MATLAB: How can i make the code run faster

for loopmatlab function

Hi.
Is there a better way of writing a nested loop? My code Works well but it takes about 7min to completely execute.
for i=1:Z
    n = 0;
    for j=1:N
        for k=1:M      
            if (Distance_Unique(i)==Distance(j,k))               
                n = n+1;
                Residual_Sqrd(n) = Residual_Squared(j,k);
                Summation_Residual_Squared(i) = sum(Residual_Sqrd);
            end
        end
    end
    Residual_Sqrd = zeros();
end
Thanks in advance. Darl.

Best Answer

Assuming Distance_Unique, Distance, etc. are all matrices or vectors and not functions, the two inner loops are certainly not required. I also assumed you've predeclared your Summation_Residual_Squared vector to avoid growing it in the loop.
Summation_Residual_Squared = zeros(size(Distance_Unique));
for duidx = 1:numel(Distance_Unique)
   Residual_Sqrd = Residual_Squared(Distance_Unique(duidx) == Distance);
   Summation_Residual_Squared(duidx) = sum(Residual_Sqrd(:));
end
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