Question

Okay, suppose I have a 3D matrix A and another 3D matrix Inds. What I would like to do is, for each stack A(i,j,:), permute that stack according to the indices given in Inds(i,j,:). Thus, if A(i,j,:) is [1.5 2.5 3.5] and Inds(i,j,:) is [3 2 1] then A(i,j,:) becomes [3.5 2.5 1.5].

Yes, I know A(i,j,:) is not a vector in Octave. Consider it shorthand for permute(A, [1 3 2])(i,:,j).

This should be simple, but for whatever reason I can’t seem to find the function to do it.

Answer 1

It matlab its quite simple:

A(i,j,:) = A(i,j,Inds(i,j,:));

In Matlab you can rearrange any vector using a vector of indices:

A = [10 20 30 40 50 60];
B = [6 5 4 1 2 3];
A = A(B);

A is now [60 50 40 10 20 30]

If A is MxNxP, when you use A(i,j,:) notation you are essentially dealing with a Px1 vector that you can manipulate at will.