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Advice on a few bottlenecks in my code

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Matlab2010
Matlab2010 on 21 Feb 2013
Closed: MATLAB Answer Bot on 20 Aug 2021
According to the profiler, I have four lines of code taking up 99% of my CPU time.
if(statment)
pCond = (bold_Phi(k,2) <= data(thisIdx : idx, 7));
else
pCond = (data(thisIdx : idx, 7) <= bold_Phi(k,2));
end
IDY = find( (data(thisIdx : idx, 1) == -1) & (pCond) & (data(thisIdx : idx, 11) == bold_Phi(k,p + 10)) );
IDZ = find( (dV(thisIdx : idx, :) <= -bold_Phi(k,3)) & (pCond) & (sCond) );
where bold_Phi and data are 2D matrices and dV is a vector.
I dont think the time penalty is coming from the indexing as the following statement is very quick
~isnan(data(thisIdx : idx, 3));
anything obvious I have missed that will help me speed up these few statements?
thank you
  4 Comments

Answers (2)

Kye Taylor
Kye Taylor on 21 Feb 2013
If you don't need the actual indices, you can omit the find command to save time. In particular, notice that the following code blocks are equivalent but the first does not use find:
data = rand(1000,1);
isBig = data>0.5;
bigData = data(isBig);
and
data = rand(1000,1);
isBigIdx = find(data>0.5);
bigData2 = data(isBigIdx);
  1 Comment
Matlab2010
Matlab2010 on 22 Feb 2013
this has helped, but only a little bit. Sped up by c. 10%.

Mark Whirdy
Mark Whirdy on 22 Feb 2013
Edited: Mark Whirdy on 22 Feb 2013
(Almost-) Never use the find() function!
I'd need to see the contents of the variables, but at first glance you can maybe just remove it altogether with same functionality?

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