multiple algorithm2e algorithms in two column documents

Question

I tried this example Place four algorithms (algorithm2e) in a subfigure and arrange them in two rows and two columns on two column documents. It doesn't work. The error message is

! LaTeX Error: [H] in two columns mode is not allowed for algorithms.

Is there anyway to go?

The code example is:

\documentclass[twocolumn]{article}
\usepackage{algorithm2e}
\usepackage{caption}
\usepackage{subcaption}


\newcommand{\myalgorithm}{%
\begin{algorithm*}[H]
\SetAlgoLined
\KwData{this text}
\KwResult{how to write algorithm with \LaTeX2e }
initialization\;
\While{not at end of this document}{
read current\;
\eIf{understand}{
go to next section\;
current section becomes this one\;
}{
go back to the beginning of current section\;
}
}
\end{algorithm*}}
\begin{document}

\begin{figure}
    \begin{subfigure}{.5\textwidth}
        \myalgorithm
        \caption{How to write algorithms}
    \end{subfigure}% need this comment symbol to avoid overfull hbox
    \begin{subfigure}{.5\textwidth}
        \myalgorithm
        \caption{How to write algorithms}
    \end{subfigure}\\
    \begin{subfigure}{.5\textwidth}
        \myalgorithm
        \caption{How to write algorithms}
    \end{subfigure}%
    \begin{subfigure}{.5\textwidth}
        \myalgorithm
        \caption{How to write algorithms}
    \end{subfigure}
\caption{Main caption}
\end{figure}


\end{document}

Answer 1

algorithm2e provides its own [H] float parameter, which sidesteps setting its contents as a float. However, in twocolumn mode, it produces an error. I'm not sure why. You can avoid this by setting \@latex@error to \@gobble temporarily. Using your example, I've added a \removelatexerror macro inside a \begingroup...\endgroup. More specifically, the definition

\makeatletter
\newcommand{\removelatexerror}{\let\@latex@error\@gobble}
\makeatother

is placed inside a group, inside \myalgorithm:

\newcommand{\myalgorithm}{%
\begingroup
\removelatexerror% Nullify \@latex@error
\begin{algorithm*}[H]
%...
\end{algorithm*}
\endgroup}

Also, since you're spreading the 4 algorithms across both columns, it's best to use figure* rather than figure:

Obviously you won't be using \myalgorithm in your actual document. You could just place \removelatexerror inside each of the subfigure environments.

Answer 2

I had similar issues...

I simply removed [H] from the code as below.

\begin{algorithm*}[H]

to

\begin{algorithm*}

Then the issue solved.