How to reduce for loops?

Hello, I am currently working on 2-Dimensional Hartley transform.The code is shown below:

clc;clear all;close all;
img =imread('101_7.tif');
figure;imshow(img);
X = zeros(size(img,1),size(img,2));

   for u=1:size(img,1)
       for v=1:size(img,2)
          for x=1:size(img,1)
              for y=1:size(img,2) 
                  a = 2*pi*u*x/size(img,1);
                  b = 2*pi*v*y/size(img,2);
                  temp= img(x,y)*(cos(a+b) + sin(a+b));
                  X(u,v)= X(u,v)+temp;
              end
          end
      end
  end

It has 4 for loops and it takes a very long time to execute this. Is there any method to make it more efficient by reducing the for loops? Anything regarding this would be very helpful.

The formula used for this 2-D Hartley transform is shown below:

Reference:Separable two-dimensional discrete Hartley transform by Andrew B. Watson and Allen Poirson.

Thank you.

[cbentter]

This work could help you: FAST ALGORITHMS OF FOURIER AND HARTLEY TRANSFORM AND THEIR IMPLEMENTATION IN MATLAB by VíTÌZSLAV VESELÝ