# Is it possible to make two tags for the same equation?

In the screenshot below, I want to add another tag, namely by (a) for the equation tagged already by (1). How can I achieve that?

Here is my code concerning this part:

\begin{align*}
\\&= 2 A\bigl( v^1,v^2,v^3,v^4 \bigr)
+ 2 A\bigl( v^1,v^4,v^3,v^2 \bigr)
+ 2 A\bigl( v^1,v^2,v^1,v^4  \bigr)   + 2 A\bigl(v^1,v^2,v^3,v^2  \bigr) \\
&\phantom{{}= }+ 2 A\bigl(v^1,v^4,v^3,v^4  \bigr) + 2 A\bigl( v^3,v^2,v^3,v^4 \bigr). \tag{1}
\end{align*}


Note: My preamble is the default one and I am using the article document class.

• Do you mean tagging it such that you obtain (1)(a)? – Troy Apr 21 '17 at 12:35
• Something like that. Precisely, by (a) then a little space and then (1) . – Hussein Eid Apr 21 '17 at 12:39
• What do you mean by default preamble? – user31729 Apr 21 '17 at 13:08
• You may give a look to this question and the questions linked there. – campa Apr 21 '17 at 13:17

It is not a tag, but a textual explanation:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\begin{align*}
x&=y
\\
&= 2 A( v^1,v^2,v^3,v^4 )
+ 2 A( v^1,v^4,v^3,v^2 )  \\
+ 2 A(v^1,v^2,v^3,v^2  ) \\
&\quad+ 2 A(v^1,v^4,v^3,v^4  ) + 2 A( v^3,v^2,v^3,v^4 ).
&&\text{by (a)} \tag{1}
\end{align*}

\end{document}


• Shouldn’t it rather be ...v^4),&&\text{by (a).}? (I mean, the punctuation.) – GuM Apr 21 '17 at 21:35
• @GustavoMezzetti Probably; I just took the OP's code. – egreg Apr 21 '17 at 21:50

This uses a single tag with two things inside. Modifying \theequation is simpler, but treats the outer parentheses differently from the inner. The last version does not include both parts in the \ref.

\documentclass{article}
\usepackage{amsmath}
\usepackage{showframe}
\usepackage{hyperref}

\newcommand{\flalignbalance}{\hphantom{(\theequation)}\hskip\mintagsep}

\begin{document}
This should link to \ref{test}, \eqref{test2} and \ref{test3}
\vfill
This uses \verb$\tag*$
$$\stepcounter{equation}\label{test} x=a \tag*{(a) (\theequation)}$$
\vfill
\bgroup
\renewcommand{\theequation}{a) (\arabic{equation}}
This reformats \verb$\theequation$.
$$\label{test2} y=b$$
\egroup
\vfill
This uses \texttt{flalign}.  \verb\flalignbalance is used to center the equation.
\begin{flalign}\label{test3}
\flalignbalance&& z&=c &\llap{(a)}
\end{flalign}
\end{document}