1

I would like to add two underbraces and two sidebraces in the same equation system as shown in the picture attached. I already managed to add the underbraces but the left and right braces are too long. Furthermore, I couldn't add the sidebraces.

enter image description here

My code is:

\documentclass{article} \usepackage{amsmath} \begin{document}
\begin{align}
\left\begin{array}{c c c c c c}
     a_{11} & \cdots & a_{1m} & a_{1(m+1)} & \cdots & a_{1(2m)}  \\
     \vdots & \ddots & \vdots & \vdots & \ddots & \vdots  \\
     a_{n1} & \cdots & a_{nm} & a_{n(m+1)} & \cdots & a_{n(2m)} \\
     \multicolumn{3}{c}{\underbrace{\rule{2cm}{0pt}}_{A_{n}}}
    & \multicolumn{3}{c}{\underbrace{\rule{3.5cm}{0pt}}_{A_{k}}}    
\end{array}\right \times 
\left(\begin{array}{c}
s_{1} \\
\vdots\\
s_{m} \\
s_{m+1} \\
\vdots \\
s_{2m}
\end{array}\right)
= z \end{align} \end{document}

Does anyone know how to do that? Thank you!

  • 1
    Welcome to TeX.SX! Please make your code compilable (if possible), or at least complete it with \documentclass{...}, the required \usepackage's, \begin{document}, and \end{document}. That may seem tedious to you, but think of the extra work it represents for TeX.SX users willing to give you a hand. Help them help you: remove that one hurdle between you and a solution to your problem. – dexteritas Sep 11 '17 at 14:43
  • See this question, tex.stackexchange.com/questions/331506/…, for the side-brace question. – Steven B. Segletes Sep 11 '17 at 14:48
1

I replaced align with equation, since there were no align tabs and only one equation.

\documentclass{article} 
\usepackage{amsmath} 
\usepackage[usestackEOL]{stackengine}
\stackMath
\begin{document}
\begin{equation}
\left(
\vphantom{\begin{array}{c}a\\a\\a\\\end{array}}
\smash{\underbrace{\begin{array}{c c c }
     a_{11} & \cdots & a_{1m}   \\
     \vdots & \ddots & \vdots   \\
     a_{n1} & \cdots & a_{nm} 
\end{array}}_{A_n}}\,\,
\smash{\underbrace{\begin{array}{c c c }
      a_{1(m+1)} & \cdots & a_{1(2m)}  \\
      \vdots & \ddots & \vdots  \\
     a_{n(m+1)} & \cdots & a_{n(2m)}
\end{array}}_{A_k}}
\right) \times 
\left(\begin{array}{c}
s_{1} \\
\vdots\\
s_{m} \\
s_{m+1} \\
\vdots \\
s_{2m}
\end{array}\right)
\setstackgap{L}{1.2\normalbaselineskip}
\vcenter{\hbox{\stackunder[1pt]{%
  \left.{\Centerstack{\\ \\}}\right\}\scriptstyle S_m%
}{
  \left.{\Centerstack{\\ \\}}\right\}\scriptstyle S_k%
}}}
= z \end{equation} 
\end{document}

enter image description here

  • Thank you so much for your help. This is honestly more than I expected! – Marvin Bachmann Sep 11 '17 at 15:56
1

You might do like this:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\[
\underset{
  \underbrace{
    \hphantom{\begin{matrix}a_{1,m} & \cdots & a_{n,m}\end{matrix}}
  }_{\displaystyle A_n}
  \hspace{2\arraycolsep}
  \underbrace{
    \hphantom{\begin{matrix}a_{n+1,m} & \cdots & a_{n+k,m}\end{matrix}}
  }_{\displaystyle A_k}
}{
  \begin{pmatrix}
  a_{1,1} & \cdots & a_{n,1} & a_{n+1,1} & \cdots & a_{n+k,1}  \\
  \vdots  & \ddots & \vdots  & \vdots & \ddots & \vdots  \\
  a_{1,m} & \cdots & a_{n,m} & a_{n+1,m} & \cdots & a_{n+k,m}
  \end{pmatrix}
}
\times 
\begin{pmatrix}
s_{1} \\
\vdots\\
s_{m} \\
s_{m+1} \\
\vdots \\
s_{m+k}
\end{pmatrix}
\hspace{-0.5em}
\begin{matrix}
\left.\begin{matrix}
\vphantom{s_1}\\\vphantom{\vdots}\\\vphantom{s_m}
\end{matrix}\right\rbrace S_m \hfill
\\
\left.\begin{matrix}
\vphantom{s_{m+1}}\\\vphantom{\vdots}\\\vphantom{s_{m+k}}
\end{matrix}\right\rbrace S_k \hfill
\end{matrix}
= z 
\]

\end{document}

enter image description here

However, you should consider a different presentation:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\[
\begin{pmatrix}\vphantom{\bigg|} A_n & A_k \end{pmatrix}
\begin{pmatrix} \vphantom{\bigg|} S_n \\ \vphantom{\bigg|} S_k \end{pmatrix}
=z
\]
where
\begin{align*}
A_n &=
\begin{pmatrix}
  a_{1,1} & \cdots & a_{n,1} \\
  \vdots  & \ddots & \vdots  \\
  a_{1,m} & \cdots & a_{n,m} 
\end{pmatrix}
& S_n &=
\begin{pmatrix}
  s_{1} \\
  \vdots\\
  s_{m}
\end{pmatrix}
\\
A_k &=
\begin{pmatrix}
  a_{n+1,1} & \cdots & a_{n+k,1} \\
  \vdots & \ddots & \vdots  \\
  a_{n+1,m} & \cdots & a_{n+k,m}
\end{pmatrix}
& S_k &=
\begin{pmatrix}
  s_{m+1} \\
  \vdots \\
  s_{m+k}
\end{pmatrix}
\end{align*}

\end{document}

enter image description here

  • oh my god thank you so much for your help! I really appreciate it! Is it possible to ada label like \label{eq:01-A} to your first solution? It seems like latex is just ignoring the label. Thanks again! – Marvin Bachmann Sep 11 '17 at 15:55
  • @MarvinBachmann Use \begin{equation} and \end{equation}, so it will be numbered and will accept a \label. – egreg Sep 11 '17 at 15:58

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