Vectorized nD diag loop

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Javier Fernandez
Javier Fernandez 2022-7-5
评论： Javier Fernandez 2022-7-5
Hello everyone,
I have the following loop which I would want to have vectorized.
I know the diag() command cannot be used in nD arrays (n>2), so is there an alternative way to vectorize the loop?
n = 10; m = 15;
A = rand(4,n,m);
for i = 1:n
for j = 1:m
B(:,:,i,j) = diag(A(:,i,j));
end
end
Thanks in advance!

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采纳的回答

Chunru
Chunru 2022-7-5
Ran in:
n = 400; m = 500;
A = rand(4,n,m);
B = zeros(4,4,n,m); % initialize to speed up
tic
for i = 1:n
for j = 1:m
B(:,:,i,j) = diag(A(:,i,j));
end
end
toc
Elapsed time is 0.351235 seconds.
% Vectorized
tic
C = zeros(4*4,n*m);
C(1:5:16, :) = A(1:4, :);
C =reshape(C, [4, 4, n, m]);
toc
Elapsed time is 0.015569 seconds.
isequal(B, C)
ans = logical
1
  1 个评论
Javier Fernandez
Javier Fernandez 2022-7-5
This is what I was looking for! Thank you very much for your kind help.

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