Bold mathematics in eulervm

Question

The eulervm package documentation indicates that one should use \mathbold instead of \mathbf to produce bold maths.

Could one write \renewcommand{\mathbf}{\mathbold}? What are the side effects?

Answer 1

The standard definition for \mathbf is

\DeclareMathAlphabet{\mathbf}{OT1}{cmr}{bx}{n}

This has the effect that math symbols declared as \mathalpha (essentially Latin letters, uppercase Greek letters, digits and accents) that happen to be in the argument of \mathbf are typeset from the stated font.

The eulervm package uses a different font for bold:

\DeclareMathAlphabet{\mathbold}{U}{zeur}{b}{n}

and also redeclares many symbols (for instance, also lowercase Greek letter are allowed in the argument of \mathbold).

Since the effect of \mathbold is different from \mathbf it's a good decision to use a different name. However

\renewcommand{\mathbf}{\mathbold}

is perfectly safe. What happens is that when TeX sees \mathbf it replaces it by \mathbold and then proceeds to look for the arguments to \mathbold. (Actually, as Werner showed, there's no argument to \mathbold, but this is immaterial.)

With this redefinition you lose the original meaning of \mathbf, but using eulervm it doesn't seem to be important. Would you keep it for some reason, it's better to say

\usepackage{letltxmacro}
\LetLtxMacro{\originalmathbf}{\mathbf}

before redefining \mathbf.

Answer 2

Yes you can write \renewcommand{\mathbf}{\mathbold}. Why? Let's look at the definitions of both (using a definition of \pshow from The definitions of LaTeX commands on the UK TeX FAQ):

\documentclass{article}
\def\pshow#1{{\let\protect\show #1}}% http://www.tex.ac.uk/cgi-bin/texfaq2html?label=ltxcmds
\pshow\mathbf
\usepackage{eulervm}% http://ctan.org/pkg/eulervm
\pshow\mathbold
\makeatletter
\show\select@group
\makeatother
\begin{document}
Dummy text.
\end{document}

yields in the .log:

> \mathbf =macro:
->\select@group \mathbf  \M@OT1 \OT1/cmr/bx/n .
\mathbf ->\protect \mathbf  

l.3 \pshow\mathbf


(c:/texlive/2011/texmf-dist/tex/latex/eulervm/eulervm.sty
Package: eulervm 2005/01/11 v4.0 (WaS)
)
> \mathbold =macro:
->\select@group \mathbold  \M@U \U/zeur/b/n .
\mathbold ->\protect \mathbold  

l.5 \pshow\mathbold


> \select@group=macro:
#1#2#3#4->\ifx \math@bgroup \bgroup \else \relax \expandafter \@firstofone \fi 
{\ifmmode \ifnum \csname c@mv@\math@version \endcsname <\sixt@@n \begingroup \e
scapechar \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 }}\gl
obal \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}}.
l.7 \show\select@group

Note that neither \mathbf nor \mathbold take an argument. There is a secondary macro called from both \mathbf and \mathbold that takes the argument supplied: \select@group. The first three arguments taken by \select@group is supplied within \mathbf and \mathbold, while the fourth is supplied additionally after each macro.

What are the side effects? You can't use the original definition of \mathbf. Some people circumvent this by using

\let\oldmathbf\mathbf% Store contents of \mathbf in \oldmathbf
\let\mathbf\mathbold% Rename \mathbf to \mathbold