Math & Science ⇒ amsmath | Font Size of Fractions in the »cases« Environment

[Karlo]

Hello,

I am trying to write Bayes theorem, using cases environment in amsmath package.

My code is:

Code: Select all

\begin{equation}
 \pi(\boldsymbol{\theta}\!\mid\!\boldsymbol{x}) =
    \begin{cases}
     	  \frac{q(\boldsymbol{\theta}) r(\boldsymbol{x}\mid\boldsymbol{\theta})}{\int_{\Theta} q(\boldsymbol{\theta}) r(\boldsymbol{x}\mid\boldsymbol{\theta}) \: \emph{d} \lambda(\boldsymbol{\theta})} 
             & \text{if $\int_{\Theta} q(\boldsymbol{\theta}) r(\boldsymbol{x}\!\mid\!\boldsymbol{\theta}) \: \emph{d} \lambda(\boldsymbol{\theta}) \neq 0$} \\ 
             0 & \text{else} 
     \end{cases}
\end{equation}

I have a problem with the size of the fraction in it. It's too small, I'd like to give it more space so that the integral in the fraction is as big as the integral after if. Is there an easy way how to make it happen? Hope it's understandable from my description where my problem is:)

Thanks a lot,

K.

[localghost]

The cases environment of amsmath can be enhanced by several packages.

• cases
• mathtools

Let's take a look at a solution with mathtools because it offers the right stuff here.

Code: Select all

\documentclass{scrartcl}
\usepackage[T1]{fontenc}
\usepackage{mathtools}  % loads »amsmath«

\begin{document}
  \begin{equation}
    \pi(\boldsymbol{\theta}\!\mid\!\boldsymbol{x}) =
    \begin{dcases}
      \frac{q(\boldsymbol{\theta}) r(\boldsymbol{x}\mid\boldsymbol{\theta})}{\displaystyle\int_{\Theta} q(\boldsymbol{\theta}) r(\boldsymbol{x}\mid\boldsymbol{\theta}) \: \emph{d} \lambda(\boldsymbol{\theta})}
      & \text{if $\int_{\Theta} q(\boldsymbol{\theta}) r(\boldsymbol{x}\!\mid\!\boldsymbol{\theta}) \: \emph{d} \lambda(\boldsymbol{\theta}) \neq 0$} \\
      0 & \text{else}
    \end{dcases}
  \end{equation}
\end{document}

What has been done here:

• The cases environment has been replaced by dcases. This activates \displaystyle in the whole environment and thus increases font size for fractions.
• In the denominator of the first fraction it is necessary to enable \displaystyle separately in order to let the integral symbol appear in the familiar size.

Further reading:

• »Math mode«

Best regards and welcome to the board
Thorsten

[Karlo]

Yeah,

that's it.

Thanks again for your help,

K.