How to fix this amsmath warning about redefining \vec

Question

I am using the pss(b) template, which starts with,

\documentclass[pss]{wiley2sp} % provides pss two-column style
\usepackage{amsmath}
%\usepackage{bm}              % uncomment these two packages if you
%\usepackage{w-greek}         % need extended greek-letter functionality in math mode

I always got this warning:

Package amsmath Warning: Unable to redefine math accent \vec.

Does anyone know how to fix this problem?

Answer 1

load amsmath first:

\RequirePackage{amsmath}
\documentclass[pss]{wiley2sp} % provides pss two-column style
...

Then amsmath defines the \vec at first and wiley2sp will redefine it.

Answer 2

This "problem" is inherent to the class you're using.

Here's what's happening: You load wiley2sp, which sets up the document structure. It also (re)defines the macro \vec:

\if@mathematic
   \def\vec#1{\ensuremath{\mathchoice
                     {\mbox{\boldmath$\displaystyle\mathbf{#1}$}}
                     {\mbox{\boldmath$\textstyle\mathbf{#1}$}}
                     {\mbox{\boldmath$\scriptstyle\mathbf{#1}$}}
                     {\mbox{\boldmath$\scriptscriptstyle\mathbf{#1}$}}}}
\else
   \def\vec#1{\ensuremath{\mathchoice
                     {\mbox{\boldmath$\displaystyle#1$}}
                     {\mbox{\boldmath$\textstyle#1$}}
                     {\mbox{\boldmath$\scriptstyle#1$}}
                     {\mbox{\boldmath$\scriptscriptstyle#1$}}}}
\fi

This will print \vec{<stuff>} in bold math font. Yes, it actually redefines the macro from a former \mathaccent to the above.

Now you load amsmath, which cycles through a number of math accents and reconfigures them. Here's an extract from the actual code:

\def\@tempa#1{\@xp\@tempb\meaning#1\@nil#1}
\def\@tempb#1>#2#3 #4\@nil#5{%
  \@xp\ifx\csname#3\endcsname\mathaccent
    \@tempc#4?"7777\@nil#5%
  \else
    \PackageWarningNoLine{amsmath}{%
      Unable to redefine math accent \string#5}%
  \fi
}
\def\@tempc#1"#2#3#4#5#6\@nil#7{%
  \chardef\@tempd="#3\relax\set@mathaccent\@tempd{#7}{#2}{#4#5}}
\@tempa{\hat}
\@tempa{\check}
\@tempa{\tilde}
\@tempa{\acute}
\@tempa{\grave}
\@tempa{\dot}
\@tempa{\ddot}
\@tempa{\breve}
\@tempa{\bar}
\@tempa{\vec}

The above code is prefaced by the following documentation:

We redefine the standard math accent commands call \mathaccentV, using the mathgroup/encoding-number information embedded in their previous definitions. If the definition of an accent command does not have the expected form, we leave the accent command alone, but give a warning.

You'll notice the set of redefinitions require the former definition of the math accent to start with \mathaccent (as part of the \ifx condition in \@tempb). Since wiley2sp redefined \vec to mean something completely different (not a \mathaccent anymore), amsmath reports the warning.

A way around this would be to capture the definition of \vec before wiley2sp redefines it, and restore it before amsmath checks to redefine it. The following achieves this:

\let\oldvec\vec% Store \vec in \oldvec
\documentclass{wiley2sp}
\let\vec\oldvec% Restore \vec from \oldvec

Note that, if this is a publisher-related style or class, they most likely want their \vectors printed in a specific format. So, removing this formatting of \vectors is probably not advised.