alignamsmathbracescasesequations
Is there an intelligent way to left-align the parts right of & of the two cases environments shown below (if x >= 0, otherwise, if y < 0, otherwise). I wonder if there is a better way than using manual spaces:
\begin{align*}
u(x) &=
\begin{cases}
0 & \text{if } x \geq 0 \\
1 & \text{otherwise}
\end{cases}
\\
\tau &=
\begin{cases}
a+b+c+d & \text{if } y < 0 \\
1 & \text{otherwise}
\end{cases}
\end{align*}
I would definitely go the second way with $\displaystyle: I find that it looks strange to have something centered after a bullet. To get the vertical alignment correct, just add [t] after \begin{aligned}, where "t" means "top". (See also the top of page 8 of the User's guide for the amsmath Package.)
Another solution (and numbering) with the empheq package (which loads mathtools, which loads amsmath):
\documentclass{article}
\usepackage[a4paper,margin=2.5cm]{geometry} % set page parameters
\usepackage{amsfonts, % for \mathbb and \mathcal macros
empheq}%
\numberwithin{equation}{subsection}
\setcounter{section}{1}
\setcounter{subsection}{1}
\begin{document}
\begin{subequations}
\begin{empheq}[left={\mathbb{E}(X)=\displaystyle\int_{-\infty}^{\infty} x\,dF(x)=\empheqlbrace}]{alignat = 2}
& \sum_{x \in \mathcal{X}} xf_{X}(x) =\sum_{x \in \mathcal{X}} x\mathbb{P}(X=x)
&\qquad & \text{if $X$ is discrete}, \\
& \int_{-\infty}^{\infty} xf_{X}(x)\,dx
& &\text{if $X$ is continuous}. \end{empheq}
\end{subequations}
\begin{subequations}
\begin{empheq}[left={\mathbb{E}(X)=\displaystyle∫_{-∞}^{∞} x\,dF(x)=\empheqlbrace}]{flalign}
& ∑_{x ∈ \mathcal{X}} xf_{X}(x) =∑_{x ∈ \mathcal{X}} x\mathbb{P}(X=x)
& &\text{if $X$ is discrete},&\hspace{5em} & \\
& ∫_{-∞}^{∞} xf_{X}(x)\,dx
&& \text{if $X$ is continuous}. \end{empheq}
\end{subequations}
\end{document}
Best Answer
You can use the solutions to an earlier question, just exchanging the order of the statements.
Another solution is to use the
mathtoolspackage and use something like\mathrlap0\hphantom{a+b+c+d}in place of your 0.