function[y,n] = sigadd(x1,n1,x2,n2)
%信號加y(n) = x1(n) + x2(n)

n = [min(min(n1),min(n2)):0.01*pi:max(max(n1),max(n2))];
y1 = zeros(1,length(n));
y2 = zeros(1,length(n));

leng(find(n==nin(n2))
y1(find((n >= min(n1))&(n <= max(n1)))) = x1;
y2(find((n >= min(n2))&(n <= max(n2)))) = x2;
y = y1 + y2;