How to replace mathptmx \sum with CM \sum?

Question

I would like to replace the rather ugly mathptmx \sum operator with the equivalent Computer Modern one.

Answer 1

Here's a compilation of display-style \sum symbols provided by various font packages.

I'd say that the summation symbol provided by the mtpro2 package is closest to the one provided by the Computer Modern family, while still providing the genuine "Times Roman" look. Incidentally, the full mtpro2 package isn't free of charge. However, its lite subset, which is all that's needed to produce the good-looking \sum symbol, may indeed be downloaded free of charge.

Here's the code that generated the preceding four lines (run consecutively for each choice of font family).

\documentclass{article}
\usepackage{array}
%\usepackage{mathptmx}
%\usepackage{newtxmath}
\renewcommand{\rmdefault}{ptm} \usepackage[lite]{mtpro2}
\begin{document}
\begin{tabular}{@{}>{\ttfamily}p{4cm}>{$\displaystyle}l<{$}}    
Times Roman, mtpro2 & \sum
\end{tabular}
\end{document}