# How to format multiple equations properly?

When I specify a set of partial differential equations, I usually have to write out not only the equation itself, but also its domain. To complete the problem, I need to specify the boundary conditions underneath it in the same fashion. So the information I need to write is of the format:

EQUATIONS in DOMAIN
CONDITIONS in BOUNDARY

Using simple $...$ format, it looks absolutely horrible. So I tried using a 2x2 array using \begin{array}{cc}...\end{array}, but this doesn't look correct either. What is the standard approach to formatting these equations?

Update: This is what I have coded thus far:

 $\begin{array}{cc} -\nabla^2u=0, & \Omega\\u=g & \partial\Omega \end{array}$

-
Could you provide a MWE (minimal working example) of what you have done? –  azetina Dec 11 '12 at 20:35
take a look at the multi-line display structures in amsmath -- texdoc amsmath should bring up the manual if you're working with a tex live installation. –  barbara beeton Dec 11 '12 at 20:35
@azetina: good point! I just updated my question with the code. –  Paul Dec 11 '12 at 20:39
@barbarabeeton \OT In my MikTeX installation (Win 7) I have to command texdoc amsldoc (as the documentation is named amsldoc.pdf). \endOT –  Qrrbrbirlbel Dec 11 '12 at 20:51
@Qrrbrbirlbel -- ah, okay. i'm working on a (shared) linux installation (don't know which flavor of the os), and both amsmath and amsldoc pull up the same manual. but you're right -- it's more reliable to use the exact name. –  barbara beeton Dec 11 '12 at 20:57

You can probably use the align environment:

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{align*}
\end{align*}

\begin{alignat*}{2}
u&=g &      &\partial\Omega
\end{alignat*}
\end{document}


For further reading about alignment, check amsldoc under Displayed equations. About \quad, it is defined as:

\def\quad{\hskip 1em\relax}

-
Yes! This was exactly what I was looking for! Thank you so much, azetina! –  Paul Dec 11 '12 at 20:49
Out of curiousity... What exactly does the command \quad do? –  Paul Dec 11 '12 at 20:50
@Paul \quad is a space command equivalent to 1em –  azetina Dec 11 '12 at 20:54
Using alignat might be a better choice. This just happened to work great only because the right hand side were of approximately equal width. –  Peter Grill Dec 11 '12 at 23:14
I know @PeterGrill It was not my intention to align vertically. It just happened to be. I will update my example with alignat. –  azetina Dec 11 '12 at 23:16