n=[-10:30];
x1=n.*(stepseq(-10,-10,30)-stepseq(20,-10,30));
x2=(cos(0.1*pi*n)).*(stepseq(0,-10,30)-stepseq(30,-10,30));
x3=((1.2).^n).*(stepseq(-5,-10,30)-stepseq(10,-10,30));
[y11,ny11]=conv_m(x1,n,x2,n);
[y12,ny12]=conv_m(x2,n,x1,n);
if ([y11,ny11]-[y12,ny12]==0)
disp('交换律成立')
end