1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
|
function S = inverse (A, varargin)
%INVERSE factorized representation of inv(A) or pinv(A).
% INVERSE is a fast and accurate replacement for INV or PINV when you want to
% solve a linear system or least squares problem, or when you want to multiply
% something by the inverse of A. The inverse itself is NOT computed, UNLESS
% the factorized form of the inverse is converted into a matrix via
% double(inverse(A)). If A is rectangular and has full rank, or rank deficient
% and COD is able to accurately estimate the rank, then inverse(A) is a
% factorized form of the pseudo-inverse of A, pinv(A).
%
% Example
%
% x = inv(A)*b ; % slow and inaccurate way to solve A*x=b
% x = inverse(A)*b ; % fast an accurate way to solve A*x=b (uses x=A\b)
% x = A\b ; % same as inverse(A)*b
%
% x1 = A\b1 ; x2 = A\b2 ; % accurate but slow
% S = inverse(A) ; x1 = S*b1 ; x2 = S*b1 ; % fast and accurate
% S = inv(A) ; x1 = S*b1 ; x2 = S*b1 ; % slow and inaccurate
%
% Z = double(inverse(A)) ; % same as Z=inv(A), computes the inverse of
% % A, returning Z as a matrix, not an object.
%
% F = factorize(A) ; % computes the factorization of A
% S = inverse(F) ; % no flops, flags S as a factorized form of inv(A)
%
% An optional 2nd input selects the strategy used to factorize the matrix,
% and an optional 3rd input tells the function to display how it factorizes
% the matrix. See the 'strategy' and 'burble' of the factorize function.
%
% Never use inv to multiply the inverse of a matrix A by another matrix.
% There are rare uses for the explicit inv(A), but never do inv(A)*B or
% B*inv(A). Never do Z=A\eye(n), which is just the same thing as Z=inv(A).
%
% "Don't let that inv go past your eyes; to solve that system, factorize!"
%
% See also factorize, slash, inv, pinv.
% Factorize, Copyright (c) 2011-2012, Timothy A Davis. All Rights Reserved.
% SPDX-License-Identifier: BSD-3-clause
% This function is only called when A is a matrix. If A is a factorize
% object, then factorize.inverse is called instead.
S = inverse (factorize (A, varargin {:})) ;
|
