# Multiple Alignments in Multlined Environment

I'm trying to get something like the second Figure; however, the best thing I got is like Figure 1. How can I fix it?

Here is the code:

\documentclass{article}
\usepackage{amsmath}
\begin{subequations}
\begin{alignat}{2}
&\begin{multlined}[b]
\{e\}^{n+1} - \{e\}^n = \Delta t \{\dot{e}\}^{n}
+ \beta \Delta t^2 \{\ddot{e}\}^{n+1} \\
+ \Delta t^2 \left( \dfrac{1}{2}-\beta \right) \{\ddot{e}\}^{n}
\end{multlined}\\
&\dfrac{1}{\Delta t} \left( \{\dot{e}\}^{n+1}  -  \{\dot{e}\}^{n} \right)=\dfrac{1}{2} \left( \{\ddot{e}\}^{n+1}  +  \{\ddot{e}\}^{n}  \right)
\end{alignat}
\end{subequations}

\end{document} • Welcome to TeX.SX! I can see no reason for the second type of alignment: there's no relationship between the plus and the minus. – egreg Apr 10 '18 at 8:57
• Thanks! This is just a simple example of the problem I've faced. I didn't bring the original equation, as it is pretty long. – Mat123 Apr 10 '18 at 9:00

Embed a \tabbedShortstack inside a \Shortstack.

\documentclass{article}
\usepackage{amsmath,tabstackengine}
\TABstackMath
\stackMath
\setstackgap{S}{6pt}
\begin{document}
\begin{equation}
\TABbinary
\Shortstack[l]{
\{e\}^{n+1} - \{e\}^n = \Delta t \{\dot{e}\}^{n}
+ \beta \Delta t^2 \{\ddot{e}\}^{n+1} \\
\tabbedShortstack[l]{
&+ \Delta t^2 \left( \dfrac{1}{2}-\beta \right) \{\ddot{e}\}^{n}\\
\dfrac{1}{\Delta t} \bigl( \{\dot{e}\}^{n+1}  &-  \{\dot{e}\}^{n} \bigr)=
\dfrac{1}{2} \left( \{\ddot{e}\}^{n+1}  +  \{\ddot{e}\}^{n}  \right) }}
\end{equation}
\end{document} I would use an align environment, with a \omit\rlap{...} for the first line.

To have the equation number only at the end, I've used \nonumber for the first two rows.

\documentclass{article}
\usepackage{amsmath}
\usepackage{array}
\begin{document}
\begin{align}
\omit\rlap{$\{e\}^{n+1} - \{e\}^n = \Delta t \{\dot{e}\}^{n} + \beta \Delta t^2 \{\ddot{e}\}^{n+1}$}\nonumber\\
&{}+\Delta t^2 \left( \dfrac{1}{2}-\beta \right) \{\ddot{e}\}^{n} \nonumber\\
\dfrac{1}{\Delta t} \left( \{\dot{e}\}^{n+1}\right. & {}-  \left.\{\dot{e}\}^{n} \right)=\dfrac{1}{2} \left( \{\ddot{e}\}^{n+1}  +  \{\ddot{e}\}^{n}  \right)
\end{align}
\end{document} 