# [Tex/LaTex] Tagging multi line equations

alignequationslabels

Often I have a chain of equations but later on I only want to refer that the first statement is equal to the last one. There are some options to do that:

\begin{align}
\label{equation}
a
&=  b \\
&=  c \\
&=  d \\
&=  e \\
&=  f
\end{align}
Equation~\eqref{equation} gives $a=f$.

\begin{align}
a    \label{equation_first}
&=  b \\
&=  c \\
&=  d \\
&=  e \\
&=  f    \label{equation_last}
\end{align}
Equation~\eqref{equation_first}--\eqref{equation_last} gives $a=f$.

\begin{align*}
a
&=  b \\
&=  c \\
&=  d \\
&=  e \\
&=  f    \numberthis \label{equation2}
\end{align*}
Equation~\eqref{equation2} gives $a=f$.

$$\label{equation_split} \begin{split} a &= b \\ &= c \\ &= d \\ &= e \\ &= f \end{split}$$
Equation~\eqref{equation_split} gives $a=f$.


• The first one is just bad, as (2)–(5) are displayed, but not included in the reference.
• The second one is more or less okay, but after all it is one equation while it looks like I need six equations.
• The third one is a hack I found here (alternativly I could have used align* and lots of nonumbers). This version is okay, but does not look that good. Sure, I could put the tag on the center line, but thatâ€˜s manual work (I have to (not forget to) redo that stuff after adding some lines) and there is not always a center line.
• The fourth option looks quite good. However, I pretty much always used align[*] up to now. Are there any problems with equation+split?

How do you tag multi line equations? Why?

You could use the aligned environment:

\documentclass[10pt]{article}
\usepackage{amsmath}
\usepackage{hyperref}
\begin{document}
\begin{aligned} a &= b\\ &= c\\ &= d\\ &= e\\ &= f \label{eq:EqAligned} \end{aligned}
Equation \ref{eq:EqAligned}...
\end{document}


It centers the number vertically even if the number of equations is even, and the reference works fine.