LaTeX forum ⇒ Math & Science ⇒ Matrix within a matrix

[davefulton]

Hello all,
I am trying to get this array

Code: [Select all] [Expand/Collapse] [Download] (untitled.tex)

\begin{equation}U = \left( \begin{array}{c}
\rho\\
\rho u\\
\rho v\end{array} \right),\end{equation}

into the values marked x in this array

Code: [Select all] [Expand/Collapse] [Download] (untitled.tex)

\[ F^+(U) = \left\{ \begin{array}{ll}
          x & \mbox{$x \geq 0$};\\
          x & \mbox{$x \geq 0$};\\
         -x & \mbox{$x < 0$}.\end{array} \right. \]

so something like

Code: [Select all] [Expand/Collapse] [Download] (untitled.tex)

\[ F^+(U) = \left\{ \begin{array}{ll}
      \begin{equation}U = \left( \begin{array}{c}
      \rho\\
      \rho u\\
      \rho v\end{array} \right),\end{equation}        
      & \mbox{$x \geq 0$};\\
          x & \mbox{$x \geq 0$};\\
         -x & \mbox{$x < 0$}.\end{array} \right. \]

however this won't compile. Any help

[Stefan Kottwitz]

Hi,

it would work without the equation environment:

Code: [Select all] [Expand/Collapse] [Download] (untitled.tex)

\[ F^+(U) = \left\{ \begin{array}{ll}
      U = \left( \begin{array}{c}
      \rho\\
      \rho u\\
      \rho v\end{array} \right),
      & \mbox{$x \geq 0$};\\
          x & \mbox{$x \geq 0$};\\
         -x & \mbox{$x < 0$}.\end{array} \right. \]

Stefan

[php1ic]

As another option, try using the 'cases' environment together with the 'pmatrix' environment provided by the amsmath package.

Code: [Select all] [Expand/Collapse] [Download] (untitled.tex)

\documentclass{article}
 
\usepackage{amsmath}
 
\begin{document}
 
\[
F^+(U) =
   \begin{cases}
\begin{pmatrix}
\rho\\
\rho u\\
\rho v
\end{pmatrix} & \mbox{$x \geq 0$};\\[5ex]
\begin{pmatrix}
\rho\\
\rho u\\
\rho v
\end{pmatrix} & \mbox{$x \geq 0$};\\[5ex]
-\begin{pmatrix}
\rho\\
\rho u\\
\rho v
\end{pmatrix} & \mbox{$x < 0$}
   \end{cases}
\]
 
\end{document}

[davefulton]

Thank you, thank you, thank you x

[localghost]

Now that the problem is solved, please mark the topic accordingly as described in Section 3 of the Board Rules. This applies to all your other requests.


Best regards
Thorsten