The size(M) function returns an array with the number of rows as the first entry, and the number of columns as the second entry.

When M is a row-vector, the result of size(M) will have a 1 in the entry specifying the number of rows.  Similarly when M is a column-vector, there will be a 1 in the second entry of the result.

When M has more than 2 dimensions, the number of entries in M will correspond to the number of dimensions of M.

When n is given, size(M,n) will return only the number corresponding to that dimension.  size(M,1) will give the number of rows and size(M,2) will give the number of columns.

When n is larger than the number of dimensions of M, 1 will be returned.

$\mathrm{with}\left(\mathrm{MTM}\right)\:$

$\mathrm{size}\left(\mathrm{Matrix}\left(2\,3\right)\right)$

$\left[\begin{array}{cc}2& 3\end{array}\right]$

$\mathrm{size}\left(\mathrm{Matrix}\left(2\,3\right)\,2\right)$

$3$