function y=myconv(x1,x2)
x1=[1,-1,1,2];
x2=[1,1,2];
N1=length(x1);
M=length(x2);
L=N1+M-1;
for(n=1:L)
y(n)=0;
for(m=1:M)
k=n-m+1;
if(k>=1&k<=N1)
y(n)=y(n)+x2(m)*x1(k);
end
end
end
y1=conv(x1,x2);
nx1=-1:2;
nx2=0:2;
ny=-1:4;
subplot(3,1,1);stem(nx1,x1)
xlabel('n');ylabel('x1(n)')
axis([-2,5,-2,2])
set(gca,'XTickMode','manual','XTick',[-2:1:5])
grid on;
title('序列 x1')