issingular.m

几个关于多小波的程序

function yesno = issingular(S)

% ISSINGULAR -- checks whether a symbolic matrix is singular
%
%        yesno = issingular(S)
%
% We test for singularity by testing whether the determinant 
% is zero or not.
%
% If S contains only symbolic constants (not symbolic variables), 
% we do this numerically (within tolerance).
%
% If S contains symbolic variables, we do it symbolically.
% If this routine reports that such an S is singular, that will be correct.
% However, if Matlab is not able to simplify the determinant sufficiently, 
% A singular S may be incorrectly reported as nonsingular.

% Copyright (c) 2004 by Fritz Keinert ([e-mail]),
% Dept. of Mathematics, Iowa State University, Ames, IA 50011.
% This software may be freely used and distributed for non-commercial
% purposes, provided this copyright statement is preserved, and
% appropriate credit for its use is given.
%
% Last update: Feb 20, 2004

% check that S is square and two-dimensional
[n1,n2,n3] = size(S);
if (n1 ~= n2 | n3 > 1)
    yesno = 1;
    return
end

% try to simplify first
n = size(S);
S = reshape(simplify(S(:)),n);
try 
    S = double(S);
    yesno = iszero(det(S));
catch
% if S contains symbolic variables without numerical values,
% the conversion to "double" will fail. Then we end up here.
% We do the same thing, except this time the determinant
% is symbolic
    yesno = iszero(simplify(det(S)));
end