Equations – Marking Equation Numbers Without Changing Reference Text

counterscross-referencingequationslabels

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

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:
MWE

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?

Best Answer

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

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

impartant equations

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}

more important

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