Manual 2D fft

I want to do 2D FFT manually, but the result is different fro what we get from MATLAB buit in function. Here is my code I have used for 2d FFT. Can anyone figure it out where is my code running wrong?

r = zeros(40,1);
c= 2;
theta = zeros(40,1);
for i = 0:39
    r(i+1) = c*sqrt(i);
theta(i+1) = i*137.508;
end
theta = deg2rad(theta);
  xi = r.*cos(theta);
 yi = r.*sin(theta);

B = zeros(512,512);
si= 0;
 for ii = -256:255
     for j = -256:255
       for k = 1:40
         s = exp(-1i*2*pi*(ii*xi(k) +j*yi(k)));
        si = sum(s) +si;
       end
         B(ii+257,j+257) = si;
        si = 0;
     end
      
 end
 
 

[KALYAN ACHARJYA]

Can you verify with simple example? Share your manual calculation, I will try to figure out?

[ritika malik]

I want to calculate fourier transform of the image attached here. Here, I am using 21 delta function at different position calculated in above code as (xi,yi). Now the fourier transform of these delta funtion is

I want to calculate B(u,v) using this formula. Which expected to be like as the second image (energy c=2.png) I have attached, which I am not getting using above code.