FOR loops optimisation for runtime

Is there a way to optimise this code? It takes a long time to run.

It basically comprises of 3 FOR loops running like this:

A=linspace(0,1,100);
B=linspace(0,1,100);
C=linspace(0,1,100);

zmatrix=zeros(length(A),length(B))

for i=1:length(A)
for j=1:length(B)

for k=1:length(C)
Z=A(i)+B(j)-C(k)
if Z>0
Z=zmatrix(i,j)
end
end

end
end

[Matt J]

Z=A(i)+B(j)-C(k)

Shouldn't this be

 Z(i,j,k) = A(i)+B(j)-C(k)

[James]

I just have it as Z in my code. I missed out a bit at the start where I create a zeros matrix of size (length A,length B) and then the Z values get put into that matrix in their relevant places. So had no need for it being Z(i,j,k).

[Matt J]

Rewrite your code showing how each matrix element (i,j) is calculated. If the matrix is only 100x100 it is not clear why you are looping over 100^3 combinations of i,j,k.

Answer 1

[Matt J]

This might be what you want, depending on your response to my Comment above.

 A=A(:);
 B=B(:).';
 C=reshape(C,1,1,[]);

 Z=bsxfun(@plus,A(:),B(:).');
 Z=bsxfun(@minus,Z,C);