\middle too big

Question

I'm trying to typeset an equation that contains a "|":

\begin{align*}
\lambda_{l} = \lim_{q \to 0^{+}}P\left(X_{2} \leq F_{2}^{(-1)}(q) \middle|  X_{1} \leq F_{1}^{(-1)}(q) \right) 
\end{align*}

which gives me

The "|" seems to be too long. I've tried \midbut that makes the vertical bar too short in relation to the outer left and right brackets. Is there a way I can get the "right" size "|" automatically?

Thanks!

Answer 1

I'd argue that not only the middle vertical bar but also the outer parentheses are unnecessarily large. Try using \bigl(, \bigm|, and \bigr) to control the size of the symbols. As an extra nice touch, you could add a thinspace on either side of the big parentheses.

\documentclass{article}
\usepackage[bitstream-charter]{mathdesign}
\begin{document}
\[
\lambda_{l} = \lim_{q \to 0^{+}}P\bigl(\, X_{2} \leq F_{2}^{(-1)}(q) \bigm|  
    X_{1} \leq F_{1}^{(-1)}(q) \,\bigr) 
\]
\end{document}

Answer 2

use \big| instead. However, for me it looks ok with \middle|.

Answer 3

You can use this definition for conditional probabilities, adapted from the last version of mathtools (p. 27 of the doc). It has a simple syntax: \Prob{A \given B} for a a series \left…\middle…\right, or with an optional size argument: \prob[\big-Big-bigg-Bigg]{A \given B}:

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{fourier}
\usepackage{mathtools}

\DeclarePairedDelimiterXPP\prob[1]{P}(){}{
\newcommand\given{\nonscript\:\delimsize\vert\nonscript\:}
#1}
\def\Prob{\prob*}

\begin{document}


\begin{align*}
    \lambda_{l} & = \lim_{q \to 0^{+}}\Prob{X_{2} \leq F_{2}^{(-1)}(q) \given X_{1} \leq F_{1}^{(-1)}(q)} \\
     & = \lim_{q \to 0^{+}}\prob[\big]{X_{2} \leq F_{2}^{(-1)}(q) \given X_{1} \leq F_{1}^{(-1)}(q)}
  \end{align*}
    \end{document}