Parentheses disappear in Equation mode in ACM class

Question

The problem is that when using the font package lmodern with the ACM class acmart.cls, the parentheses tend to disappear in the final output. Without lmodern, acmart.cls gives an error. Here is the MWE:

\documentclass[sigconf, anonymous=true]{acmart}
\usepackage{lmodern}

\begin{document}

\title[XYZ]{XYZ}

\maketitle
\begin{equation}
Output = AES_{K}(0),AES_{K}(1),AES_{K}(2),...
\end{equation}
%
\bibliographystyle{ACM-Reference-Format}
\bibliography{PRNGbib}
\end{document}

I am using a lot of other math packages too. Both parentheses and curly brackets tend to disappear in the final output as shown below:

I have already tried adjusting the package order as suggested here.

Answer 1

You get warnings in your log file:

Missing character: There is no <B9> in font lmsy9!
Missing character: There is no <B9> in font lmsy9!
Missing character: There is no <BA> in font lmsy9!
Missing character: There is no <B9> in font lmsy9!
Missing character: There is no <BA> in font lmsy9!
Missing character: There is no <B9> in font lmsy9!
Missing character: There is no <BA> in font lmsy9!

(the actual output may differ in how it displays <B9> and <BA>).

The problem is that the acmart document class loads newtxmath with the option libertine, which assigns different mathcodes to ( and ), precisely "42B9 for ) and 52BA for ) and this explains the “missing character” warnings.

The standard mathcodes are, respectively, "4028 and "5029. You might get away with such problems by redefining the mathcodes:

\DeclareMathDelimiter{(}{\mathopen} {operators}{"28}{largesymbols}{"00}
\DeclareMathDelimiter{)}{\mathclose}{operators}{"29}{largesymbols}{"01}

Here's the complete code:

\documentclass[sigconf, anonymous=true]{acmart}
\usepackage{lmodern}

\DeclareMathDelimiter{(}{\mathopen} {operators}{"28}{largesymbols}{"00}
\DeclareMathDelimiter{)}{\mathclose}{operators}{"29}{largesymbols}{"01}

\begin{document}

\title[XYZ]{XYZ}

\maketitle
\begin{equation}
Output = AES_{K}(0),AES_{K}(1),AES_{K}(2),...
\end{equation}

\bibliographystyle{ACM-Reference-Format}
\bibliography{PRNGbib}

\end{document}

Note, however, that it's possible to have other mismatches between the defined mathcodes and those expected by lmodern. Also some parts of the document may use Libertine nonetheless.

Final advice: the acmart class has been carefully written to comply with the standards of ACM and affiliate conferences. Changing the appearance of the output by loading different fonts than what's defined in the class should not be done and it could be a good reason for rejection of a submission.

Answer 2

The OP's problem is different, but anyone trying to use lmodern and newtxmath together is likely to encounter the same symptoms, independent of the acmart class. In my case I was using newtxmath just for a few symbols, and the solution that worked best was to stop loading that package and instead copy out the definitions of symbols I needed from newtxmath.sty. For example (obviously this will vary depending on which symbols you need):

% from <https://tex.stackexchange.com/q/452081/78411>
\makeatletter
\newif\iftx@libertine
\newif\iftx@minion
\newif\iftx@coch
\newif\iftx@ch
\newif\iftx@stxtwo
\makeatother

\DeclareSymbolFont{lettersA}{U}{ntxmia}{m}{it}
\SetSymbolFont{lettersA}{bold}{U}{ntxmia}{b}{it}
\DeclareFontSubstitution{U}{ntxmia}{m}{it}

\DeclareMathSymbol{\uprho}{\mathord}{lettersA}{26}
\DeclareMathSymbol{\upvarphi}{\mathord}{lettersA}{39}

\DeclareSymbolFont{AMSm}{U}{ntxsym}{m}{n}
\SetSymbolFont{AMSm}{bold}{U}{ntxsym}{b}{n}
\DeclareFontSubstitution{U}{ntxsym}{m}{n}

\DeclareMathSymbol{\Game}{\mathord}{AMSm}{97}
\DeclareMathSymbol{\ggg}{\mathrel}{AMSm}{239}
\DeclareMathSymbol{\circledast}{\mathbin}{AMSm}{254}