# Paretheses should match same height on single line in multiple arrays

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?

-

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

One should also consider the pmatrix environment provided by amsmath, which gives better spacing for the big parentheses. – egreg May 4 '12 at 12:27