for loops vectorization for GPU

hello people,

i want to change for loops for GPU computing.

How to effectively vectorize the loop in this code? i get stuck on this problem. help me plz :)

pnx=101;
pny=101;
pnz=101;

[pY, pX] = meshgrid(linspace(-0.5,0.5,pnx),linspace(-0.5,0.5,pny));

cnt_t=2601;
cnt_r=2601;

tr_x=linspace(-1,1,cnt_t);
tr_y=linspace(-1,1,cnt_t);
re_x=linspace(-2,2,cnt_r);
re_y=linspace(-2,2,cnt_r);

pza=linspace(0,5,101);

Obj=ones(101,101,101);
Obj(:,:,30)=Obj(:,:,30).*2;
Obj(:,:,60)=Obj(:,:,60).*3;

S= zeros(cnt_t,cnt_r);

for k = 1:cnt_t  
k
    for l = 1:cnt_r 

        S1=zeros(pnx,pny);

        for z_cnt = [30 60] 
            
            A = exp(1i*sqrt(  (tr_x(k)-pX).^2 + (tr_y(k)-pY).^2 + (pza(z_cnt)).^2 ) );
            B = exp(1i*sqrt(  (re_x(l)-pX).^2 + (re_y(l)-pY).^2 + (pza(z_cnt)).^2 ) );
            S1 = S1 + Obj(:,:,z_cnt).*A.*B; 
            
        end % for t
        
        S(k,l) = sum(sum(S1)); 
        
    end  % for l
end  % for k

Answer 1

[Ishu]

Hi Youngjin,

I understand that you want to use GPU computation in MATLAB. To use GPU computation you can convert your normal arrays into "gpuArray".

% converting normal arrays into gpuArray
[pY, pX] = gpuArray(meshgrid(linspace(-0.5,0.5,pnx),linspace(-0.5,0.5,pny)));
cnt_t=2601;
cnt_r=2601;
tr_x=gpuArray(linspace(-1,1,cnt_t));
tr_y=gpuArray(linspace(-1,1,cnt_t));
re_x=gpuArray(linspace(-2,2,cnt_r));
re_y=gpuArray(linspace(-2,2,cnt_r));
pza=gpuArray(linspace(0,5,101));

To further accelerate your computations you can also use "parfor" instead of normal "for" loop.

For more information on you can refer below documentation:

parfor : https://www.mathworks.com/help/parallel-computing/parfor.html

gpuArray: https://www.mathworks.com/help/parallel-computing/gpuarray.html

Hope it help!