Two column align environment with one line spanning both columns

Question

Is there a good/correct way of making an align environment with one line spanning multiple columns?

At the moment I'm using a hack like the following, but I feel that it's probably not the best way.

\documentclass{article}
\usepackage{amsmath}

\begin{document}
\begin{align}
 L1C1 &= 1234 \,,&     L1C2 &= abcd \,,\\
 L2C1 &= 1234 \,,&     L2C2 &= efgh \,,\\
 L3 &= 1234567890abcdefghijklmnop \ . \hspace{-30cm}
\end{align}    
\end{document}

Answer 1

this is also a hack, but it will give the desired result.

use \rlap to "hide" the width of the overlong line. for the example given, i would do this for the last line:

L3 &= 1234567890\rlap{$abcdefghijklmnop \ .$}

you might even want to put some extra space after that to get the desired separation; just look at the output to see what's needed.

most lines of math contain reasonable places where one can break without damage.

Answer 2

To span you could use \span:

\documentclass{article}
\usepackage{amsmath}

\begin{document}
\begin{align}
 L1C1 &= 1234 \,,&     L1C2 &= abcd \,,\\
 L2C1 &= 1234 \,,&     L2C2 &= efgh \,,\\
 L3 &= {}\span\omit$1234567890abcdefghijklmnop$\ .\hidewidth
\end{align}    
\end{document}

It turned out to be a lot more hacky than I initially thought it would be.