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
|
function Y = spqr_qmult (H,X,method) %#ok
%SPQR_QMULT computes Q'*X, Q*X, X*Q', or X*Q with Q in Householder form.
% Usage: Y = spqr_qmult (Q,X,method)
%
% method = 0: Y = Q'*X default if 3rd input argument is not present.
% method = 1: Y = Q*X
% method = 2: Y = X*Q'
% method = 3: Y = X*Q
%
% where Q is the struct from [Q,R,E] = spqr (A,opts) with
% opts.Q = 'Householder'. The struct Q always represents a square
% orthonormal matrix, regardless of opts.econ. spqr_qmult applies this
% square matrix to compute Y.
%
% Example:
% These two examples both compute the min-norm solution to an
% under determined system, but the latter is much more efficient:
%
% [Q,R,E] = spqr(A') ; x = Q*(R'\(E'*b)) ;
%
% [Q,R,E] = spqr(A',struct('Q','Householder')) ;
% x = spqr_qmult(Q,R'\(E'*b),1) ;
%
% See also SPQR, SPQR_SOLVE, QR, MTIMES
% SPQR, Copyright (c) 2008-2022, Timothy A Davis. All Rights Reserved.
% SPDX-License-Identifier: GPL-2.0+
help spqr_qmult
error ('spqr_qmult mexFunction not found') ;
|
