difference between aligned and gathered in latex
\documentclass{article}
\usepackage[a6paper,margin=1cm,showframe]{geometry}
\usepackage{pst-node,multido}
\usepackage{amsmath}
\begin{document}
\multido{\n=0.5+0.1}{4}{%
\endgraf\noindent\pnode(.5\linewidth,0){T}
%
\begin{equation*}\!
\begin{aligned}
\framebox[\n\linewidth]{aligned \n}
\end{aligned}\tag*{Def}
\end{equation*}
%
\begin{equation*}
\begin{split}
\framebox[\n\linewidth]{split \n}
\end{split}\tag*{Def}
\end{equation*}
%
\endgraf\noindent\pnode(.5\linewidth,0){B}
\psset{linecolor=blue}
\ncline{T}{B}
\pcline[nodesep=-\dimexpr\n\linewidth/2](B)(B)}
\end{document}