# Specific alignment within \begin{align} environment

I would like to produce the following alignment with \begin{align*}...\end{align*}.

   -0,1 <  E  < 0,1
6,3 <  S  < 6,4
6,3-0,1 < S+E < 6,4+0,1
6,2 <  I  < 6,5


I can't figure out where to place the & signs. Thanks for your help.

With array:

\documentclass{article}
\usepackage{amsmath,array}

\begin{document}

\begin{equation*}
\renewcommand{\arraystretch}{1.2} % like in cases
\setlength{\arraycolsep}{0pt} % use math spacings
\begin{array}{ r<{{}} c >{{}}l }
-0{,}1   < &  E  & < 0{,}1 \\
6{,}3   < &  S  & < 6{,}4 \\
6{,}3-0{,}1 < & S+E & < 6{,}4+0{,}1 \\
6{,}2   < &  I  & < 6{,}5
\end{array}
\end{equation*}

\end{document}


\documentclass{article}
\usepackage{amsmath}

\begin{document}

alignat:
\begin{alignat}{2}
-0,1 &< E &&< 0,1 \\
6,3 &< S &&< 6,4 \\
6,3-0,1 &<S+E&&< 6,4+0,1 \\
-0,1 &< I &&< 6,5
\end{alignat}
\end{document}

• I'm curious: why does it need &&? – muxoveji May 23 at 10:47
• @muxoveji all ams alignments alternate between right and left alignment as if \begin{array}{rlrlrlrlrlrlrlrlrlrl} and you have no new entries to the left of the second < so that column is empty. (put x in between the & to see what I mean.) – David Carlisle May 23 at 10:54
• That makes sense! Thanks a lot for the explanation! – muxoveji May 23 at 10:55

align family environments, by nature, produce right/left alignments of successive columns. Thus they are not easily adapted to achieve the center-alignment of the middle column that was requested.

Also, in order to not treat the comma as punctuation, one can either enclose each comma in its own braces {,} (yuck!), or use the \cmac macro provided to use active commas to fix the problem...Just make sure you don't use commas in another context while \cmac is active.

With tabstackengine...

\documentclass{article}
\usepackage{tabstackengine}
\let\svcm,
{
\catcode,=\active %
\gdef,{{\svcm}}
}
\newcommand\cmac{\catcode,=\active }
\TABstackMath
\begin{document}
$\TABbinary \cmac \setstacktabulargap{0pt} \tabularCenterstack{rcl}{ -0,1 <& E &< 0,1 \\ 6,3 <& S &< 6,4 \\ 6,3-0,1 <&S+E&< 6,4+0,1 \\ 6,2 <& I &< 6,5}$
\end{document}


If one wants more vertical spacing between the lines, simply add \setstackgap{L}{1.2\baselineskip} to the mix:

Another solution with the eqparbox package:

\documentclass{article}
\usepackage{amsmath}
\usepackage{eqparbox}
\newcommand{\eqmathbox}[2][M]{\eqmakebox[#1]{$\displaystyle#2$}}

\begin{document}

\begin{align*}
-0{,}1 &< \eqmathbox{E} < 0{,}1 \\
6{,}3 &< \eqmathbox{S} < 6{,}4 \\
6{,}3-0{,}1 & <\eqmathbox{S+E} < 6{,}4+0{,}1 \\
6{,}2 & < \eqmathbox{I} < 6{,}5
\end{align*}

\end{document}