alignat
I found this program and I was wondering how can I add on a left brace as in the systeme package or in the cases environment? Also is it possible to left align the right-hand side of the equal sign ?
\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{alignat*}{4}
2x & {}+{} & y & {}+{} & 3z & {}={} & 10 \\
x & {}+{} & y & {}+{} & z & {}={} & 6 \\
x & {}+{} & 3y & {}+{} & 2z & {}={} & 13
\end{alignat*}
\end{document}
I'd use a simple array environment:
\documentclass{article}
\usepackage{amsmath}
\begin{document}
\[\arraycolsep=1.4pt\def\arraystretch{1.3}
\begin{array}{rcr p{1cm} rcr}
12a + 4b + c &=& -3 && 12a + 2b &=& 0 \\
-27a - 6b - c &=& 0 && -15a - 2b &=& -3 \\
\cline{1-3} \cline{5-7}
-15a - 2b \phantom{\,-\,c\,} &=& -3 & & -3a \phantom{\,-\,2b\,} &=& -3 \\
& & && a &=& -1
\end{array}
\]
\end{document}
For the arrow you can define two nodes with TikZ or PSTricks.
I propose one of these layouts, with the drcases environment from mathtools:
\documentclass{article}
\usepackage{mathtools}
\begin{document}
\begin{align*} \psi^\star \mathcal{H} \; \psi = i \smash[b]{\sum_{h=(1,1,1)}^{(M,N,Z)}} ( &\\[-3.75ex]
& \! \begin{drcases}
A1 \quad AAAAAAAAAA2 & A3 \\
B1 \quad BBBBBBBBBB2 & B3 \\
C1 \quad CCCCCCCCCC2 & C3 \\
D1 \quad DDDDDDDDDD2 & D3 ).
\end{drcases}\delta(\alpha-1)
\end{align*}
where I want to place a curly bracket to right of the last 4 lines and put the expression $\delta(\alpha-1)$ on the right of the bracket-tip.
\begin{align*} \psi^\star \mathcal{H} \; \psi = i \sum_{\mathclap{h=(1,1,1)}}^{\mathclap{(M,N,Z)}} \,( \enspace \begin{drcases}
A1 \quad AAAAAAAAAA2 & A3 \\
B1 \quad BBBBBBBBBB2 & B3 \\
C1 \quad CCCCCCCCCC2 & C3 \\
D1 \quad DDDDDDDDDD2 & D3 ).
\end{drcases}\delta(\alpha-1)
\end{align*}
\end{document}
Best Answer
The
\begin{alignat*}{4}[left = \empheqlbrace]solution which you employ in your own answer requires hand-editing "& 6" to "& 6\phantom{0}" in order to generate the appearance of left-alignment in the final column.If that's too tedious and/or error-prone, do also consider the
\systeme- andarray-based solutions shown below.Note that the three solutions produce the exact same output. In the end, then, your decision should be based mainly on the convenience of the input process. In my opinion, the input convenience of the
systememethod is hard to beat. For sheer flexibility, though, thearray-based method must be tops; however, its input overhead does exceed that of thesystemeapproach (and is roughly on par with theempheqappoach).