n=[-50:1:50];
m=n;
x=sin(0.125*pi*n);
subplot(2,1,1);
stem(n,x)
title('x');
y=0;
mn1=min(n);
mn2=max(n);
m1=4*fix(mn1/4);
m2=4*fix(mn2/4);
for n=m1:4:m2
    y=y+x.*impseq(n,-50,50);
end
subplot(2,1,2);
stem(m,y)
title('y');