How to vectorize this nested loop for optimized performance

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Yodish 2017-12-18

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https://ww2.mathworks.cn/matlabcentral/answers/373555-how-to-vectorize-this-nested-loop-for-optimized-performance

评论： Matt J 2017-12-19

hello everybody, I have been trying to optimize this nested for loop which is very very slow, but with no success

    for i=1:size(Sxx,2)-1
                for j=1:size(Sxx,2)-1
                    A=Sxx(:,i).*conj(Sxx(:,j));
                    B= (ifft(A, 'symmetric'));
                    [~, T(i,j)] = max(B(1:round(end/2)));
                end
            end

any help is appreciated!

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Answer 1

Matt J 2017-12-18

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https://ww2.mathworks.cn/matlabcentral/answers/373555-how-to-vectorize-this-nested-loop-for-optimized-performance#answer_296835

编辑：Matt J 2017-12-19

在 MATLAB Online 中打开

My advice would be not to vectorize it completely (although there are ways to do so), but rather reduce it to one loop as below.

   [m,n]=size(Sxx);
   k=1:round(m/2);
   SxxConj=conj(Sxx(:,1:n-1));
     T=nan(n-1);
      for i=1:n-1
        B=ifft(Sxx(:,i).*SxxConj, [],1,'symmetric'); %If <R2016b use bsxfun
        [~,T(i,:)]=max(B(k,:),[],1);  %EDITED
      end