Can't modify algorithm2e caption numbering

Question

I want to change the numbering of one algorithm from Algorithm 5 to Algorithm 2.1.

I've tried all these methods:

Change caption number of an algorithm

https://github.com/hadizadeh/Latex_algorithm

No matter how I modify the code, the result is always the same. Here is an example.

\usepackage[ruled, vlined, linesnumbered, nofillcomment]{algorithm2e}
\usepackage{algpseudocode}

...

\begin{algorithm}[H]
    \renewcommand{\thealgorithm}{2.1}
    \caption{Name of the algorithm}
    test1\\
    test2
\end{algorithm}

It doesn't matter if I put \renewcommand{\thealgorithm}{2.1} inside or outside the algorithm environment.

Thanks in advance.

Answer 1

This code will make algorithm number be section number . algorithm number

\documentclass[12pt,a4paper]{article}

\usepackage[ruled, vlined, linesnumbered, nofillcomment]{algorithm2e}
\usepackage{algpseudocode}

%****************************************** added <<<<<<<<<<<<<<
\makeatletter
\renewcommand{\fnum@algocf}{\AlCapSty{\AlCapFnt\algorithmcfname\nobreakspace\thesection.\thealgocf}}%
\makeatother
%******************************************

\begin{document}
    
    \setcounter{section}{3}% test section numbers   
    \setcounter{algocf}{5}% test algo numbers
        
    \section{A section} 
    
    \begin{algorithm}
        \caption{Name of the algorithm}
        test1\\
        test2
    \end{algorithm}

\end{document}

The caption separator can be controlled using \SetAlgoCaptionSeparator{sep} (default :)

If you want to reset the algorithm counter at the beginning of a section add to the preamble

\let\oldsection\section
\renewcommand{\section}{\setcounter{algocf}{0}\oldsection}

OPTION

This is another option using the dcounter package, using the section number and also will reset the algorithm counter starting a new section of so desired.

\documentclass[12pt,a4paper]{article}

\usepackage[ruled, vlined, linesnumbered, nofillcomment]{algorithm2e}
\usepackage{algpseudocode}

 \SetAlgoCaptionSeparator{} % default :

\usepackage{dcounter} % added <<<<<<<<<<<<<<<<<
\countstyle{section}%
\DeclareDynamicCounter{algocf}%  reset the algorithm counter starting a new section
 
\begin{document}
    
    \setcounter{section}{3}% test section numbers   
                
    \section{A section} 
    
    \begin{algorithm}
        \caption{Name of the algorithm 1}
        test1\\
        test2
    \end{algorithm}

    \begin{algorithm}
        \caption{Name of the algorithm 2}
        test1\\
        test2
    \end{algorithm}
    
    \section{Another section}   
    
    \begin{algorithm}
        \caption{Name of the algorithm 3}
        test1\\
        test2
    \end{algorithm}

\end{document}