Implement AMSMath's \uproot and \leftroot

[gujunhk]

\uproot and \leftroot can run in GitHub Markdown(maybe MathJax):

$$\sqrt[\uproot{16}\leftroot{-2}\frac1n]{1+\frac{\sqrt{2}}{n}}$$

$$\sqrt[\uproot{16}\leftroot{-2}\frac1n]{1+\frac{\sqrt{2}}{n}}$$

I wish they'll also be rendered in KaTeX 🤞

[edemaine]

Thanks for the feature request! I didn't know these were in amsmath, and I agree they'd be useful.

If I'm reading the source code correctly:

\def\r@@t#1#2{\setboxz@h{$\m@th#1\sqrtsign{#2}$}%
 \dimen@\ht\z@\advance\dimen@-\dp\z@
 \setbox\@ne\hbox{$\m@th#1\mskip\uproot@ mu$}%
 \advance\dimen@ by1.667\wd\@ne
 \mkern-\leftroot@ mu\mkern5mu\raise.6\dimen@\copy\rootbox
 \mkern-10mu\mkern\leftroot@ mu\boxz@}

it looks like \uproot and \leftroot translate into shifts by the specified number of "mu" units.

So I think you can simulate the same behavior in KaTeX today using \hspace and \raisebox:

\sqrt[\raisebox{16mu}{\hspace{-2mu}$\scriptstyle\frac1n$}]{1+\frac{\sqrt{2}}{n}}

Here's how that renders, compared to the non-spaced version:

Not exactly what you pasted from MathJax, and neither matches what LaTeX actually renders with \uproot and \leftroot, but it's close: