I need to do this without for loop(For Gpu computing)

I have these two problems in gpu computing in matlab

Suppose X=600*103*36 array

for n=1:36

[Q(:,:,n),R(:,:,n)]=qr(X(:,:,n));

end

I want to access all the pages at once for gpu computing. Is there a way to do ?

Problem 2:

From the above result,

suppose w is 600*36 matrix

for n=1:36

R1(:,:,n)=transpose(Q(:,:,n) )* w(600,n);

end

I wanted to make this loop without for loop for gpu computing.

Arrays here such as w, X are gpu arrays.

[Walter Roberson]

See https://www.mathworks.com/matlabcentral/answers/389566-is-there-a-way-to-run-this-loop-in-gpu-and-will-it-consume-lesser-time-compared-to-parallel-cpu-comp

[Srinidhi Ganeshan]

Mr. Walter Roberson, ThankYou for your reply :). But, in the link provided, I have to access Q values page by Page. But I wanted to access it in a stretch without for-loop for GPU Computing. I tried using reshape, pagefun, permute but till now I could not find a solution to do that without for loop.

Answer 1

[Joss Knight]

You can't do this, but I will take it as a further request for pagefun to support qr which will be coming in a future version of MATLAB.

The closest you can get is to form the block-diagonal matrix with your pages of X and solve qr for that. The results will be the equivalent block-diagonal elements of the output. Because your matrices are non-square, you would have to pad the columns with zeros.

function [Q,R] = pagefunQR(X)
    m = size(X,1);
    n = size(X,2);
    p = size(X,3);
    maxmn = max(m,n);
    A = zeros(maxmn*p,'like',X);
    for i = 1:p
        strt = (i-1)*maxmn+1;
        A(strt:strt+m-1,strt:strt+n-1) = X(:,:,i);
    end
    [Q, R] = qr(A);
    for i = 1:p
        strt = (i-1)*maxmn+1;
        Q(1:maxmn,strt:strt+maxmn-1) = Q(strt:strt+maxmn-1,strt:strt+maxmn-1);
        R(1:maxmn,strt:strt+maxmn-1) = R(strt:strt+maxmn-1,strt:strt+maxmn-1);
    end
    Q = reshape(Q(1:maxmn,:), maxmn, maxmn, p);
    R = reshape(R(1:maxmn,:), maxmn, maxmn, p);
    R = R(1:m,1:n,:);
end

Sadly, this approach is slower than just looping like you are doing. Plus it creates a huge pressure on memory.

[Srinidhi Ganeshan]

Thank you for your answer. But as you said, this is slower approach.