KaTeXで使う行列の略記command

\def\mat#1{\begin{pmatrix}#1\end{pmatrix}}

e.g.

$ \def\mat#1{\begin{pmatrix}#1\end{pmatrix}} \mat{1&2&3}\mat{1\\2\\3}\mat{1&2&3\\4&5&6\\7&8&9}