Date: Feb 5, 2013 1:16 PM
Author: Steven Lord
Subject: Re: vectorization loops
"Christian " <email@example.com> wrote in message
> does there exist something like an approach for vectorization loops (2, 3
> or 4 nested loops)?
Be more specific, please. There are many different techniques you can use to
write MATLAB code; loops and vectorization are two such techniques.
> I mean using ndgrid, reshape, repmat, sub2ind, ... or whatever.
> I already have read a lot here in the newsgroup and the MATLAB help. Bruno
> show some very good examples here :) but mostly without some explanation.
> So I still encounter difficulties.
> Example for discussion:
> for i=1:n
> for j=1:n
> b = b + a(i,j)*a(j,i); % command
So you want to take each element of a, multiply it by its reflection in the
main diagonal, and add up all the resulting values?
eachTerm = a.*a.';
b = sum(eachTerm(:));
The first line performs all the operations a(i, j)*a(j, i) at once using
elementwise multiplication and the nonconjugate transpose (in case a
contains some complex values in your real problem, of which this is a
simplified example.) The second line performs the summation.
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