How to center mathematical expression inside multi-line closed brackets? - tex

Question

How could I center the two lines inside the brackets. The code so far is:
\documentclass[a4paper,12pt,oneside]{report}
\usepackage{amsmath}
\begin{equation}
x_{t}^{\ast }(n)=
\left\{\!\begin{aligned}
& \hfil {x_{t}}\\
\hfil & {0,\text{ otherwise}}
\end{aligned}\right\}
\end{equation}

Answer 1

Here are a couple of options:
\documentclass{article}
\usepackage{amsmath,eqparbox,xparse}
% https://tex.stackexchange.com/a/34412/5764
\makeatletter
\NewDocumentCommand{\eqmathbox}{o O{c} m}{%
\IfValueTF{#1}
{\def\eqmathbox###1##2{\eqmakebox[#1][#2]{$##1##2$}}}
{\def\eqmathbox###1##2{\eqmakebox{$##1##2$}}}
\mathpalette\eqmathbox#{#3}
}
\makeatother
\begin{document}
\[
\renewcommand{\arraystretch}{1.2}
x_t^* (n) =
\left\{\begin{array}{#{} c #{}}
x_t \\
0, \text{ otherwise}
\end{array}\right\}
\]
\[
x_t^* (n) =
\left\{\begin{aligned}
\eqmathbox[cond]{x_t} \\
\eqmathbox[cond]{0, \text{ otherwise}}
\end{aligned}\right\}
\]
\end{document}
The first uses an array with a single, centred column. The second uses aligned and sets each entry inside an \eqmathbox[<tag>] with the same <tag>. eqparbox then finds the maximum width of those elements with the same <tag>, and sets each element inside a box of that width (default <align>ment is centred \eqmathbox[<tag>][<align>]{<stuff>}).