I would like to use a big mathcal R for the Ramanujan summation. From a previous question (Math operator resizing in autosized brackets), I got
\documentclass{article}
\def\xRsum#1#2{\hbox{#1$#2\mathcal R$}}
\newcommand\Rsum{\mathop{%
\mathchoice
{\xRsum\huge\displaystyle}%
{\xRsum{}\displaystyle}%
{\xRsum{}\scriptstyle}%
{\xRsum{}\scriptscriptstyle}%
}}
\begin{document}
$$\sum_{k=1}^{+\infty}k\neq-\frac1{12}\qquad\Rsum_{k=1}^{+\infty}k=-\frac1{12}$$
$$\frac1{\Rsum_{k=1}^{+\infty}\frac1{k^2}}=\frac1{\sum_{k=1}^{+\infty}\frac1{k^2}}$$
\end{document}
but it does not correct produce output.
You can see everything is aligned very badly.

\displaystylevariation should actually upscale a lighter-weight math font, such asKPMath-Light, while your\textstylrvariation should use something like KPMath-Regular. If you have to use a math font that doesn’t come in light weight (and most don’t), you can at least use\mathbfscrversus\mathscr` for consistency. – Davislor Nov 24 '22 at 14:01\mathopfor series-like spacing and limits. – Davislor Nov 24 '22 at 14:02