casesvertical alignment
I have a piecewise function with three "parts." I would like to have all three conditions aligned at the variable x. How do I achieve that? Here is the code I have so far:
\[
f(x) = \begin{cases}
mx^2 +nx +1, & x \le -1 \\
2m e^{|x|-1} + \sin \pi x - 3n, & -1 < x < 1 \\
3x^2 - (m+n)x, & x \ge 1
\end{cases}
\]
It is fairly elementary to align both equations, as well as their variable domains, when defining your own "cases environment" via an array:
\documentclass{article}
\usepackage{amsmath}% http://ctan.org/pkg/amsmath
\begin{document}
\begin{align*}
T_{\text{in general}}\left(n\right) &= aT\left(\frac{n}{b}\right) + n^{c}, && a\geq 1, b\geq 1, c>0 \\
& && a>b^{c} \\
T_{\text{cases}}\left(n\right) &=
\smash{\left\{\begin{array}{@{}l@{}}
\Theta\left(n^{\log_{b}a}\right) \\[\jot]
\Theta\left(n^{c}\log_{b}n\right) \\[\jot]
\Theta\left(n^{c}\right)
\end{array}\right.} && a=b^{c} \\
& && a<b^{c}
\end{align*}
\end{document}
Some minor alignment adjustments were made (like using additional & alignment specifiers), as well as \smashing the "cases environment" and adding the [\jot] line skip. \smash removed any vertical height from it's argument, while \jot is a specific 3pt skip provided by LaTeX.
From a typesetting point of view, note the use of \text{...} in the subscripts. This macro is offered by amsmath and allows text to be typeset in the regular way, while still adjusting for the relative size of the font depending on the placement.
A trick from mathmode (In my version (2.47) it is in section 65.1 on page 113): save the longest left hand side in a box, and then output the left hand sides in a box of that length:
\documentclass[12pt]{scrartcl}
\usepackage{enumitem}
\usepackage{amsmath,amssymb}
\begin{document}
\newsavebox\lW
\sbox\lW{$\nu(A \leftrightarrow B)$}
\begin{enumerate}[noitemsep,label=\alph*)]
\item $\displaystyle\makebox[\wd\lW][r]{$\nu(A\wedge B)$} = \begin{cases}
1,&\text{if $\nu(A) = \nu(B) = 1$};\\
0,&\text{otherwise.}\end{cases}$
\item $\displaystyle\makebox[\wd\lW][r]{$\nu(A \vee B)$} = \begin{cases}
1,&\text{if $\nu(A) = 1$ or $\nu(B) = 1$};\\
0,&\text{otherwise.}\end{cases}$
\item $\displaystyle\makebox[\wd\lW][r]{$\nu(A \rightarrow B)$} = \begin{cases}
1,&\text{if $\nu(A) = 0$ or $\nu(B) = 1$};\\
0,&\text{otherwise.}\end{cases}$
\item $\displaystyle\makebox[\wd\lW][r]{$\nu(A \leftrightarrow B)$} = \begin{cases}
1,&\text{if $\nu(A) = \nu(B)$};\\
0,&\text{otherwise.}\end{cases}$
\item $\displaystyle\makebox[\wd\lW][r]{$\nu(\forall xA)$} = \begin{cases}
1,&\text{if for all $d \in D, \nu(A_x(c_d)) =1$;}\\
0,&\text{otherwise.}
\end{cases}$
\item $\displaystyle\makebox[\wd\lW][r]{$\nu(\exists xA)$} = \begin{cases}
1,&\text{if for some $d \in D, \nu(A_x(c_d)) =1$;}\\
0,&\text{otherwise.}
\end{cases}$
\end{enumerate}
\end{document}
Output
Best Answer
A different solution, which extends the
casesenvironment. It adds an optional argument for defining array column options. The standardcasesbehavior is the default, so without optional argument it's like the normal amsmath's cases.