# 2 left alignments under cases

I would like to align something under cases as follows:

value1                    if condition
value2  line1ofvalue2...  otherwise
line2ofvalue2..
line3ofvalue2.


First, there are only 2 conditions (each one for one value), so I want if condition and otherwise are left adjusted. Then as my value2 is a long, I need to split it into 3 lines, so I want these 3 lines to be left adjusted.

Does anyone know how to do this? Thank you very much

-

The array environment provides a very similar layout and typesetting to the amsmath package cases environment. In fact, amsmath defines cases exactly as an array with some stretch (an \arraystretch of 1.2) and a specific column alignment (@{}ll@{}). Consider the following minimal example displaying the two different styles:

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\noindent Original \texttt{cases} example:
$X=% \begin{cases} 0& \text{if r-j is odd},\\ r!\,(-1)^{(r-j)/2}& \text{if r-j is even}. \end{cases}$

\noindent Using the \texttt{array} environment:
$\renewcommand{\arraystretch}{1.2}% X=\left\{% \begin{array}{@{}ll@{}} 0& \text{if r-j is odd},\\ r!\,(-1)^{(r-j)/2}& \text{if r-j is even}. \end{array} \right.$
\end{document}


Therefore, using the array environment, one could attempt:

\documentclass{article}
\usepackage{amsmath}
\begin{document}

\noindent Requested environment using \texttt{array}:
$\renewcommand{\arraystretch}{1.2}% X=\left\{% \begin{array}{@{}lll@{}} 0& & \text{if r-j is odd},\\ k& +7& \text{if r-j is even}. \\ & +1+2i& \\ & \binom{3}{n} \end{array} \right.$
\end{document}​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​


The gap between the first two left-aligned columns can also be adjusted (using @{}l@{}ll@{}, say) if needed. The advantage of this approach is flexibility in terms of the array environment, while still retaining the visual equivalence with the cases environment; that is, a user-defined cases environment.

-
Thanks for your comment, what is the use of % in the \left\{%? –  SoftTimur Aug 9 '11 at 2:37
I almost use it out of habit, but it's best to read the short and long answer to this here: What is the use of percent signs at the end of lines –  Werner Aug 9 '11 at 2:44

Here's an extension of the amsmath cases environment. There's a new optional argument for customizing the cases columns. Without argument, it work like the original cases.

\makeatletter
\let\@ifnextchar\new@ifnextchar
\left\lbrace
\def\arraystretch{1.2}%
\array{#1}%
}
\makeatother


The original definition in amsmath.sty contains @{}l@{\quad}l@{}, which we replaced by #1. Now you can use all features of array column specifications.

Complete example with usage:

\documentclass{article}
\usepackage{amsmath}
\makeatletter
\let\@ifnextchar\new@ifnextchar
\left\lbrace
\def\arraystretch{1.2}%
\array{#1}%
}
\makeatother
\begin{document}
$\begin{cases} value1 & if condition \\ value2 & otherwise \end{cases}$
$\begin{cases}[@{}lp{3cm}l@{}] value1 & & if condition \\ value2 & line1ofvalue2 \newline line2ofvalue2 \newline line3ofvalue2 & otherwise \end{cases}$
\end{document}

-

Is this what you are looking for?

\documentclass{article}
\usepackage[fleqn]{amsmath}
\begin{document}
\newcommand{\Phantom}{\phantom{value2}}%
\begin{align*}
f(x) = \begin{cases}
value1& condition1 \\
value2 \text{ line1ofvalue2}& condition2\\
\Phantom \text{ line2ofvalue2}\\
\Phantom \text{ line3ofvalue2}
\end{cases}
\end{align*}
\end{document}

-