Add multiple channels to a 28x28x5000 matrix

Question

I have an array of size 28x28x5000. I need to convert it to 28x28x3x5000. The third dimension represents channels. Each channel is the same copy.

How can I do this in Matlab without using a loop?

Answer 1

Another one-liner is repmat(reshape(A,[28,28,1,5000]),1,1,3,1);