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
|
function Nexp = spqr_explicit_basis (N, type)
%SPQR_EXPLICIT_BASIS converts a null space basis to an explicit matrix
%
% Convert a orthonormal null space bases stored implicitly and created
% by spqr_basic, spqr_null, spqr_pinv, or spqr_cod to an an explicit
% sparse, or optionally full, matrix. If the input is not a implicit null
% space bases the input is returned unchanged.
%
% Examples:
% A = sparse(gallery('kahan',100));
% N = spqr_null(A); % creates an implicit null space basis
% Nexp = spqr_explicit_basis (N) ; % converts to a sparse matrix
% Nexp = spqr_explicit_basis (N,'full') ; % converts to a dense matrix
%
% Note that the dense matrix basis will require less memory than the implicit
% basis if whos_N.bytes > ( prod(size(N.X)) * 8 ) where whos_N = whos('N').
%
% See also spqr_basic, spqr_null, spqr_cod, spqr_pinv, spqr_null_mult.
% spqr_rank, Copyright (c) 2012, Leslie Foster and Timothy A Davis.
% All Rights Reserved.
% SPDX-License-Identifier: BSD-3-clause
is_implicit_basis = ...
isstruct(N) && isfield(N,'Q') && isfield(N,'X') ;
if is_implicit_basis && nargin == 1
Nexp = spqr_null_mult(N,speye(size(N.X,2)),1) ;
elseif is_implicit_basis && nargin == 2 && strcmp(type,'full')
% Nexp = spqr_null_mult(N,eye(size(N.X,2)),1) ; % slow for large nullity
Nexp = spqr_null_mult(N,speye(size(N.X,2)),1) ;
Nexp = full(Nexp) ;
else
Nexp = N ;
end
|
