Extract diagonal element from each frontal slice of tensor

Question

I have a p-by-p-by-n tensor. I want to extract diagonal element for each p-by-p slice. Are there anyone know how to do this without looping?

Thank you.

Answer 1

Just reading Divakar's answer and trying to understand why he again is roughly 10 times faster than my idea I put together code mixing both, and ended up with code which is faster:

A=reshape(A,[],n);
diags2 = A(1:p+1:p*p,:);

For a 500x500x500 tensor I get 0.008s for Divakar's solution and 0.005s for my solution using Matlab 2013a. Probably plain indexing is the only way to beat bsxfun.