Vector of Vectors possible?

General
1

Looking at some stan code from a package, I see a data format that appears to violate the rules:

vector[n] x[t];

Is this some kind of “vector of vectors”? (My understanding was that vectors are single columns) Or, is this some kind of awkward matrix?

Thanks in advance!

2

This is an older way of writing array[t] vector[n] x;. Hopefully the newer syntax makes it more clear what this is: an array of t vectors, each with length n.

This is not quite equivalent to a matrix, since it will be laid out differently in memory. Some details are described in the User’s Guide

3

Ahh, that makes sense.

Thank You!!!