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Convolution Computations results for a system response.

Can anyone tell the difference of these plots that I used following two codes to plot the results of convolution computations given and need to know the reason for having following difference?
I have attached the results I got for these codes.

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1 Answer

Answer by Bruno Luong
on 16 Sep 2019
Edited by Bruno Luong
on 16 Sep 2019
 Accepted Answer

You make few mistakes, indexing and flipping (see careful conv documentation, the subtility is there, though TMW never mention whereas CEIL or FLOOR must be applied on even-length kernel, shame on them).
This code will show the correction and match both calculations (roundoff beside)
n=[1:1:1000];
s=10*cos(0.05*n);
N=randn(1,1000);
x=s+N;
h=0.1*ones(1,10);
y = conv(x,h,'same'); % 'same'
yy = zeros(1,length(n));
for i = 1: length(n)
for j = 1:length(h)
k = i-j+ceil((length(h)+1)/2); % shift by ceil(...) which correspond to "same"
if k>=1 && k<=length(x) % overflow check
yy(i) = yy(i) + h(j)*x(k);
end
end
end
close all
figure
plot(yy)
hold on
plot(y)
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