\bigl and \bigr in sub/superscripts

Question

When typesetting expressions with multiple adjacent parentheses, I like to use \bigl and \bigr on the outermost parentheses to make it easier to read, especially with 3 or more parentheses in a row. Unfortunately, this doesn't work in sub/superscripts: the resulting parentheses are huge (relative to the enclosed text) instead of slightly bigger than normal. Is there a substitute for \bigl and \bigr which can be used in this case?

The simplest example of the kind of thing I use this for is \bigl(f(x) + g(x)\bigr). In particular, \left and \right aren't really what I'm looking for.

Answer 1

This is a halfway answer, because it only takes care of the font used in subscripts, not of the height the delimiters have to cope with.

\documentclass{scrartcl}
\usepackage{mathtools,lmodern}

\makeatletter
\def\bBigg@#1#2{{\mathpalette{\bBigg@aux{#1}{#2}}\relax}}
\def\bBigg@aux#1#2#3%
  {\@mathmeasure\z@{\nulldelimiterspace\z@}%
     {#3\left#2\vcenter to#1\big@size{}\right.}%
   \box\z@}
\makeatother


\begin{document}

\[
  x^{\bigl(f(x) + g(x)\bigr)}
\]

\end{document}

(I hope I did it right.)

EDIT

Here's another idea which also scales the height down when in a sub- or superscript so the parenthesis are not that big. Still, this is a messy answer (I just looked at the definition and changed a bit of things).

With this code

\makeatletter
\def\bBigg@#1#2{{\mathpalette{\bBigg@aux{#1}{#2}}\relax}}
\def\bBigg@aux#1#2#3%
  {\@mathmeasure\z@{\nulldelimiterspace\z@}%
     {#3%
       \setlength\dimen@{\dimexpr#1\big@size
         \ifx\scriptscriptstyle#3*26/50\fi
         \ifx\scriptstyle#3*34/50\fi
        \relax}
       \left#2\vcenter to\dimen@{}\right.}%
   \box\z@}
\makeatother

here's a comparison with \scriptstyle and \scriptscriptstyle with the original definition of \big.

Answer 2

The \vstretch macro of the scalerel package is like a \scalebox{1}[]{}, except it works inside math mode and preserves the current math style. Thus, one can define \bigs, \bigrs, etc. to take advantage of this feature.

I have currently set the stretch values to 1.15 and 1.3, but you can change to suit. In the left \parbox, I show it operating automatically in \textstyle, \scriptstyle, as well as \scriptscriptstyle.

In the right \parbox, I use even bigger sizes, to demonstrate two things: 1) one can incorporate both \vstretch and \hstretch into the enlarged glyph; and 2) for double-height constructs, such as around a \frac, the size of the "big" might need to change depending on the math style, since the \frac itself changes the math style of its contents.

\documentclass{article}
\usepackage{scalerel}
\def\bigs#1{\vstretch{1.15}{#1}}
\def\bigrs#1{\vstretch{1.3}{#1}}
\def\biggs#1{\vstretch{1.45}{\mkern-1mu\hstretch{1.3}{#1}\mkern-1mu}}
\def\biggrs#1{\vstretch{1.6}{\mkern-1mu\hstretch{1.5}{#1}\mkern-1mu}}
\def\Biggrs#1{\vstretch{1.75}{\mkern-1mu\hstretch{1.6}{#1}\mkern-1mu}}
\begin{document}
\parbox[b]{1in}{\parskip 1ex
$x^{\bigrs(x + \bigs(x(x+3)\bigs)\bigrs)}$\par
      $\bigs(f(x) + g(x)\bigs)$ \par
   $x^{\bigs(f(x) + g(x)\bigs)}$ \par
$y_{x^{\bigs(f(x) + g(x)\bigs)}}$ \par
}
\parbox[b]{1in}{\parskip 1ex
$       \biggs(\frac{\bigs(f(x) + g(x)\bigs)}{2}\biggs)$ \par
$   x^{\biggrs(\frac{\bigs(f(x) + g(x)\bigs)}{2}\biggrs)}$ \par
$y_{x^{\Biggrs(\frac{\bigs(f(x) + g(x)\bigs)}{2}\Biggrs)}}$ \par
}
\end{document}