```Date: Feb 5, 2013 1:16 PM
Author: Steven Lord
Subject: Re: vectorization loops

"Christian " <muell.halde@iwu.fraunhofer.de> wrote in message news:kereqq\$rnb\$1@newscl01ah.mathworks.com...> Hello,> 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:>> n=3;> a=rand(n,n);> for i=1:n>    for j=1:n>        b = b + a(i,j)*a(j,i);    % command>    end> end> bSo 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.-- Steve Lordslord@mathworks.comTo contact Technical Support use the Contact Us link on http://www.mathworks.com
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