how can i vectorize this loop?

 K=100;
 a=zeros(K,1);
 for u = 0:K-1
    for b = 0:K-1
    a(u+1) = a(u+1) + s(b+1)*exp((-2j*pi*u*b/K)); 
    end
 end

[Matt J]

What is "k" in s(k+1)? DO you mean s(b+1)?

[Miguel Reina]

Yes is b+1

Answer 1

[Matt J]

a=fft(s);

Answer 2

[Image Analyst]

Well you could try meshgrid() but I think it might make it a little more confusing to understand what it's doing. With only 100x100 array to fill, a double for loop will be very fast so even if you did vectorize it, don't expect to notice any speed difference.

Answer 3

[Matt J]

A less efficient way,

z=0:K;

a=exp((-2j*pi/K)*z.'*z)*s(:);