# Why is there a space between the left parenthesis and the radical sign?

Minimal working example:

\documentclass{article}

\begin{document}
Default spacing: $$(\sqrt 2)$$

Negative space after the left parenthesis: $$(\!\sqrt 2)$$
\end{document}


To me, the default spacing looks bad, and it looks better to remove space after the left parenthesis. Is there any reason not to do so? Why is it the default in the first place?

• I usually add a thin space after a radical, if a parenthesis follows. – egreg Oct 5 '20 at 16:12
• @egreg Just for clarification—you add more space before the right parenthesis to even things out, e.g. (\sqrt 2\,)? – tlou Oct 5 '20 at 16:50
• Not for making things even, but to separate the vinculum from the parentheses. – egreg Oct 5 '20 at 16:54
• TeX performs math typesetting by building up and arranging various (two-dimensional) "boxes". While deciding how to place these boxes vertically and horizontally, TeX generally actually doesn't "know" what's inside the boxes. By having to guard against various worst-case placement outcomes, it can happen from time to time that, for a combination of actual contents, either slightly tighter or slightly looser spacing would be better ex post. Incidentally, I don't share your view as to the optimal placement of round parentheses around \sqrt{2}: I prefer (\sqrt{2}\,) to (\!\sqrt{2})... – Mico Oct 5 '20 at 16:59
• Unfortunately, TeX treats Rad atoms the same as Ord atoms and therefore doesn't insert spacing before (after) a closing (opening) delimiter. The asymmetry of the default radical symbol makes this look a bit odd, as you have reported, but then again, such a situation doesn't occur very often and (\sqrt 2\,) is a feasible workaround for these one-off cases. – Henri Menke Oct 5 '20 at 17:09

It's an optical effect. There is no space added between ( and the surd:

\documentclass{article}

\newcommand{\zw}{\kern-0.05pt\vrule width0.1pt\kern-0.05pt}

\begin{document}

$$(\zw\sqrt{2})$$

$$(\sqrt{2})$$

\end{document}


The fact is that the construction is asymmetric; the effect is less visible with a symmetric symbol such as x:

Instead of reducing the space in front of the radical (in any case \! is too drastic), increase the space after it, particularly if a parenthesis follows.

\documentclass{article}
\usepackage{amsmath}

\begin{document}

$$(\sqrt{2})$$

$$(\sqrt{2}\,)$$

$$(\mspace{-1.5mu}\sqrt{2})$$

\end{document}


• Very nice the sequence of the zoom of the differents pictures. +1 – Sebastiano Oct 5 '20 at 17:57