MATLAB: Replacing for loops with matrix math.

Question

How can I simplify this code. I.e remove the loops and replace them with matrix math.

for i=1:3
    for j = i:num_pts - i 
    diag(i,j) = testm1(j,2) * testm2(j+i,2);
    end
end

Answer 1

I wouldn't say that replacing the loops with matrix operations is a way to "simplify" it, but here's how you could do it.

[m,n]=size(diag);
[I,J]=ndgrid(1:m,1:n);
keep= J>=I & J<=num_pts-I;
I=I(keep); J=J(keep);
diag(keep) = testm1(J,2) .* testm2(J+I,2);