I need help with convolution sum in Labview

[gaiab03]

I uploaded the wrong version, wait here it is corrected

[gaiab03]

@altenbach can you see this final VI correctly?
It's in 2019 with all the datas

[altenbach]

Yes, this works and produces output. You say that the result is not as expected. What is the expected result?

(Sorry, I need to switch to my desktop later. my laptop screen is not big enough to efficiently look at this)

[gaiab03]

I should be obtaining the same graph I obtain in MatLab (the output of waveform graph 3). The output of matlab is attached. 
You're really kind btw thank you so much for your help! 
I will probably look at your adjustments tomorrow morning (I'm in Italy), so feel free to do it when you have time 🙂

[gaiab03]

I can attach the MatLab code that works and does the convolution correctly. 

This is the code that I wrote on Matlab (and gives the correct result) and I wanted to implement on LabView:

for i=1:1:200 (200 is Mtot*2-1, I wrote it as a constant on Matlab for simplicity)

l=200;

for k=1:1:200

if i-k>0

c(i)=c(i)+a(k)*b(i-k);

else

c(i)=c(i)+a(k)*b(l);

l=l-1;

end

end

end

This is my implementation of those lines on labview. The problem must be there, as every other part works perfectly (simulation, algorithm one and all the spectrum) or maybe where I mirrored and expanded the periodic spectrum of V and I.

[altenbach]

Sorry, I no longer do text based code*. Can you save your Matlab output for the current inputs to a simple text file?

*(I did text based code from 1973 to 1996, switched to LabVIEW 4.0 and never looed back since 😄 )

[gaiab03]

The output is the graph attached in the previous message (It's in png format). 

Do you prefer another format for images? I can't turn an image into a txt. 

[Andrey_Dmitriev · Accepted solution]

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@gaiab03 wrote:

I should be obtaining the same graph I obtain in MatLab. The output of matlab is attached. 🙂

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If you need to obtain same output as from given script,

Spoiler

clear all
a=zeros(200, 1);
a(2,1)=-150i;
a(4,1)=-100i;
a(6,1)=-50i;
a(102,1)=-150i;
a(104,1)=-100i;
a(106,1)=-50i;
a(100,1)=150i;
a(98,1)=100i;
a(96,1)=50i;
a(200,1)=150i;
a(198,1)=100i;
a(196,1)=50i;
b=zeros(200, 1);
b(2,1)=-250i;
b(4,1)=-100i;
b(102,1)=-250i;
b(104,1)=-100i;
b(100,1)=250i;
b(98,1)=100i;
b(200,1)=250i;
b(198,1)=100i;
c=zeros(200, 1);
for i=1:1:200
l=200;
for k=1:1:200
if i-k>0
c(i)=c(i)+a(k)*b(i-k);
else
c(i)=c(i)+a(k)*b(l);
l=l-1;
end
end
end

 
% Plot the histogram of abs(c)
figure(1);
bar(1:200, abs(c)); % Plot the absolute values of c
xlabel('Array Indexes');
ylabel('Amplitude');
title('Histogram of abs(c)');
grid on;

then it could be like this:

The graphs are the same:

And values are identical:

Some issues may present, but hopefully the overall idea is clear more or less.

[gaiab03]

Thank you so much!
You're really helped me a lot!
The solution works also on my project

[altenbach]

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@Andrey_Dmitriev wrote:

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@gaiab03 wrote:

I should be obtaining the same graph I obtain in MatLab. The output of matlab is attached. 🙂

---

If you need to obtain same output as from given script,

.

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It is just a circular convolution and all you need is code the size of a postage stamp. The following gives the same result!

I changed the cosmetics of the graph to show both as points. Modify as desired.

Of course the lingering question is if this is really what you need. 😄