New Post: Extract multiply element from a matrix efficiently

Hi,
I was wondering is there an efficient way to extract multiply element from a matrix efficiently?

For example,
I have a index vector idx = [0, 1, 3, 5] and have a matrix rho 8x8.

How can I get a new matrix which are composed from rho matrix with idx number [0,0], [0,1], [0.3], [0,5], [1,1], [1,3], .... etc...


Thanks