Which version of LaTeX permits more than 16 alphabets?

Question

Sometimes I receive a message:

! LaTeX Error: Too many math alphabets used in version normal.

I know that there is a limit of 16 alphabets at most allowed to one article. However this message specified version normal, so are there any other version of LaTeX permitting more than 16 alphabets?

Answer 1

You can use more that 16 math groups (math alphabets, in particular) with XeLaTeX or LuaLaTeX; here's an example. One must also change the allocation mechanism, of course.

\documentclass{article}
\makeatletter
\def\new@mathgroup{\alloc@8\mathgroup\mathchardef\@cclvi}
\def\document@select@group#1#2#3#4{%
 \ifx\math@bgroup\bgroup\else\relax\expandafter\@firstofone\fi
 {%
 \ifmmode
   \ifnum\csname c@mv@\math@version\endcsname<\@cclvi
     \begingroup
       \escapechar\m@ne
       \getanddefine@fonts{\csname c@mv@\math@version\endcsname}#3%
       \globaldefs\@ne  \math@fonts
     \endgroup
     \expandafter\extract@alph@from@version
         \csname mv@\math@version\expandafter\endcsname
         \expandafter{\number\csname
                       c@mv@\math@version\endcsname}%
          #1%
     \global\advance\csname c@mv@\math@version\endcsname\@ne
   \else
     \let#1\relax
     \@latex@error{Too many math alphabets used
                   in version \math@version}%
        \@eha
  \fi
 \else \expandafter\non@alpherr\fi
 #1{#4}%
 }%
}
\def\select@group#1#2#3#4{%
 \ifx\math@bgroup\bgroup\else\relax\expandafter\@firstofone\fi
 {%
 \ifmmode
  \ifnum\csname c@mv@\math@version\endcsname<\@cclvi
     \begingroup
       \escapechar\m@ne
       \getanddefine@fonts{\csname c@mv@\math@version\endcsname}#3%
       \globaldefs\@ne  \math@fonts
     \endgroup
     \init@restore@version
     \xdef#1{\noexpand\use@mathgroup\noexpand#2%
             {\number\csname c@mv@\math@version\endcsname}}%
     \global\advance\csname c@mv@\math@version\endcsname\@ne
   \else
     \let#1\relax
     \@latex@error{Too many math alphabets used in
                   version \math@version}%
        \@eha
   \fi
 \else \expandafter\non@alpherr\fi
 #1{#4}%
 }%
}
\makeatother
\DeclareMathAlphabet{\mA}{OT1}{pcr}{m}{n}
\DeclareMathAlphabet{\mB}{OT1}{pcr}{m}{it}
\DeclareMathAlphabet{\mC}{OT1}{pcr}{b}{n}
\DeclareMathAlphabet{\mD}{OT1}{pcr}{b}{it}
\DeclareMathAlphabet{\mE}{OT1}{ptm}{m}{n}
\DeclareMathAlphabet{\mF}{OT1}{ptm}{m}{it}
\DeclareMathAlphabet{\mG}{OT1}{ptm}{b}{n}
\DeclareMathAlphabet{\mH}{OT1}{ptm}{b}{it}
\DeclareMathAlphabet{\mI}{OT1}{pag}{m}{n}
\DeclareMathAlphabet{\mJ}{OT1}{pag}{m}{it}
\DeclareMathAlphabet{\mK}{OT1}{pag}{b}{n}
\DeclareMathAlphabet{\mL}{OT1}{pag}{b}{it}
\DeclareMathAlphabet{\mM}{OT1}{pbk}{m}{n}
\DeclareMathAlphabet{\mN}{OT1}{pbk}{m}{it}
\DeclareMathAlphabet{\mO}{OT1}{pbk}{b}{n}
\DeclareMathAlphabet{\mP}{OT1}{pbk}{b}{it}

\begin{document}
$
\mathbf{X}
\mathit{X}
\mathsf{X}
\mathtt{X}
\mA{X}
\mB{X}
\mC{X}
\mD{X}
\mE{X}
\mF{X}
\mG{X}
\mH{X}
\mI{X}
\mJ{X}
\mK{X}
\mL{X}
\mM{X}
\mN{X}
\mO{X}
\mP{X}
$
\end{document}

One could do without copying all that stuff with a simpler patch; the following code should replace all that in the previous one is between \makeatletter and \makeatother:

\usepackage{etoolbox}
\makeatletter
\def\new@mathgroup{\alloc@8\mathgroup\mathchardef\@cclvi}
\patchcmd{\document@select@group}{\sixt@@n}{\@cclvi}{}{}
\patchcmd{\select@group}{\sixt@@n}{\@cclvi}{}{}
\makeatother

Compiling the document with xelatex or lualatex will show the following horror; of course you'll have better use cases.

Important remark

As Khaled Hosny quite rightly observes, there is a very important limitation: this can work only for math alphabets; it's impossible to define \mathchar values that use the extended set (the XeTeX or LuaTeX extensions should be used). Thus one has to be careful when using math symbol fonts which must be loaded in memory before the math alphabets. So, if , say, stmaryrd is loaded, it's best to ensure that a formula using it is typeset before using the new math alphabets; a \sbox0{$\Ydown$} in the preamble should be sufficient, because so a math group will be permanently allocated for stmaryrd.