Math & Science ⇒ Changing an equation number to a symbol

[Cham]

For a very rare case, I need to completely change the number of a particular equation to a symbol (\mathcal{A}). How can I do this, without affecting all the other equation numbers ?

Here's a MWE to work with :

Code: Select all

\documentclass[12pt,letterpaper]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{mathtools}

\begin{document}

Some equation :
	\begin{equation}
		y(x) = a x^2 + b x + c.
	\end{equation}
The following equation should have $\mathcal{A}$ as a "number" :
	\begin{equation}
		\label{test}
		x = \frac{- b \pm \sqrt{b^2 - 4 a c}}{2 a}.
	\end{equation}
A few comments about equation \eqref{test} :
	\begin{equation}
		y(z) = a + b z.
	\end{equation}
\end{document}

The reference should also show the correct symbol inside the text.

[cgnieder]

Use \tag:

Code: Select all

\documentclass[12pt,letterpaper]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{mathtools}
 
\begin{document}
 
Some equation:
\begin{equation}
  y(x) = a x^2 + b x + c.
\end{equation}
The following equation should have $\mathcal{A}$ as a  ``number'':
\begin{equation}
  \label{test}
  x = \frac{- b \pm \sqrt{b^2 - 4 a c}}{2 a}. \tag{$\mathcal{A}$}
\end{equation}
A few comments about equation \eqref{test}:
\begin{equation}
  y(z) = a + b z.
\end{equation}

\end{document}

Regards

[Cham]

Wow ! Perfect and so simple ! I didn't knew that one. Thanks !