find convolution of two signals

clc
close all
x=[4 6 7 9];
h=[5 2 3 11 15];
m=length(x);
n=length(h);
X=[x,zeros(1,n)];
H=[h,zeros(1,m)];
for i=1:n+m-1
Y(i)=0;
for j=1:m
if(i-j+1>0)
Y(i)=(Y(i)+x(j))*H(i-j+1);
else
end
end
end
stem(Y);