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How can speed up the blow codes?

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Amir Torabi
Amir Torabi on 2 Dec 2019
Edited: Fabio Freschi on 3 Dec 2019
The blow code is part of my project. the performance of this code is alittle low. it is about 0,5s but in higher Nx values, the effiency decreases. Also, etas is a (Nx*Ny,ngrain=70) matrix. it does not contain zero values. I'd be appreciate if any suggest can improve the efficiency of below code.
Nx=512;
for igrain=1:70+0
ncount=0;
for i=1:Nx
for j=1:Nx
ii =(i-1)*Nx+j;
eta2(i,j) =eta2(i,j)+etas(ii,igrain)^2;
if(etas(ii,igrain) >= 0.5)
ncount=ncount+1;
end
ncount=ncount/(512*512);
end
end
  1 Comment
Nicolas B.
Nicolas B. on 2 Dec 2019
are eta2 and etas pre-defined tables? Or are the size of these variables change?

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Answers (1)

Fabio Freschi
Fabio Freschi on 2 Dec 2019
Edited: Fabio Freschi on 2 Dec 2019
Edit: added attempt for ncount
I don't understand what ncount is doing, it looks like a counter but I don't understand why you are repeatedly dividing by 512*512. I made my try, but some insight could help. However the calculation of eta2 can be drastically simplified using vectorization. Here I compare your solution (with some fixes) with the vectorized version (with a '0' added o the variables' names)
Nx = 512;
ngrain = 70;
eta2 = zeros(Nx,Nx);
etas = rand(Nx*Nx,ngrain);
ncountTot = zeros(ngrain,1);
% original code (with some fixes)
tic
for igrain=1:ngrain
ncount=0;
for i=1:Nx
for j=1:Nx
ii =(i-1)*Nx+j;
eta2(i,j) =eta2(i,j)+etas(ii,igrain)^2;
if(etas(ii,igrain) >= 0.5)
ncount=ncount+1;
end
end
ncountTot(igrain)=ncount/(Nx*Nx);
end
end
toc
% vectorized code
tic
etas0 = reshape(etas,Nx,Nx,ngrain);
eta20 = sum(etas0.^2,3)';
ncountTot0 = squeeze(sum(etas0 >= 0.5,[1 2])/(Nx*Nx));
toc
% check
norm(eta2-eta20)/norm(eta2)
norm(ncountTot-ncountTot0)
  2 Comments
Fabio Freschi
Fabio Freschi on 3 Dec 2019
My pleasure! If the answer solves your original problem, please accept it.
For the second code, could you please check it? it looks like one for loop is missing
Do you need at the end of the loop only term3 or also den?

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