MATLAB Answers


How to compute fast?

Hi, I have the following code that I need to vectorize to compute faster:
neq = 3197;
length(K1) = 152;
d1 is such d1{1,i} = 3197 by 1;
delNonZero = 152 by 1;
cd = zeros(neq,neq);
for i = 1:length(K1)
for j = 1:length(K1)
cd =cd+ d1{1,i}*d1{1,j}'*mean([delNonZero(i) delNonZero(j)]);


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Hi Bob, I just want it to compute faster. Possibly by eliminating for loops. Sorry for the confusion.
Got it. I am not an expert in those things, so hopefully somebody else can offer you a better solution. I will say that I don't know if you can eliminate the loops because of your desire to look at just a few elements at a time, rather than just looking at entire rows or the like.
Hi Bob, thank you for your time. I would wait for a solution while trying by myself.

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1 Answer

Answer by Jos (10584)
on 28 Feb 2019
Edited by Jos (10584)
on 28 Feb 2019

Some suggestions:
  • replace mean(A,B) by (A+B)/2
  • you can have j run from i to length(K1), since everything seems symmetric (unless there are complex numbers involved):
for i = 1:..
cd = cd + d1{i,1}*d1{i,1}'*delNonZero(i) ;
for j = i+1: ..
cd = cd + 2*d1{i,1}*d1{j,1}'*(delNonZero(i)+delNonZero(j))/2; % you can remove the 2's !!
  • do not use the function CD as avariable name ...


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