4

The following, I believe, is a strange behavior of \bigl(<math content>\bigr) in inline math mode and in the align environment. Consider the following MWE:

enter image description here

\documentclass[letterpaper]{article}
\usepackage{amsmath,amssymb,mathtools}
\usepackage{fourier}
\begin{document}
Consider having an exponential expression raised to another power; for instance, $\bigl(a^2\bigr)^4$. Using the definition of $a^n$,
    \begin{align*}
    \bigl(a^2\bigr)^4 &= \bigl(a^2\bigr)\bigl(a^2\bigr)\bigl(a^2\bigr)\bigl(a^2\bigr) && \text{Here the base is $\bigl(a^2\bigr)$}\\
    &=\underbrace{(a\cdot a)(a \cdot a)(a \cdot a)(a \cdot a)}_{\text{$2 \cdot 4$ or 8  factors}}\\
    &=a^8
    \end{align*}
\end{document}

The difference is obvious if you zoom in. For example:

enter image description hereenter image description here

Note the parenthesis are of different heights. I suppose its due to the definition of the commands \bigl and \bigr. Can any one shed some insight into the matter. I know several users here prefer using the above rather than \left to \right so am refraining from these commands. I would also like a fix to the size of the parenthesis.

EDIT

It seems that the exponent, "superscript", is the one to blame here for its behaviour in the modes \textstyle and \displaystyle.

  • I don't see the “obvious difference”, the right one is just a little bit down, isn't it? Here you can see the definition of \big. By the way, what role does \left and \right play here? – Manuel May 13 '14 at 19:04
  • 1
    I think it has something to do with "cramped" mathstyles. – Steven B. Segletes May 13 '14 at 19:10
  • @Manuel That's the difference. It's not that obvious but weird. – azetina May 13 '14 at 19:11
  • See for example, tex.stackexchange.com/questions/145306/… regarding cramped styles or else tex.stackexchange.com/questions/154474/… – Steven B. Segletes May 13 '14 at 19:16
  • @StevenB.Segletes - The present case is actually not related to cramped vs uncramped setting of superscripts within one and the same math style, say \textstyle; rather, it arises because the amount by which the superscript is raised above the baseline is greater when \displaystyle is in effect (as is the case in an align environment) than when \textstyle is in effect. – Mico May 13 '14 at 20:22
6

The brackets are the same size, but the superscripts 2 and 4 are lower in inline math than in display style

  • @azetina you only need it once per alignment cell not in each factor, you could locally do \let\displaystyle\relax if you wanted an alignment in textstyle – David Carlisle May 13 '14 at 20:49

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