+Returns a matrix with the same dimensions as @var{m} in which each
+elements is a unique integer, from 1 to the number of elements in
+@var{m}, that corresponds to its rank within @var{m}. The smallest
+element in @var{m} corresponds to value 1 in the returned matrix, the
+next smallest to value 2, and so on. When multiple elements in
+@var{m} have the same value, they are assigned consecutive unique
+ranks in the return matrix.