# How to mark equation number but not change the reference text?

I would like to mark a few equations as special by adding an asterisk (or some other symbol) to the equation number. I accomplish this as follows:

\documentclass{article}

\usepackage{amsmath}

\newcommand{\markThisEquationSpecial}{\refstepcounter{equation}\tag{{\theequation}*}}

\begin{document}
Here is an important equation:
$$\label{eq:important} S_{\text{EH}} = \int \frac{m_{p}^{2}}{2}R \sqrt{-g} d^{4}x\,. \markThisEquationSpecial$$
Here is an unimportant equation:
$$\label{eq:unimportant} S_{\text{M}} = \int \frac{-1}{4}F_{ab}F^{ab} \sqrt{-g} d^{4}x\,.$$

The unimportant equation is referenced as Eq.~\eqref{eq:unimportant}.
The important equation is referenced as Eq.~\eqref{eq:important}.
Notice that the asterisk has come along for the ride in the reference.
I would like it to appear as Eq.~(1).
\end{document}


This appears as follows:

How can I prevent the asterisk for making it into the text for the \ref?

Alternatively, is there some way to put a (*) to the left of the equation, mirroring the location of the equation number (1), as a way of marking an equation as important?

• Important equation authors usually put in frame ... – Zarko Jun 2 '15 at 21:08
• @Zarko I have seen \boxed{} equations, but I'm afraid it looks a bit out of place among other equations. It's a matter of taste. – duetosymmetry Jun 2 '15 at 21:11
• Is there a chance your readers might become confused if the cross-reference to some equation looks like (1) but there's no equation labelled as such anywhere in the document (as the equation is labelled (1*))? Will you provide an explanatory blurb in the text (maybe in a footnote) to alert readers to this "feature"? – Mico Jun 2 '15 at 21:15

## 3 Answers

Here is a relatively simple alternate solution using flalign:

\documentclass{article}
\usepackage{amsmath}
\usepackage{mathabx}% extra symbols

\begin{document}
Here is an important equation:
\begin{flalign}\label{eq:important}
\Asterisk && S_{\text{EH}} = \int \frac{m_{p}^{2}}{2}R \sqrt{-g} d^{4}x\,.&&
\end{flalign}

Here is an unimportant equation:
$$\label{eq:unimportant} S_{\text{M}} = \int \frac{-1}{4}F_{ab}F^{ab} \sqrt{-g} d^{4}x\,.$$

The unimportant equation is referenced as Eq.~\eqref{eq:unimportant}.
The important equation is referenced as Eq.~\eqref{eq:important}.
\end{document}


Come to think of it, it works on the right side too.

\begin{flalign}\label{eq:important}
&& S_{\text{EH}} = \int \frac{m_{p}^{2}}{2}R \sqrt{-g} d^{4}x\,.&&\Asterisk
\end{flalign}


As said @Mico in his comment, adding * to equation number and than not used in referencing lead to confusion. Since you not liked to emphasize the importance of equation with frame or shadow box etc (what provide for example empheq package), than please see if the importance of equation is adequate market as you can see here:

Code :

\documentclass{article}

\usepackage{amsmath}
\usepackage{graphicx,pifont}

\newcommand{\alert}[1][3em]{%
\marginpar[\raisebox{-#1}{\quad\huge\ding{43}\quad}]%
{\raisebox{-#1}{\quad\reflectbox{\huge\ding{43}}}}
}

\begin{document}
Here is an important equation:
\alert$$\label{eq:important} S_{\text{EH}} = \int \frac{m_{p}^{2}}{2}R \sqrt{-g} d^{4}x\,.$$
Here is an unimportant equation:
$$\label{eq:unimportant} S_{\text{M}} = \int \frac{-1}{4}F_{ab}F^{ab} \sqrt{-g} d^{4}x\,.$$

The unimportant equation is referenced as Eq.~\eqref{eq:unimportant}.
The important equation is referenced as Eq.~\eqref{eq:important} \dots and marked on page border with \ding{43}.
\end{document}


Instead of \ding{43} you can select any symbol according to your taste.

Use the original "LaTeX \label" rather than the updated amsmath \label:

\documentclass{article}

\usepackage{amsmath}

\newcommand{\markThisEquationSpecial}{%
\refstepcounter{equation}%
\tag{{\theequation}*}%
}
\makeatletter
\newcommand{\ltxlabel}{\ltx@label}% Original LaTeX \label
\makeatother

\begin{document}
Here is an important equation:
$$\label{eq:important}\ltxlabel{eq:important2} S_{\text{EH}} = \int \frac{m_{p}^{2}}{2}R \sqrt{-g} d^{4}x\,. \markThisEquationSpecial$$
Here is an unimportant equation:
$$\label{eq:unimportant} S_{\text{M}} = \int \frac{-1}{4}F_{ab}F^{ab} \sqrt{-g} d^{4}x\,.$$

The unimportant equation is referenced as Eq.~\eqref{eq:unimportant}.
The important equation is referenced as Eq.~\eqref{eq:important}.
Notice that the asterisk has come along for the ride in the reference.
I would like it to appear as Eq.~\eqref{eq:important2}.
\end{document}