3

Minimal working example:

\documentclass{article}

\usepackage{amsmath, amssymb}

\begin{document}

$$\left| \bigcup_{\substack{V \subseteq C_m \\ V \supsetneq U}} \mathcal{B}_V \right|$$

\end{document}

gives

enter image description here

which looks imbalanced as the vertical lines are much longer at the top than the bottom. How can I tweak this to make it look nicer?

Changing the \left and \right to \Big gives the following, but it's also not great:

enter image description here

Changing to \left\vert and \right\vert (as per here) is also poor:

enter image description here

5

Please observe \Bigl ... \Bigr, not \Big ... \Big pair and \[ ... \], not $$ ... $$. You can choose more convenient vertical dimension from the suggested ones, however your second example looks pretty good.

\documentclass{article}

\usepackage{amsmath, amssymb}

\begin{document}

%    $$\left| 
\[
\Bigl\biggl\Biggl|\bigcup_{\substack{V \subseteq C_m \\ V \supsetneq U}} \mathcal{B}_V 
\Bigr\biggr\Biggr|
\]
%\right|$$

\end{document}
  • Thank you! \Biggl| and \Biggr| is my favourite, so I'll use that. – Rebecca J. Stones Apr 3 '17 at 12:02
5

Delimiters are not required to cover the whole subformula, so \bigg or \Bigg might do:

\documentclass{article}

\usepackage{amsmath, amssymb}
\usepackage{mathtools} % for \DeclarePairedDelimiter

\DeclarePairedDelimiter{\abs}{\lvert}{\rvert}

\begin{document}

Wrong:
\[
\left| \bigcup_{\substack{V \subseteq C_m \\ V \supsetneq U}} \mathcal{B}_V \right|
\]
Possibly right:
\[
\biggl| \bigcup_{\substack{V \subseteq C_m \\ V \supsetneq U}} \mathcal{B}_V \biggr|
\qquad
\Biggl| \bigcup_{\substack{V \subseteq C_m \\ V \supsetneq U}} \mathcal{B}_V \Biggr|
\]
Easier
\[
\abs[\bigg]{\bigcup_{\substack{V \subseteq C_m \\ V \supsetneq U}} \mathcal{B}_V}
\qquad
\abs[\Bigg]{\bigcup_{\substack{V \subseteq C_m \\ V \supsetneq U}} \mathcal{B}_V}
\]
Overkill:
\[
\raisebox{-1.5ex}{%
  $\abs[\Bigg]{%
    \raisebox{1.5ex}{%
      $\displaystyle\bigcup_{\substack{V \subseteq C_m \\ V \supsetneq U}} \mathcal{B}_V$%
    }%
  }$%
}
=3
\]
\end{document}

Take your pick. I wouldn't choose the last one; personally, I'd go with \bigg.

enter image description here

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