MATLAB: How to vectorize a loop with multi-dimensional arrays/ outer product

for loopMATLABmulti-dimensional arraysvectorization

Hi, would someone happen to know how I could vectorize the following loop?

      L=4;
      for t=1:N;
        A(:,:,t)=exp(a*(t-1)).*B(:,:,L);
      end

many thanks, Eli

Best Answer

B1 = B(:,:,4);
out = reshape(B1(:)*(0:N-1),[size(B1) N]);

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MATLAB: For a loop , to carry out element by element multiplication is bsxfun better than conventional element by element.

Only in the circumstances that you are using R2016b or later and B has a different dimension than A, such as if A is 2d and B is a vector with the same number of rows as A has. Releases before that would return an error message in that situation, but starting R2016b MATLAB would use implicit expansion. Implicit expansion has been timed as no faster than bsxfun and typically a bit slower than bsxfun.

But in the case where the two array are the same size, bsxfun is expected to be slightly slower due to the overhead of testing to determine that regular operations can be used.

MATLAB: Fast Element-Wise power

   a=1:10000000;
  b=repmat(3,size(a));
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  toc
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  c2=a.^3;
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  tic
  c3=a.*a.*a;
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And then the results are,

 Elapsed time is 0.118509 seconds.
 Elapsed time is 0.129281 seconds.
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Best Answer

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MATLAB: For a loop , to carry out element by element multiplication is bsxfun better than conventional element by element.

MATLAB: Fast Element-Wise power

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