Math & Science ⇒ Numbering in nested align(ed) environments

[voorneveld]

How can I get an equation number for the third line in the following MWE, where I nest align(ed) environments?

Code: Select all

\documentclass{article}
\usepackage{amsmath}

\begin{document}
\begin{align}
\text{maximize } & \text{long expression} \\
\text{with } & \begin{aligned}[t]
a & \in A \\
b & \in B
\end{aligned}
\end{align}
\end{document}

[Stefan Kottwitz]

Hi,

in case different alignment in the rows, I would use two separate align environments instead of nesting.

If it should be one environment though, I would choose the alignat environment which allows several alignment points. A long expression could be "made small" regarding alignment or overlapping alignment points, using \rlap or \clap, which produce a box of width 0 and contained text overlapping to the right or to the left.

Here's an example, where I use many alignment points and column separators, actually in 3 columns:

Code: Select all

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{alignat}{3}
  \text{maximize } &&& \text{\rlap{long expression}} \\
  \text{with } &&&& a & \in A \\
  &&&& b & \in B
\end{alignat}
\end{document}

Also alignat is explained in the amsmath user's guide. In short: the mandatory argument contains the number of alignment columns, and the & mark both alignment points (right and left aligned as in align) and column separation, alternating.

alignat.png (8.06 KiB) Viewed 6036 times

Stefan