Comment by knappa
I'm a mathematician. It's kind of a strange statement since, if we are talking about a matrix, it has two indices not one. Even if we do flatten the matrix to a vector, rows then columns are an almost universal ordering of those two indices and the natural lexicographic ordering would stride down the rows.
Yes. I think what all mathematicians can agree on is that the layout (and the starting index! :-) is like this: