How to compute fast?

Question

Mohammod Minhajur Rahman 2019-2-28

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/447564-how-to-compute-fast

评论： Mohammod Minhajur Rahman 2019-2-28

采纳的回答： Jos (10584)

在 MATLAB Online 中打开

Hi, I have the following code that I need to vectorize to compute faster:

Here,

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)]);
     end
end

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Bob Thompson 2019-2-28

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.

Mohammod Minhajur Rahman 2019-2-28

Hi Bob, thank you for your time. I would wait for a solution while trying by myself.

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Answer 1

Jos (10584) 2019-2-28

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/447564-how-to-compute-fast#answer_363234

编辑：Jos (10584) 2019-2-28

在 MATLAB Online 中打开

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 !!
    end
end