How to compute fast?

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

[Bob Thompson]

By 'vectorize' are you asking for us to help you remove one or more of the loops, or are you asking to help you multiply your large arrays together within the loops?

[Mohammod Minhajur Rahman]

Hi Bob, I just want it to compute faster. Possibly by eliminating for loops. Sorry for the confusion.

[Bob Thompson]

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]

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

Answer 1

[Jos (10584)]

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

• do not use the function CD as avariable name ...