isidentity.m

几个关于多小波的程序

function yesno = isidentity(S)

% ISIDENTITY -- checks whether symbolic object is the identity matrix
%
%        yesno = isidentity(S)
%
% If the symbolic matrix S contains only entries which can be
% converted to numbers, and equals an identity matrix (within tolerance),
% this routine returns yesno=1, otherwise yesno=0.
%
% If the matrix contains symbolic variables even after simplification,
% it is not recognized as the identity matrix, even though that may be wrong.
% It is conceivable that a complicated expression might simplify
% to one or zero, even though Matlab does not see how to simplify it.

% 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

% Matlab cannot handle symbolic matrices of more than two
% dimensions correctly. We need to string S out first.
n = size(S);
S = simplify(S(:));
try 
    D = reshape(double(S),n);
    yesno = isidentity(D);
catch
% if S contains symbolic variables without numerical values,
% the conversion to "double" will fail. Then we end up here.
    yesno = 0;
end