A[:, 1] is an array of 6 reals (the first elements of each of the 6 vectors).

A[1, :] (or just A[1] for short) would be a vector of length 5 (the first of the 6 vectors of length 5).

Since 0 is just a scalar of type real this results in a real array, not an array of vectors. If you put something declared as type vector into rep_array you can get an array of vectors. More details here: