Clear Filters
Clear Filters

3d Matrix - Extract Subarray and Multiply by Conjugate Transpose without Forloops

3 views (last 30 days)
I have a 3d matrix A(i,j,k) of size [1:100,1:10000,1:989]. On the kth index I want to extract the 989 elements into a vector u and form the product u*ctranspose(u), for each of the indices.
Using a double for loop, which is not something one should do in Matlab,
% this is an evil double for loop - I want to avoid doing this.
for ii=1:100
for jj=1:10000
u=squeeze(A(ii,jj,:));
% somehow compute and store uu in a vectorized way, but how?
uu=u*ctranspose(u); % note that uu is a 989x989 matrix, not a vector.
end %ii
end %jj
This would be really slow. Is there a vectorized way to the above, so I am not doing a double for loop?
  17 Comments
Science Machine
Science Machine on 8 Sep 2022
Edited: Science Machine on 8 Sep 2022
t and ras parameters are the ii and jj indices from above u of size 1:100 and 1:10000, and the vector $$ has parameters jj also.

Sign in to comment.

Accepted Answer

Matt J
Matt J on 7 Sep 2022
Edited: Matt J on 7 Sep 2022
[m,n,p]=size(A);
Ar=reshape(A,[],p).';
UU = reshape(Ar,p,1,[]).*conj(reshape(Ar,1,p,[]));
UU=reshape(UU,p,p,m,n); %obtain the (i,j)-th outer product as UU(:,:,i,j)
  3 Comments
Science Machine
Science Machine on 7 Sep 2022
How did you learn to do such things? I knew reshape function but it did not occur to me to use it here.

Sign in to comment.

More Answers (0)

Products


Release

R2022a

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!