[Tex/LaTex] How to make an equation more compact

equationsspacing

I have an equation that wastes a lot of space around the union symbol:

\documentclass{article}

\usepackage[cmex10]{amsmath}
\usepackage{amssymb}

\begin{document}
\begin{equation}
RA_U  \left ( new , ref \right ) =
\bigcup_{
  \left\{ 
    i  \text{ such that }  f_i \left(  ref \right) < f_i \left( new \right) 
  \right\} 
}
\left\{ 
  X \in \mathbb{R}^M ; 
  x_i \in \left [ f_i \left(  ref \right) ; f_i \left( new \right) \right ] 
\right\}
\end{equation}
\end{document}

enter image description here

This is especially dreadful, since I am using IEEEtran.cls, which has two columns.

How can I compress the equation around the union symbol?

Best Answer

You can use \mathclap from mathtools package:

\documentclass{article}

\usepackage[cmex10]{amsmath}
\usepackage{amssymb}
\usepackage{mathtools}

\begin{document}
\begin{equation}
RA_U  ( \mathit{new}, \mathit{ref} ) =
\bigcup_{\mathclap{
  \left\{
    i  \text{ such that }  f_i (\mathit{ref}) < f_i ( \mathit{new} )
  \right\}
}}
\left\{
  X \in \mathbb{R}^M ;
  x_i \in [ f_i ( \mathit{ref} ) ; f_i ( \mathit{new} ) ]
\right\}
\end{equation}
\end{document}

Output:

enter image description here

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