acmsmall breaks line number alignments of algorithms

Question

I am formatting an article with one of the ACM journal formats: acmsmall. However, when I look at algorithms, I noticed that the lines of my algorithm lost their indentation.

This problem does not occur in article class.

I have prepared a minimal example to demostrate the issue.

\documentclass{acmsmall}
%\documentclass{article}

\usepackage{algorithm}
\usepackage[noend]{algpseudocode} 

\begin{document}
    \begin{algorithm}
        \caption{MyAlgorithm}
        \begin{algorithmic}[1]
            \State $A \gets X$
            \State $A \gets Y$
            \State $A \gets Z$
            \State $A \gets X$
            \State $A \gets Y$
            \State $A \gets Z$
            \State $A \gets X$
            \State $A \gets Y$
            \State $A \gets Z$
            \State $A \gets X$
            \State $A \gets Y$
            \State $A \gets Z$
        \end{algorithmic}
    \end{algorithm}
\end{document}

I have attached the screenshots of both acmsmall and article. As you can see, after line 10, the indentation of acmsmall is broken.

How can I fix the problem?

Answer 1

The acmsmall class is causing the numbers to be centered rather than right-aligned. You can correct this by redefining \alglinenumber as follows (updated to get fontsize):

\newcommand{\myalgnumfont}{\fontsize{8pt}{9pt}\selectfont}
\algrenewcommand{\alglinenumber}[1]{\myalgnumfont #1:}

in the preamble.

\documentclass{acmsmall}
%\documentclass{article}

\usepackage{algorithm}
\usepackage[noend]{algpseudocode} 

\newcommand{\myalgnumfont}{\fontsize{8pt}{9pt}\selectfont}
\algrenewcommand{\alglinenumber}[1]{\hss\myalgnumfont #1:}

\begin{document}
    \begin{algorithm}
        \caption{MyAlgorithm}
        \begin{algorithmic}[1]
            \State $A \gets X$
            \State $A \gets Y$
            \State $A \gets Z$
            \State $A \gets X$
            \State $A \gets Y$
            \State $A \gets Z$
            \State $A \gets X$
            \State $A \gets Y$
            \State $A \gets Z$
            \State $A \gets X$
            \State $A \gets Y$
            \State $A \gets Z$
        \end{algorithmic}
    \end{algorithm}
\end{document}

The standard algorithmic definition use \footnotesize to set the fontsize. The problem is that acmsmall redefines the \footnotesize to

\newcommand{\footnotesize}{%
    \@setfontsize\footnotesize\@viiipt{9\p@}%
    \abovedisplayskip 4\p@ \@plus \p@
    \belowdisplayskip \abovedisplayskip
    \abovedisplayshortskip 4\p@ \@minus \p@
    \belowdisplayshortskip 4\p@ \@minus \p@
    \def\@listi{%
        \leftmargin\leftmargini
        \topsep 4\p@ \@plus \p@
        \parsep \z@ \@plus .5\p@
        \itemsep \p@ \@plus .7\p@}
}%

The problem here is the final \itemsep which in size10.clo loaded by article.cls is

   \def\@listi{\leftmargin\leftmargini
               \topsep 3\p@ \@plus\p@ \@minus\p@
               \parsep 2\p@ \@plus\p@ \@minus\p@
               \itemsep \parsep}%

In particular acmsmall is adding some glue to the end of \itemsep, which then affects the label alignment.