Enumerating the List of `nPr` (n Permute r) objects
This is more of a MATLAB specific answer


  arrayfun(perms,nchoosek(A,r))


*Think of this as conceptual answer, because I have have been away from MATLAB and can't test it right now.

In other words,


get unordered combinations of elements in A, taken r at a time. using nchoosek.
get ordered combinations (with perms) of each unordered combinations. Applying a function to each element of a list can be done via arrayfun.