Vertical alignment using cases

Question

Using the following code, one gets the $X$ vertically aligned with the "center" of the cases. Is there a way to vertically align the $X$ with the $0$ in this output?

\documentclass{article}
\usepackage{amsmath}

\begin{document}
  \begin{equation}
    X=
    \begin{cases}
      0, & \text{if}\ a=1 \\
      1, & \text{otherwise}
    \end{cases}
  \end{equation}
\end{document}

@Zarko: It wouldn´t be symmetric. The pointy part would be towards the upper side in front of the equal sign. — Ramiro de la Vega, Aug 26 '16 at 19:58
This is can be only drawn with tikz or pstrick packages ... and as all answer says: don't doing this, result is ugly. — Zarko, Aug 26 '16 at 20:07
@Zarko: When one has many cases and this is at the beginning of a question (in an exam say), having the equal sign centered is uglier, because it looks like the brace invades the previous question. — Ramiro de la Vega, Aug 26 '16 at 20:10

score 3 · Answer 1 · answered Aug 26 '16 at 19:59

3

Since cases is basically a matrix environment, a \begin{matrix} X\\ \end{matrix} should align this entry.

But it does not look nice! Don't do this!

\documentclass{article}
\usepackage{amsmath}

\begin{document}
  \begin{equation}
    \begin{matrix} X = \\
      \\
      \end{matrix}  
    \begin{cases}
      0, & \text{if}\ a=1 \\
      1, & \text{otherwise}
    \end{cases}
  \end{equation}


  \begin{equation}
    \begin{matrix} X  \\
      \\
    \end{matrix}  =
    \begin{cases}
      0, & \text{if}\ a=1 \\
      1, & \text{otherwise}
    \end{cases}
  \end{equation}


\end{document}

answered Aug 26 '16 at 19:59

Thanks Christian, the first alternative would look good if the pointy part of the brace was also aligned with the equal sign. Is this possible? – Ramiro de la Vega Aug 26 '16 at 20:03
@RamirodelaVega: Huh??? The pointy part of the brace is centered -- it can't be centered any longer if you want to force that to be aligned with the = as well and the 0 as well. – Aug 26 '16 at 20:05
I guess the brace would need to be different, it would not have the "pointy part" in the center. – Ramiro de la Vega Aug 26 '16 at 20:08
1

@RamirodelaVega: That's what I said -- it's asymmetric. No, that's not nice – Aug 26 '16 at 20:09

score 3 · Accepted Answer · edited Apr 13 '17 at 12:35

You can, but the result is very dubious.*

\documentclass{article}
\usepackage{amsmath}
\usepackage{delarray}

\begin{document}

\begin{equation}
\renewcommand{\arraystretch}{1.2}
X=\begin{array}[t]\{{@{}l@{\quad}l@{}}.
  0, & \text{if $a=1$} \\
  1, & \text{otherwise}
\end{array}
\end{equation}

\begin{equation}
X=\begin{cases}
  0, & \text{if $a=1$} \\
  1, & \text{otherwise}
\end{cases}
\end{equation}

\end{document}

_{* Big understatement; actually I believe it is completely wrong. Making the brace asymmetric would be even worse. See A curly brace with an asymmetric cusp for this, I refuse to even think about it. ;-)}

Thanks for the link @egreg, that´s closer to what I want, whether it´s popular or not :) — Ramiro de la Vega, Aug 26 '16 at 20:13

Bernard · Answer 3 · 2016-08-26T22:12:43.250

3

It looks nicer with a bracket. Here is a simple way to do it with the empheq package:

\documentclass{article}
\usepackage{empheq}

\begin{document}

  \begin{empheq}[left ={\begin{gathered}X=\\ ~\end{gathered}\empheqlbrack}]{gather} 
\begin{alignedat}[t]{2}
       & 0, &\quad & \text{if}\ a=1 \\
       & 1, & & \text{otherwise}
    \end{alignedat}
  \end{empheq}

\end{document}

edited Aug 26 '16 at 22:12

answered Aug 26 '16 at 20:56

Bernard

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Vertical alignment using cases

3 Answers3