# 4D matrix multiplication

4 views (last 30 days)
Kamran on 15 Oct 2021
Commented: Kamran on 20 Oct 2021
I do the following in 4 loops and it takes ages to complete. Is there a way this code could be made more efficeint, without using parallel processing toolbox?
'steer' is a 136x101x101x16 matrix
'R' is a 136x16x16 matrix
'pow' and 'F' are 101x101 matrices.
pow = zeros(grdpts_y, grdpts_x); %grdpts_y, grdpts_x = 101
for l=1:nf %nf = 136
F = zeros(grdpts_y,grdpts_x);
for i=1:grdpts_x
for j=1:grdpts_y
F(i,j) = F(i,j) + 1./(squeeze(steer(l,i,j,:))'*squeeze(R(l,:,:))*squeeze(steer(l,i,j,:)));
end
end
F = F.*conj(F);
pow = pow + F;
end
Kamran

Matt J on 15 Oct 2021
Edited: Matt J on 18 Oct 2021
steer=reshape( permute(steer,[2,3,4,1]),101^2,[],136 );
R=permute(R,[2,3,1]);
F=1./sum( pagemtimes(conj(steer),R).*steer, 2);
F=reshape( abs(F).^2 ,101,101,[]);
pow=sum(F,3);
Kamran on 20 Oct 2021
Thank you very much. You are of course right. Thanks again for the prompt help.

R2019b

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