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e�Zddd�ZG dd� de�ZG dd� de�ZG dd� de�ZG dd� de�ZG dd� de�ZG dd� de�ZG dd� de�Zdd� ZdS ) a� Abstract linear algebra library.
This module defines a class hierarchy that implements a kind of "lazy"
matrix representation, called the ``LinearOperator``. It can be used to do
linear algebra with extremely large sparse or structured matrices, without
representing those explicitly in memory. Such matrices can be added,
multiplied, transposed, etc.
As a motivating example, suppose you want have a matrix where almost all of
the elements have the value one. The standard sparse matrix representation
skips the storage of zeros, but not ones. By contrast, a LinearOperator is
able to represent such matrices efficiently. First, we need a compact way to
represent an all-ones matrix::
>>> import numpy as np
>>> class Ones(LinearOperator):
... def __init__(self, shape):
... super().__init__(dtype=None, shape=shape)
... def _matvec(self, x):
... return np.repeat(x.sum(), self.shape[0])
Instances of this class emulate ``np.ones(shape)``, but using a constant
amount of storage, independent of ``shape``. The ``_matvec`` method specifies
how this linear operator multiplies with (operates on) a vector. We can now
add this operator to a sparse matrix that stores only offsets from one::
>>> from scipy.sparse import csr_matrix
>>> offsets = csr_matrix([[1, 0, 2], [0, -1, 0], [0, 0, 3]])
>>> A = aslinearoperator(offsets) + Ones(offsets.shape)
>>> A.dot([1, 2, 3])
array([13, 4, 15])
The result is the same as that given by its dense, explicitly-stored
counterpart::
>>> (np.ones(A.shape, A.dtype) + offsets.toarray()).dot([1, 2, 3])
array([13, 4, 15])
Several algorithms in the ``scipy.sparse`` library are able to operate on
``LinearOperator`` instances.
� N)�
isspmatrix)�isshape� isintlike�asmatrix�is_pydata_spmatrix�LinearOperator�aslinearoperatorc s� e Zd ZdZdZ� fdd�Zdd� Zdd� Zd d
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d� Z
dd� Zdd� Zdd� Z
dd� Zdd� Zdd� Zdd� Zdd� Zdd � Zd!d"� Zd#d$� Zd%d&� Zd'd(� Zd)d*� Zd+d,� Zd-d.� Zd/d0� Zee�Zd1d2� Zee�Zd3d4� Z d5d6� Z!� Z"S )7r aj 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.
To construct a concrete LinearOperator, either pass appropriate
callables to the constructor of this class, or subclass it.
A subclass must implement either one of the methods ``_matvec``
and ``_matmat``, and the attributes/properties ``shape`` (pair of
integers) and ``dtype`` (may be None). It may call the ``__init__``
on this class to have these attributes validated. Implementing
``_matvec`` automatically implements ``_matmat`` (using a naive
algorithm) and vice-versa.
Optionally, a subclass may implement ``_rmatvec`` or ``_adjoint``
to implement the Hermitian adjoint (conjugate transpose). As with
``_matvec`` and ``_matmat``, implementing either ``_rmatvec`` or
``_adjoint`` implements the other automatically. Implementing
``_adjoint`` is preferable; ``_rmatvec`` is mostly there for
backwards compatibility.
Parameters
----------
shape : tuple
Matrix dimensions (M, N).
matvec : callable f(v)
Returns returns A * v.
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.
rmatmat : callable f(V)
Returns A^H * V, where V is a dense matrix with dimensions (M, K).
Attributes
----------
args : tuple
For linear operators describing products etc. of other linear
operators, the operands of the binary operation.
ndim : int
Number of dimensions (this is always 2)
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, all lazily: the result of these operations
is always a new, composite LinearOperator, that defers linear
operations to the original operators and combines the results.
More details regarding how to subclass a LinearOperator and several
examples of concrete LinearOperator instances can be found in the
external project `PyLops <https://pylops.readthedocs.io>`_.
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 _CustomLinearOperator with dtype=float64>
>>> A.matvec(np.ones(2))
array([ 2., 3.])
>>> A * np.ones(2)
array([ 2., 3.])
� c s\ | t u rtt | ��t�S tt | ��| �}t|�jt jkr,t|�jt jkr,tjdt dd� |S )NzMLinearOperator subclass should implement at least one of _matvec and _matmat.r )�category�
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� s �zLinearOperator.__new__c C s@ |dur t �|�}t|�}t|�std|f ��|| _|| _dS )z�Initialize this LinearOperator.
To be called by subclasses. ``dtype`` may be None; ``shape`` should
be convertible to a length-2 tuple.
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