# How to put a custom tag to the algorithm environment?

I am trying a way to number algorithms 1a, 1b, 1c, 2a, 2b, 2c, etc. As I understand from the documentation of the algorithms package here, I can number them after the part, chapter, section and so on. In this related topic they discuss how to customize the number. But I don't want the number, I would like to also have letters: for example, in the following MWE, I would like to have the two algorithms numbered (and therefore referenced to as) 1a and 1b.

\documentclass{article}
\usepackage{algorithm}
\usepackage{algpseudocode}
\begin{document}
Algorithm~\ref{MyAlg} does things in a way. Algorithm~\ref{MyOtherAlg} does things in some other way.
\begin{algorithm}\caption{My algorithm}\label{MyAlg}
\begin{algorithmic}[1]
\State Do stuff.
\end{algorithmic}
\end{algorithm}
\begin{algorithm}\caption{My other algorithm}\label{MyOtherAlg}
\begin{algorithmic}[1]
\State Do stuff differently.
\end{algorithmic}
\end{algorithm}
\end{document}


Any idea on how to achieve this?

• And what represents the "1"? Is it associated to a section? Jun 18, 2015 at 17:12
• no, it can be a custom number Jun 18, 2015 at 17:24
• What is a sequential counter? A user-defined one? Jun 18, 2015 at 17:25
• See my edit: a custom number. It might as well not be there. For example I may want to number them simply "A" and "B", let's say. Hand curated numbering. Jun 18, 2015 at 17:28
• Please see my recently updated answer. Something like that (see the las to examples after "Update")? Jun 18, 2015 at 17:30

All you have to do is to redefine the command \thealgorithm which controls the representation for the algorithm counter. For example, to number them using alphabetic lower-case characters and to prepend the section number you would do

\renewcommand\thealgorithm{\thesection\alph{algorithm}}


Assuming that you want the counter to reset at every section, you will also need

\usepackage{chngcntr}
\counterwithin{algorithm}{section}


A complete example.

\documentclass{article}
\usepackage{algorithm}
\usepackage{algpseudocode}
\usepackage{chngcntr}

\counterwithin{algorithm}{section}
\renewcommand\thealgorithm{\thesection\alph{algorithm}}

\begin{document}
\section{Test section}

Algorithm~\ref{MyAlg} does things in a way. Algorithm~\ref{MyOtherAlg} does things in some other way.
\begin{algorithm}\caption{My algorithm}\label{MyAlg}
\begin{algorithmic}[1]
\State Do stuff.
\end{algorithmic}
\end{algorithm}
\begin{algorithm}\caption{My other algorithm}\label{MyOtherAlg}
\begin{algorithmic}[1]
\State Do stuff differently.
\end{algorithmic}
\end{algorithm}

\end{document}


The result:

## Update:

Same idea if a user-defined counter is to be used:

\documentclass{article}
\usepackage{algorithm}
\usepackage{algpseudocode}
\usepackage{chngcntr}

\newcounter{mycount}
\counterwithin{algorithm}{mycount}
\refstepcounter{mycount}
\renewcommand\thealgorithm{\arabic{mycount}\alph{algorithm}}

\begin{document}
\section{Test section}

Algorithm~\ref{MyAlg} does things in a way. Algorithm~\ref{MyOtherAlg} does things in some other way.
\begin{algorithm}\caption{My algorithm}\label{MyAlg}
\begin{algorithmic}[1]
\State Do stuff.
\end{algorithmic}
\end{algorithm}
\begin{algorithm}\caption{My other algorithm}\label{MyOtherAlg}
\begin{algorithmic}[1]
\State Do stuff differently.
\end{algorithmic}
\end{algorithm}

\end{document}


or to have the numbering with upper-case alphabetical characters:

\documentclass{article}
\usepackage{algorithm}
\usepackage{algpseudocode}

\renewcommand\thealgorithm{\Alph{algorithm}}

\begin{document}
\section{Test section}

Algorithm~\ref{MyAlg} does things in a way. Algorithm~\ref{MyOtherAlg} does things in some other way.
\begin{algorithm}\caption{My algorithm}\label{MyAlg}
\begin{algorithmic}[1]
\State Do stuff.
\end{algorithmic}
\end{algorithm}
\begin{algorithm}\caption{My other algorithm}\label{MyOtherAlg}
\begin{algorithmic}[1]
\State Do stuff differently.
\end{algorithmic}
\end{algorithm}

\end{document}


The result:

• Can we do something like this: For 2 algorithms Algorithm 2(a) and Algorithm 2(b) and the rest of the Algorithms like Algorithm 1, Algorithm 3, etc follow the normal naming and numbering styles? Aug 16, 2021 at 11:44