When something big (a fraction, a sum, an integral...) appears within a pair of parenthesis, one can typically use \left(...\right) to get delimiters large enough to surround the contents. The delimiters are actually often too large: then \bigl(...\bigr), \Bigl(...\Bigr), \biggl(...\biggr), and \Biggl(...\Biggr) are useful. Those delimiters, unfortunately, do not scale when appearing in \scriptsize (in exponents and the like). In that context, a simple (...) may be too small, \left(...\right) too large, and \bigl(...\bigr) too large as well (first three lines below). I tried using \displaystyle to get delimiters of an intermediate size, but I find even that too big (fourth line). What code should I use to get delimiters of a correct size?
The figure is generated by the following code (plus some cropping).
\documentclass{article}
\usepackage{amsmath}
\begin{document}
\[ x^{\sum_{i=1}^{N} (\frac{a_i + 1}{2b_i} + c_i)} \]% too small
\[ x^{\sum_{i=1}^{N} \left(\frac{a_i + 1}{2b_i} + c_i\right)} \]% too big
\[ x^{\sum_{i=1}^{N} \bigl(\frac{a_i + 1}{2b_i} + c_i\bigr)} \]% too big
\newcommand{\normall}[1]{\mathopen{\displaystyle#1}}%
\newcommand{\normalr}[1]{\mathclose{\displaystyle#1}}%
\[ x^{\sum_{i=1}^{N} \normall(\frac{a_i + 1}{2b_i} + c_i\normalr)} \]% a bit big
\end{document}
\Hugeto my MWE to produce the image big enough, but that made the last pair of parentheses be of a good size. Is there a way to make the website rescale graphics when including them, so that the ratios would remain constant?x^...is just a small part of the expressions I need to manipulate. Those expression depend on multiple parameters, and giving names to the many parts of the expressions only scatters the understanding of what is going on, and in particular makes it harder to detect how the expressions depend on the various parameters. Admittedly, if the expression was just this, I would probably give a name to(a_i + 1) / (2b_i) + c_i.