Aligning equations while using cases in align environment
The \Centerstack
retains a settable but fixed baselineskip. Thus, using \Centerstack
s to set both the equations of the case, as well as (separately) the conditions of the case, will insure that their baselineskips are compatible.
\documentclass{report}
\usepackage{amsmath}
\usepackage[usestackEOL]{stackengine}
\stackMath
\setstackgap{L}{1.2\normalbaselineskip}
\begin{document}
\begin{align}
& a+b+c+d+e+f = 15000 && \text{for } a = 1 ... 15 \\
& D_t= \left\{\Centerstack[l]{\text{equation} ,\\ \text{another equation}}\right.&&
\Centerstack{ \text{for } t = 1 ... 10 \\ \text{for } t = 1 ... 10}
\end{align}
\end{document}
Here are two ways to obtain it:
\documentclass{article}
\usepackage{mathtools}
\begin{document}
\begin{alignat}{2}
& a+b+c+d+e+f = 15000 &\quad & \text{for } a = 1 ... 15 \\
& D_t=
\begin{cases}
\text{equation} , \\
\text{another equation} ,
\end{cases} & & \begin{aligned}
\text{for } t = 1 ... 10 \\\text{for } t = 1 ... 10
\end{aligned}
\end{alignat}
\begin{alignat}{2}
& a+b+c+d+e+f = 15000 &\quad & \text{for } a = 1 ... 15 \\
& D_t=
\mathrlap{\begin{cases}
\text{equation} , & \text{for } t = 1 ... 10 \\
\text{another equation} ,\hspace{1.9em}& \text{for }t = 1 ... 10
\end{cases}}
\end{alignat}
\end{document}