function[y,n] = sigmult(x1,n1,x2,n2)
% implements y(n) = x1(n) * x2(n)
n = min(min(n1),min(n2)):max(max(n1),max(n2));
y1 = zeros(1,length(n));
y2 = y1;
y1(find((n >= min(n1))&(n <= max(n1)) ==1)) = x1;
y2(find((n >= min(n2))&(n <= max(n2)) ==1)) = x2;
y = y1.*y2;