The horzcat(M1,M2) function creates a new array with the columns of M2 to the right of the columns of M1.

All input arrays must have the same number of rows and dimensions.

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

$\mathrm{M1}≔\mathrm{Matrix}\left(2\,3\,'\mathrm{fill}'=1\right)\:$

$\mathrm{M2}≔\mathrm{Matrix}\left(2\,2\,'\mathrm{fill}'=2\right)\:$

$\mathrm{horzcat}\left(\mathrm{M1}\,\mathrm{M2}\right)$

$\left[\begin{array}{ccccc}1& 1& 1& 2& 2\\ 1& 1& 1& 2& 2\end{array}\right]$