[Tex/LaTex] Combining split and rcases

bracketsequations

I have an equation, that is split along multiple lines. All equations should be aligned to the equal sign. All but the first equation form a group.

The following gives almost the expected result (These are two examples I have tried, the difference is the ampersand preceding the rcases-environment):

\documentclass{scrartcl}
\usepackage{amsmath}
\usepackage{mathtools}
\usepackage{bm}

\begin{document}

\begin{equation}
\begin{split}
y &= \Psi_1 \left(\xi_1, \Psi_1^\pm \right) \\
\begin{rcases}
\dot{\xi}_1 &= \Psi_2 \left( \xi_2, \Psi_2^\pm(\xi_1) \right) \\
\dot{\xi}_2 &= \Psi_3 \left( \xi_3, \Psi_3^\pm(\bm{\xi}_2) \right) \\
& \qquad \vdots \\
\dot{\xi}_r &= \Psi_{r+1} \left(v, \Psi_{r+1}^\pm(\bm{\xi}_r) \right) \\
\end{rcases} \dot{\bm{\xi}}= \bm{\Psi}_{r+1}\left(\bm{\xi}_r, v\right)
\end{split}
\end{equation}

\begin{equation}
\begin{split}
y &= \Psi_1 \left(\xi_1, \Psi_1^\pm \right) \\
&\begin{rcases}
\dot{\xi}_1 &= \Psi_2 \left( \xi_2, \Psi_2^\pm(\xi_1) \right) \\
\dot{\xi}_2 &= \Psi_3 \left( \xi_3, \Psi_3^\pm(\bm{\xi}_2) \right) \\
& \qquad \vdots \\
\dot{\xi}_r &= \Psi_{r+1} \left(v, \Psi_{r+1}^\pm(\bm{\xi}_r) \right) \\
\end{rcases} \dot{\bm{\xi}}= \bm{\Psi}_{r+1}\left(\bm{\xi}_r, v\right)
\end{split}
\end{equation}

\end{document}

This produces the following output:
Output: Equations are not aligned

But the first equation (y=…) is not aligned with the others. How do I get it aligned?

Best Answer

I wasn't sure if you want the = in the first row to align with the inner group or the outer equals, so this shows both forms:

enter image description here

\documentclass{scrartcl}
\usepackage{amsmath}
\usepackage{mathtools}
\usepackage{bm}

\begin{document}


\begin{equation}
\begin{split}
y &= \Psi_1 \left(\xi_1, \Psi_1^\pm \right)\\
\begin{rcases}
\dot{\xi}_1 &= \Psi_2 \left( \xi_2, \Psi_2^\pm(\xi_1) \right) \\
\dot{\xi}_2 &= \Psi_3 \left( \xi_3, \Psi_3^\pm(\bm{\xi}_2) \right) \\
& \qquad \vdots \\
\dot{\xi}_r &= \Psi_{r+1} \left(v, \Psi_{r+1}^\pm(\bm{\xi}_r) \right) \\
\end{rcases} \dot{\bm{\xi}}&= \bm{\Psi}_{r+1}\left(\bm{\xi}_r, v\right)
\end{split}
\end{equation}


\hrule

\vspace{15pt}
\begin{equation}
\begin{split}
\begin{rcases}
\noalign{\vskip-20pt}
y &= \Psi_1 \left(\xi_1, \Psi_1^\pm \right)\\
\noalign{\vskip5pt}
\dot{\xi}_1 &= \Psi_2 \left( \xi_2, \Psi_2^\pm(\xi_1) \right) \\
\dot{\xi}_2 &= \Psi_3 \left( \xi_3, \Psi_3^\pm(\bm{\xi}_2) \right) \\
& \qquad \vdots \\
\dot{\xi}_r &= \Psi_{r+1} \left(v, \Psi_{r+1}^\pm(\bm{\xi}_r) \right) \\
\end{rcases} \dot{\bm{\xi}}&= \bm{\Psi}_{r+1}\left(\bm{\xi}_r, v\right)
\end{split}
\end{equation}

\end{document}
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