Trying to align the equations and labelling
In align
you use &=
, not &=&
like in eqnarray
. For the numbering, change align*
to align
and add \nonumber
to the end of the first line.
\documentclass[12pt,letterpaper]{article}
\usepackage[a4paper,left=20mm,top=25mm,right=20mm,bottom=25mm]{geometry}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}
\begin{document}
Asymptotic equation of Motion
\begin{align}
\mathcal{L}_n (\nabla_{\mu} n_{\nu}) &= n^{\alpha} \nabla_{\alpha} (
\nabla_{\mu} n_{\nu}) + \nabla_{\alpha} n_{\nu} \nabla_{\mu} n^{\alpha} +
\nabla_{\mu} n_{\alpha} \nabla_{\nu} n^{\alpha} \nonumber \\ % <---- add \nonumber here
&= n^{\alpha} \nabla_{\alpha} ( \nabla_{\mu} n_{\nu}) - n^{\alpha}
\nabla_{\mu} ( \nabla_{\alpha} n_{\nu}) + n^{\alpha} \nabla_{\mu} (
\nabla_{\alpha} n_{\nu}) + \nabla_{\alpha} n_{\nu} \nabla_{\mu} n^{\alpha} +
\nabla_{\mu} n_{\alpha} \nabla_{\nu} n^{\alpha}
\end{align}
\end{document}
For a single equation, the choice should be split
inside equation
:
\documentclass[12pt]{article}
\usepackage[a4paper,left=20mm,top=25mm,right=20mm,bottom=25mm]{geometry}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}
\begin{document}
Asymptotic equation of Motion
\begin{equation}
\begin{split}
\mathcal{L}_n (\nabla_{\mu} n_{\nu})
&= n^{\alpha} \nabla_{\alpha} ( \nabla_{\mu} n_{\nu})
+ \nabla_{\alpha} n_{\nu} \nabla_{\mu} n^{\alpha}
+ \nabla_{\mu} n_{\alpha} \nabla_{\nu} n^{\alpha}
\\
&= n^{\alpha} \nabla_{\alpha} ( \nabla_{\mu} n_{\nu})
- n^{\alpha} \nabla_{\mu} ( \nabla_{\alpha} n_{\nu})
+ n^{\alpha} \nabla_{\mu} ( \nabla_{\alpha} n_{\nu})
+ \nabla_{\alpha} n_{\nu} \nabla_{\mu} n^{\alpha}
+ \nabla_{\mu} n_{\alpha} \nabla_{\nu} n^{\alpha}
\end{split}
\end{equation}
\end{document}
If you prefer the number to be at the bottom, this should be a global decision, that can be accomplished by calling amsmath
with the tbtags
option:
\usepackage[tbtags]{amsmath}
With this single change, the output would become
Note that amsmath
alignment environments use &=
(not &=&
). I removed the letterpaper
option, that does nothing and might be a bit unclear.