Vertically align comma with matrices in math mode

Question

When I'm writing an equation with multiple matrices, the comma is still placed at normal text-height, which looks strange.

$\mathrm{f}\left(
\begin{bmatrix} a_1\\a_2\end{bmatrix}, 
\begin{bmatrix} b_1\\b_2\end{bmatrix}\right)$

How can I automatically align it with the bottom of the vectors so it looks natural?

Answer 1

Make the comma part of a matrix, too.

\documentclass{article}
\usepackage{amsmath}
\begin{document}
$\mathrm{f}\left(
\begin{bmatrix} a_1\\a_2\end{bmatrix}
\begin{matrix} \\,\end{matrix} 
\begin{bmatrix} b_1\\b_2\end{bmatrix}\right)$
\end{document}