iszero.m

来自「多小波分析源码」· M 代码 · 共 35 行

function yesno = iszero(S)

% ISZERO -- checks whether a symbolic matrix contains only zeros
%
%        yesno = iszero(S)
%
% If the symbolic matrix S contains only entries which can be
% converted to numbers, and all of them are zero (within tolerance),
% this routine returns yesno=1, otherwise yesno=0.
%
% If the matrix contains symbolic variables even after simplification,
% it is classified as nonzero, even though that may be wrong. It is
% conceivable that one of the entries is a complicated expression which is
% 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.
S = simplify(S(:));
try 
    S = double(S);
    yesno = iszero(S);
catch
% If S contains symbolic variables without numerical values,
% the conversion to "double" will fail. Then we end up here.
    yesno = 0;
end