I use
\begin{align}
\label{blah}
...
\end{align}
in order to do equations of multiple lines. Unfortunately the equation number (coming from label{blah}) is not centered vertically in the middle of the multiple lines. How to do this with align ?
alignenvironment: How many are there? An even or odd number of lines? Should there be a single equation number for all lines in thealignstructure, or are there groups of equations. Posting an MWE (minimum working example) would be really helpful. – Mico Mar 20 '13 at 23:33