Paretheses should match same height on single line in multiple arrays

Question

Given is following formula:

\[
a^{(k)}=\left(\begin{array}{c}
a_1^{(k)}\\
\vdots\\
a_n^{(k)}
\end{array}\right)\to\left(\begin{array}{c}
a_1\\
\vdots\\
a_n
\end{array}\right)=a
\]

The first vector is a little bit more height than the second one. Is it possible to have the same height for all four parentheses?

Answer 1

You could use phantom (invisible) superscripts in the second array to make everything line up nicely.

\documentclass{article}
\begin{document}
\[
a^{(k)}=\left(\begin{array}{c}
a_1^{(k)}\\
\vdots\\
a_n^{(k)}
\end{array}\right)\to\left(\begin{array}{c}
a_1^{\vphantom{(k)}}\\
\vdots\\
a_n^{\vphantom{(k)}}
\end{array}\right)=a
\]
\end{document}