Compatibility between amsmath and exscale

Question

Both the amsmath package and the exscale package define the delimiter macros \big, \Big, \bigg and \Bigg based on the internal macro \bBigg@. However, as the following minimal example reveals the amsmath and exscale versions of \bBigg@ have a different meaning:

\documentclass{article}

\usepackage{etoolbox}

\usepackage{lmodern}

\usepackage{amsmath}

\show\big
%% > \big=\long macro:
%% ->\bBigg@ \@ne .

\csshow{bBigg@}
%% > \bBigg@=macro:
%% #1#2->{\@mathmeasure \z@ {\nulldelimiterspace \z@ }{\left #2\vcenter to#1\big@size {}\right .}\box \z@ }.

\usepackage{exscale}

\show\big
%% > \big=macro:
%% ->\bBigg@ \@ne .

\csshow{bBigg@}
%% > \bBigg@=macro:
%% #1#2->{\hbox {$\left #2\vcenter to#1\big@size {}\right .\n@space $}}.

\begin{document}

\noindent
\Huge \(\big(\sum_{i=1}^{N}i\big)\)

\end{document}

Does this mean that I might get different results, depending on whether the amsmath package is loaded before or after the exscale package? Or are the two versions of \bBigg@ interchangeable so that the package loading order essentially doesn’t matter?

Answer 1

Three examples

Without any package

\documentclass{article}
\usepackage{lmodern}
\begin{document}
$\sum_\sum$

\Huge$\sum_\sum$
\end{document}

With exscale

\documentclass{article}
\usepackage{lmodern}
\usepackage{exscale}
\begin{document}
$\sum_\sum$

\Huge$\sum_\sum$
\end{document}

With amsmath

\documentclass{article}
\usepackage{lmodern}
\usepackage{amsmath}
\begin{document}
$\sum_\sum$

\Huge$\sum_\sum$
\end{document}

With exscale and amsmath

\documentclass{article}
\usepackage{lmodern}
\usepackage{exscale,amsmath}
\begin{document}
$\sum_\sum$

\Huge$\sum_\sum$
\end{document}

With amsmath and without lmodern

\documentclass{article}
\usepackage{amsmath}
\begin{document}
$\sum_\sum$

\Huge$\sum_\sum$
\end{document}

Conclusions

The lmodern family has the extension symbol font in only one size, namely lmex10. With amsmath and the standard Computer Modern fonts, the "scaled" fonts cmex7 and cmex5 will be used, but of course this isn't possible if lmodern is loaded.

The definition of \bBigg@ given in exscale is obviously modelled on that by amsmath, but lacks its infrastructure, so it falls back to the standard LaTeX method.

If exscale is necessary because Latin Modern fonts are preferred, then exscale should be loaded before amsmath, so that the definition of \bBigg@ is eventually given by the latter.