not True:
ranked.append(j)
R[j, j] = M.one
Q = Q.extract(range(Q.rows), ranked)
R = R.extract(ranked, range(R.cols))
if normalize:
# Normalization
for i in range(Q.cols):
norm = Q[:, i].norm()
Q[:, i] /= norm
R[i, :] *= norm
return M.__class__(Q), M.__class__(R)
def _QRdecomposition(M):
r"""Returns a QR decomposition.
Explanation
===========
A QR decomposition is a decomposition in the form $A = Q R$
where
- $Q$ is a column orthogonal matrix.
- $R$ is a upper triangular (trapezoidal) matrix.
A column orthogonal matrix satisfies
$\mathbb{I} = Q^H Q$ while a full orthogonal matrix satisfies
relation $\mathbb{I} = Q Q^H = Q^H Q$ where $I$ is an identity
matrix with matching dimensions.
For matrices which are not square or are rank-deficient, it is
sufficient to return a column orthogonal matrix because augmenting
them may introduce redundant computations.
And an another advantage of this is that you can easily inspect the
matrix rank by counting the number of columns of $Q$.
If you want to augment the results to return a full orthogonal
decomposition, you should use the following procedures.
- Augment the $Q$ matrix with columns that are orthogonal to every
other columns and make it square.
- Augment the $R$ matrix with zero rows to make it have the same
shape as the original matrix.
The procedure will be illustrated in the examples section.
Examples
========
A full rank matrix example:
>>> from sympy import Matrix
>>> A = Matrix([[12, -51, 4], [6, 167, -68], [-4, 24, -41]])
>>> Q, R = A.QRdecomposition()
>>> Q
Matrix([
[ 6/7, -69/175, -58/175],
[ 3/7, 158/175, 6/175],
[-2/7, 6/35, -33/35]])
>>> R
Matrix([
[14, 21, -14],
[ 0, 175, -70],
[ 0, 0, 35]])
If the matrix is square and full rank, the $Q$ matrix becomes
orthogonal in both directions, and needs no augmentation.
>>> Q * Q.H
Matrix([
[1, 0, 0],
[0, 1, 0],
[0, 0, 1]])
>>> Q.H * Q
Matrix([
[1, 0, 0],
[0, 1, 0],
[0, 0, 1]])
>>> A == Q*R
True
A rank deficient matrix example:
>>> A = Matrix([[12, -51, 0], [6, 167, 0], [-4, 24, 0]])
>>> Q, R = A.QRdecomposition()
>>> Q
Matrix([
[ 6/7, -69/175],
[ 3/7, 158/175],
[-2/7, 6/35]])
>>> R
Matrix([
[14, 21, 0],
[ 0, 175, 0]])
QRdecomposition might return a matrix Q that is rectangular.
In this case the orthogonality condition might be satisfied as
$\mathbb{I} = Q.H*Q$ but not in the reversed product
$\mathbb{I} = Q * Q.H$.
>>> Q.H * Q
Matrix([
[1, 0],
[0, 1]])
>>> Q * Q.H
Matrix([
[27261/30625, 348/30625, -1914/6125],
[ 348/30625, 30589/30625, 198/6125],
[ -1914/6125, 198/6125, 136/1225]])
If you want to augment the results to be a full orthogonal
decomposition, you should augment $Q$ with an another orthogonal
column.
You are able to append an arbitrary standard basis that are linearly
independent to every other columns and you can run the Gram-Schmidt
process to make them augmented as orthogonal basis.
>>> Q_aug = Q.row_join(Matrix([0, 0, 1]))
>>> Q_aug = Q_aug.QRdecomposition()[0]
>>> Q_aug
Matrix([
[ 6/7, -69/175, 58/175],
[ 3/7, 158/175, -6/175],
[-2/7, 6/35, 33/35]])
>>> Q_aug.H * Q_aug
Matrix([
[1, 0, 0],
[0, 1, 0],
[0, 0, 1]])
>>> Q_aug * Q_aug.H
Matrix([
[1, 0, 0],
[0, 1, 0],
[0, 0, 1]])
Augmenting the $R$ matrix with zero row is straightforward.
>>> R_aug = R.col_join(Matrix([[0, 0, 0]]))
>>> R_aug
Matrix([
[14, 21, 0],
[ 0, 175, 0],
[ 0, 0, 0]])
>>> Q_aug * R_aug == A
True
A zero matrix example:
>>> from sympy import Matrix
>>> A = Matrix.zeros(3, 4)
>>> Q, R = A.QRdecomposition()
They may return matrices with zero rows and columns.
>>> Q
Matrix(3, 0, [])
>>> R
Matrix(0, 4, [])
>>> Q*R
Matrix([
[0, 0, 0, 0],
[0, 0, 0, 0],
[0, 0, 0, 0]])
As the same augmentation rule described above, $Q$ can be augmented
with columns of an identity matrix and $R$ can be augmented with
rows of a zero matrix.
>>> Q_aug = Q.row_join(Matrix.eye(3))
>>> R_aug = R.col_join(Matrix.zeros(3, 4))
>>> Q_aug * Q_aug.T
Matrix([
[1, 0, 0],
[0, 1, 0],
[0, 0, 1]])
>>> R_aug
Matrix([
[0, 0, 0, 0],
[0, 0, 0, 0],
[0, 0, 0, 0]])
>>> Q_aug * R_aug == A
True
See Also
========
sympy.matrices.dense.DenseMatrix.cholesky
sympy.matrices.dense.DenseMatrix.LDLdecomposition
sympy.matrices.matrices.MatrixBase.LUdecomposition
QRsolve
"""
return _QRdecomposition_optional(M, normalize=True)
def _upper_hessenberg_decomposition(A):
"""Converts a matrix into Hessenberg matrix H.
Returns 2 matrices H, P s.t.
$P H P^{T} = A$, where H is an upper hessenberg matrix
and P is an orthogonal matrix
Examples
========
>>> from sympy import Matrix
>>> A = Matrix([
... [1,2,3],
... [-3,5,6],
... [4,-8,9],
... ])
>>> H, P = A.upper_hessenberg_decomposition()
>>> H
Matrix([
[1, 6/5, 17/5],
[5, 213/25, -134/25],
[0, 216/25, 137/25]])
>>> P
Matrix([
[1, 0, 0],
[0, -3/5, 4/5],
[0, 4/5, 3/5]])
>>> P * H * P.H == A
True
References
==========
.. [#] https://mathworld.wolfram.com/HessenbergDecomposition.html
"""
M = A.as_mutable()
if not M.is_square:
raise NonSquareMatrixError("Matrix must be square.")
n = M.cols
P = M.eye(n)
H = M
for j in range(n - 2):
u = H[j + 1:, j]
if u[1:, :].is_zero_matrix:
continue
if sign(u[0]) != 0:
u[0] = u[0] + sign(u[0]) * u.norm()
else:
u[0] = u[0] + u.norm()
v = u / u.norm()
H[j + 1:, :] = H[j + 1:, :] - 2 * v * (v.H * H[j + 1:, :])
H[:, j + 1:] = H[:, j + 1:] - (H[:, j + 1:] * (2 * v)) * v.H
P[:, j + 1:] = P[:, j + 1:] - (P[:, j + 1:] * (2 * v)) * v.H
return H, P
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