How can I implement these for loops efficiently using covolution?

2023 8 1
2 个回答
回答已采纳
更新时间：2023 8 25
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0 个投票

I have this code
for xx=1:length(x)
for kk=1:length(x)
xSinc(xx) = xSinc(xx)+x(kk)*sinc(xx-kk-delta/T);
end
end
How can implement this efficiently using convultion in MATLAB?

1 个评论
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Torsten
Torsten 2023-8-1
If you don't know how to spell the method, you'd better stick to your loop solution.

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 采纳的回答

Dyuman Joshi
Dyuman Joshi 2023-8-1
编辑：Dyuman Joshi 2023-8-1

0 个投票

Simple multiplication would be good enough -
xx = 1:length(x);
kk = 1:length(x);
xSinc(xx) = xSinc(xx) + x(kk)*sinc(xx-kk'-delta/T);

5 个评论
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MAWE
MAWE 2023-8-18
What if kk has other dimension that xx. How can I implement it?
Dyuman Joshi
Dyuman Joshi 2023-8-18
The above code will work for that as well.
MAWE
MAWE 2023-8-22
It gives me an error saying matrix dimensions must agree
Dyuman Joshi
Dyuman Joshi 2023-8-22
Please attach your code, so that I can reproduce the error and suggest solutions to tackle the issue.
MAWE
MAWE 2023-8-23
OK, it is working. I just needed to transpose one vector. Here another problem I have, the second vector depends on the first as
for xx = 1:length(x)
for kk=max(xx-L,1):min(xx+L,length(x))
xSinc(xx) = xSinc(xx)+x(kk)*sinc(xx-kk-delta/T);
end
end
Currently I am doing this
for xx = 1:length(x)
kk=max(xx-L,1):min(xx+L,length(x))
xSinc(xx) = xSinc(xx)+x(kk)*sinc(xx-kk'-delta/T);
end
Is it possible to write this for loop in vector form for efficient implementtaion?

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更多回答（1 个）

Bruno Luong
Bruno Luong 2023-8-23
编辑：Bruno Luong 2023-8-25
Ran in:

1 个投票

Ran in:
Use conv
x = (0:0.2:5).^2;
L = 3;
delta = rand; T = rand;
% Your method
xSinc = zeros(size(x));
for xx = 1:length(x)
for kk=max(xx-L,1):min(xx+L,length(x))
xSinc(xx) = xSinc(xx)+x(kk)*sinc(xx-kk-delta/T);
end
end
xSinc
xSinc = 1×26
-0.0051 -0.0070 0.0352 0.1578 0.3593 0.6413 1.0038 1.4468 1.9704 2.5745 3.2591 4.0243 4.8700 5.7962 6.8029 7.8902 9.0580 10.3063 11.6351 13.0445 14.5344 16.1048 17.7558 20.0963 21.1378 24.2622
% conv method
xSinc2 = conv(x, sinc((L:-1:-L)+delta/T), 'same')
xSinc2 = 1×26
-0.0051 -0.0070 0.0352 0.1578 0.3593 0.6413 1.0038 1.4468 1.9704 2.5745 3.2591 4.0243 4.8700 5.7962 6.8029 7.8902 9.0580 10.3063 11.6351 13.0445 14.5344 16.1048 17.7558 20.0963 21.1378 24.2622
norm(xSinc2-xSinc)
ans = 5.7220e-15
plot(xSinc, 'b')
hold on;
plot(xSinc2, 'r.')

3 个评论
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MAWE
MAWE 2023-8-23
That's an interesting approach, and it's much faster. Thank you!
MAWE
MAWE 2023-8-23
Can I ask about the undelying logic you used? Why for exampled you defined
kk = -L:L;
and then fliped the order in
K = flip(sinc(kk+delta/T));
Bruno Luong
Bruno Luong 2023-8-23
编辑：Bruno Luong 2023-8-25
I can't explain more than it comes from definition of conv adapted to your code.
Have you tried to do some study of the code or you just ask without study conv?

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