vectorize without using loop

I believe there's way to vectorize the following code without using the loop

                  for i = 1:length(indtrn)
                          Xtrn(i, :) = X(indtrn(i), indtrn);
                  end

Can someone shed me some light? Thanks in advance.

Answer 1

[Azzi Abdelmalek]

out=X(indtrn,indtrn)

[Eric]

exactly. Thank you, Azzi.