scipy.sparse.linalg.LinearOperator

class scipy.sparse.linalg.LinearOperator(shape, matvec, rmatvec=None, matmat=None, dtype=None)

Common interface for performing matrix vector products

Many iterative methods (e.g. cg, gmres) do not need to know the individual entries of a matrix to solve a linear system A*x=b. Such solvers only require the computation of matrix vector products, A*v where v is a dense vector. This class serves as an abstract interface between iterative solvers and matrix-like objects.

Parameters:

shape : tuple

Matrix dimensions (M,N)

matvec : callable f(v)

Returns returns A * v.

Other Parameters:  

rmatvec : callable f(v)

Returns A^H * v, where A^H is the conjugate transpose of A.

matmat : callable f(V)

Returns A * V, where V is a dense matrix with dimensions (N,K).

dtype : dtype

Data type of the matrix.

See also

aslinearoperator

Construct LinearOperators

Notes

The user-defined matvec() function must properly handle the case where v has shape (N,) as well as the (N,1) case. The shape of the return type is handled internally by LinearOperator.

LinearOperator instances can also be multiplied, added with each other and exponentiated, to produce a new linear operator.

Examples

>>> import numpy as np
>>> from scipy.sparse.linalg import LinearOperator
>>> def mv(v):
...     return np.array([2*v[0], 3*v[1]])
...
>>> A = LinearOperator((2,2), matvec=mv)
>>> A
<2x2 LinearOperator with unspecified dtype>
>>> A.matvec(np.ones(2))
array([ 2.,  3.])
>>> A * np.ones(2)
array([ 2.,  3.])

Attributes

args	(tuple) For linear operators describing products etc. of other linear operators, the operands of the binary operation.

Methods

__call__(x)
dot(other)
matmat(X)	Matrix-matrix multiplication
matvec(x)	Matrix-vector multiplication