Math & Science ⇒ number an align conglomerate on the left

[madablasan]

Hi all,
I have a question about alignment of equation numbers, this is my code:

Code: Select all

\documentclass{book}
\usepackage{amsmath}
\begin{document}
\begin{align}
\max \qquad &\sum_{v}d(A,B)v(F_{1},F_{2},A,B)&&\label{problem}\tag{P}\\
\text{s.t.}\qquad & \displaystyle\sum_{\substack{v:i\in F_{1},\\j\in
B}}v(F_{1},F_{2},A,B)\leq c_{ij}&&\text{for every
$i\in\mathcal{F},j\in\mathcal{C}$}\label{constraint1}\\
&\sum_{v:i\in F_{2}}u_{i}(A,B)v(F_{1},F_{2},A,B)\leq
f_{i}&&\text{for every $i\in\mathcal{F}$}\label{constraint2}\\
&v\geq 0.&&\nonumber
\end{align} 
\end{document}

Essentially, I have 4 lines within an align environment, two of which I want numbered (constraint1 and constraint2). Besides that, I would like to number the whole system on the left. Since I didn't find a way to do that, right now I tagged the first line as (P), but I couldn't find a way to move that (P) to the left side in the center.

I know \reqno and \leqno let you number all equations either on the right or on the left, but I don't know how to number a single equation (or align, or array conglomerate) on the left and everything else on the right.

Thanks!

[Stefan Kottwitz]

Hi,

welcome to the board!

You could use parbox or minipage environments or tabular for placing a tag on the left side, such as:

Code: Select all

\parbox{.05\textwidth}{(P)}%
\parbox{.95\textwidth}{%
  \begin{align}
  ...
  \end{align}}

Just a remark: if tags are commonly on the right side, I would not place a single tag on the left. Numbering or tags, respectively, are intended for look-up when cross-referenced, so the reader should know there's a consistent place to look for. Just one exceptional tag on a left side looks more like a design idea, not like a real and useful tag - just my opinion.

Stefan

[madablasan]

Ok, that worked great, thanks! I put the (P) as a tag/label inside an empty align on the left box so that it could be accessible through hyperref.
About the style, I think you're right, but it's common practice in my field to do it this way. I will bring it up with my supervisor, he suggested the tag on the left in the first place.