# Name a formula in align

If I have a (centered) formula/equation (in my example A+B=C) in align. How can I name this formula? I want the text to be on the right side. I know that hfill doesn't work.

\begin{align*}
A+B=C     \hfill  \text{name of the formula}
\end{align*}

\begin{itemize}
\item[$(1)$] ......
\begin{align*}
\tag{Not Centered}
A+B=C
\end{align*}
\item[$(2)$] ....
\end{itemize}

• \tag{name of the formula} – Sigur Jul 11 '14 at 1:03
• But then the formula is not correctly centered. – user144921 Jul 11 '14 at 1:07
• Using amsmath package do $A+B=C \eqno{\text{name of the formula}}$. – Sigur Jul 11 '14 at 1:21
• I don't understand what is the behavior you want if you use the itemize environment. – skpblack Jul 11 '14 at 2:39

Naming a formula is best achieved using \tag{<stuff>} (or the starred version which removes the surrounding parentheses). For centering an equation with regards to the text block when inside a list, you need to remove the left margin inserted by the list (\@totalleftmargin). Note that this margin is increased the deeper you nest lists.

Below I display the use of the latter using \displayinlistundent to insert a space to center the equation. Place this at the end of the equation:

\documentclass{article}
\usepackage{amsmath}
\makeatletter
\newcommand{\displayinlistundent}{\hspace{\@totalleftmargin}}
\makeatother
\begin{document}

\begin{align}
A + B = C
\end{align}

\begin{enumerate}
\item A regular \verb|align|:
\begin{align}
A + B = C
\end{align}

\item A centred \verb|align|:
\begin{align}
A + B = C \displayinlistundent
\end{align}

\item A nested list
\begin{enumerate}
\item A regular \verb|align|:
\begin{align}
A + B = C
\end{align}

\item A centred \verb|align|:
\begin{align}
A + B = C \displayinlistundent \tag{Very important}
\end{align}

\item A nested list
\begin{enumerate}
\item A regular \verb|align|:
\begin{align}
A + B = C \tag{My equation}
\end{align}

\makeatletter
\item A centred \verb|align|:
\begin{align}
A + B = C \displayinlistundent
\end{align}
\makeatother
\end{enumerate}
\end{enumerate}
\end{enumerate}

\end{document}


If you wish to use \tag*, you need to insert it using \tag*{\llap{<stuff>}} if you want things to remain centred:

\item A centred \verb|align|:
\begin{align}
A + B = C \displayinlistundent \tag*{\llap{Very important}}
\end{align}

• whether the left margin of display math is adjusted within lists depends on the document class. the ams classes, for example, don't adjust; they always center on the whole line. this is a publisher house style decision. – barbara beeton Jul 11 '14 at 12:24

Not very sure what you are asking. But here is a try,

\documentclass{article}
\usepackage{kantlipsum}
\usepackage{amsmath}
\begin{document}
\kant[1]
\begin{align*}
\tag{Not Centered}
y = 3x
\end{align*}
\begin{center}
\begin{align*}
\tag{Centered}
y = 3x
\end{align*}

\end{center}
\end{document}


• Thank you, this is what I needed. But why doen't work this in the case of using align in itemize? I added an example. – user144921 Jul 11 '14 at 1:33
• This don't works if the name is very large. For example \tag{This a larger name} doesn't center the formula. – skpblack Jul 11 '14 at 1:33
• Hm, I see it. That's a problem. – user144921 Jul 11 '14 at 1:35
• And it makes problems in combination with itemize... – user144921 Jul 11 '14 at 1:35

I thought of the following to resolve the problem:

• Create a new command \rtag that redefines \tag for right alignment with

\newcommand*{\rtag}[1]{\tag*{\makebox[0pt][r]{(#1)}}}

• Use \rtag instead of \tag.

This doesn't affect the alignment of the formula but if the formula or its name are very long, there is a danger of overlapping.

Here the code

\documentclass{article}
\usepackage{lipsum}
\usepackage{amsmath}
\newcommand*{\rtag}[1]{\tag*{\makebox[0pt][r]{(#1)}}}
\begin{document}
\lipsum[4]
\begin{align*}
\rtag{This a name larger than normal}
y = 3x
\end{align*}
\begin{center}
\begin{align*}
\rtag{Centered}
y = 3x
\end{align*}
\end{center}
\end{document}

• Do you need to encase the second align* environment in a center environment? – Mico Jul 11 '14 at 5:53
• @Mico i don't think so, the center environment can be omitted. – skpblack Jul 23 '14 at 14:18
• In other words, the center environment should be omitted, right? :-) – Mico Jul 23 '14 at 16:12