# Labeling an equation with letters [duplicate]

Is there a way to label an equation with letters instead of numbers? For instance,

$$\label{Problem} \phi'(t)=f(t, \phi(t)).$$

• Yes. Could you elaborate on the use-case? Do you want all equations labelled with letters or just some? What should the letter format be... (A), (B), ... or (a), (b), ... or something different altogether? – Werner Mar 2 '15 at 23:09
• And welcome to TeX.SX! – egreg Mar 2 '15 at 23:29
• Please post complete code i.e. a small, compilable document. That is much more useful than a fragment. – cfr Mar 3 '15 at 0:59
• @Nicolas How is this a duplicate? That question explicitly says neither a number nor a letter, which is not the case here. (The solution might be similar but that's a different issue.) – cfr Mar 3 '15 at 1:01
• Do you want all equations labelled with letters or just some? Just some. – José David Campos F Mar 3 '15 at 3:03

With the alphalph package, after 26 equations, they become AA, AB, AC, etc. If one uses \alphalph, the letters are in lowercase.

\documentclass{article}
\usepackage{alphalph}
\def\theequation{\AlphAlph{\value{equation}}}
\begin{document}
$$y=x$$
$$y=x^2$$
$$y=x^3$$
\end{document}


You can simply redefine the counter to display with letters with:

\renewcommand{\theequation}{\alph{equation}}


If you want Uppercase letters use:

\renewcommand{\theequation}{\Alph{equation}}


You can even use combined Letters and numbers. Incorporating the section number as a number, and the equation as a letter:

\renewcommand{\theequation}{\arabic{section}.\Alph{equation}}


Full example...

\documentclass{article}
\usepackage{amssymb}

\renewcommand{\theequation}{\alph{equation}}

\begin{document}

\section{Lower Case Letter}
$$y=x$$
$$y=x^2$$
$$y=x^3$$

\section{Upper Case Letter}
\renewcommand{\theequation}{\Alph{equation}}
$$y=x$$
$$y=x^2$$
$$y=x^3$$

\section{Section number and Upper Case Letter}
\renewcommand{\theequation}{\arabic{section}.\Alph{equation}}
$$y=x$$
$$y=x^2$$
$$y=x^3$$

\end{document}


• Of course this fails of you have more than 26 equations. You can do set the counter to 0 explicitly at the beginning of each section with \setcounter{equation}{0}. Then with the section number and letter option I mentioned above you can have 26 equations per section. The same follows logically for all levels of sectioning -- chapter, subsection etc. – tmgriffiths Mar 3 '15 at 6:46