Centered text and Equations aligned

Question

I want to write something like a table with states and the corresponding equations but the equations are supposed to be aligned, as seen in the picture.

Unfortunately I haven't found a solution yet. I already tried align but then the text isn't centered. That's the code I tried:

\begin{align*}
\textit{State} && \textit{Rate leave} &= \textit{rate enter} \\
(0,0) && \lambda P_{0,0} &= \sum\limits_{n=1}^{\infty} \mu_n P_{0,n} \\
(0,n), n > 0 && (\lambda + \mu_n)P_{0,n} &= \sum\limits_{m=1}^{\infty} \mu_m P_{n,m} \\
(m,n), mn > 0 && (\lambda + \mu_n)P_{m,n} &= \lambda P_{m-1,n}
\end{align*}

Has anybody an idea what I should use to get the text centered?

Answer 1

I'd use an array too, but I simplify the header by removing qquad and inserting @{{}={}} instead. Also, I add \renewcommand{\arraystretch}{1.3} for better line spacing. And I agree with @Sebastiano that using text is better.

\documentclass{article}
\usepackage{amsmath}    
\begin{document}

\[ 
\renewcommand{\arraystretch}{1.3}
\begin{array} {c r @{{}={}} l}
\text{State}   & \text{Rate leave}             & \text{rate enter}                 \\ 
(0,0)          & \lambda P_{0,0}               & \sum_{n=1}^{\infty} \mu_n P_{0,n} \\ 
(0,n),\ n > 0  & (\lambda + \mu_n)P_{0,n}      & \sum_{m=1}^{\infty} \mu_m P_{n,m} \\ 
(m,n),\ mn > 0 & \quad(\lambda + \mu_n)P_{m,n} & \lambda P_{m-1,n}
\end{array}
\]

\end{document}

Answer 2

Use array, with a small trick to get the spacing right (no, the correct spacing is not \,).

\documentclass{article}
\usepackage{amsmath,array}

\begin{document}

\begin{equation*}
\begin{array}{@{}  c @{\qquad} r @{} >{{}}l @{}}
\textit{State}     & \textit{Rate leave}      &= \textit{rate enter} \\[1ex]
(0,0)              & \lambda P_{0,0}          &= \sum_{n=1}^{\infty} \mu_n P_{0,n} \\[1ex]
(0,n),\ n > 0  & (\lambda + \mu_n)P_{0,n} &= \sum_{m=1}^{\infty} \mu_m P_{n,m} \\[1ex]
(m,n),\ mn > 0 & (\lambda + \mu_n)P_{m,n} &= \lambda P_{m-1,n}
\end{array}
\end{equation*}

\end{document}

I'd avoid \limits, that will unbalance the whole thing.

Answer 3

Another solution, with a gathered and an aligned environments, together with a couple of \vphantom{\sum...}:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\[
\begin{gathered}[t]
\textit{State} \\
\vphantom{\sum\nolimits_{n=1}^{\infty}}(0,0)\\
\vphantom{\sum\nolimits_{n=1}^{\infty}}(0,n), n > 0 \\
(m,n), mn > 0
\end{gathered}
\hspace{4em}
\begin{aligned}[t]
\textit{Rate leave} &= \textit{rate enter} \\
\lambda P_{0,0} &= \sum\nolimits_{n=1}^{\infty} \mu_n P_{0,n} \\
 (\lambda + \mu_n)P_{0,n} &= \sum\nolimits_{m=1}^{\infty} \mu_m P_{n,m} \\
\lambda + \mu_n)P_{m,n} &= \lambda P_{m-1,n}
\end{aligned}
 \]
 \vskip 4ex
\[
\begin{gathered}[t]
\textit{State} \\
\vphantom{\sum_{n=1}^{\infty}}(0,0)\\
\vphantom{\sum_{n=1}^{\infty}}(0,n), n > 0 \\
(m,n), mn > 0
\end{gathered}
\hspace{4em}
\begin{aligned}[t]
\textit{Rate leave} &= \textit{rate enter} \\
\lambda P_{0,0} &= \sum_{n=1}^{\infty} \mu_n P_{0,n} \\
 (\lambda + \mu_n)P_{0,n} &= \sum_{m=1}^{\infty} \mu_m P_{n,m} \\
\lambda + \mu_n)P_{m,n} &= \lambda P_{m-1,n}
\end{aligned}
 \]

\end{document} 

Answer 4

Welcome! A simple array might do.

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\[\begin{array}{cc@{}r@{\,}@{\,}l}
\textit{State} && \textit{Rate leave} &= \textit{rate enter} \\
(0,0) && \lambda P_{0,0} &= \sum\limits_{n=1}^{\infty} \mu_n P_{0,n} \\
(0,n), n > 0 && (\lambda + \mu_n)P_{0,n} &= \sum\limits_{m=1}^{\infty} \mu_m P_{n,m} \\
(m,n), mn > 0 &\quad& (\lambda + \mu_n)P_{m,n} &= \lambda P_{m-1,n}\\
\end{array}\]
\end{document}

Answer 5

If you want to stick to align, eqparbox's \eqmakebox[<tag>][<align>]{<stuff>} aligns all <stuff> with the same <tag> in the centre. You can change the <align>ment to be left, centre (default) or right.

\documentclass{article}

\usepackage{amsmath,eqparbox}

\begin{document}

\begin{align*}
  \eqmakebox[LHS]{  \textit{State} } &&        \textit{Rate leave} &= \textit{rate enter} \\[1ex]
  \eqmakebox[LHS]{$     (0, 0)    $} &&           \lambda P_{0, 0} &= \textstyle\sum_{n = 1}^\infty \mu_n P_{0, n} \\
  \eqmakebox[LHS]{$ (0, n), n > 0 $} && (\lambda + \mu_n) P_{0, n} &= \textstyle\sum_{m = 1}^\infty \mu_m P_{n, m} \\
  \eqmakebox[LHS]{$(m, n), m n > 0$} && (\lambda + \mu_n) P_{m, n} &= \lambda P_{m - 1, n}
\end{align*}

\end{document}

Since eqparbox's macros uses the auxiliary file to store maximum widths related to a <tag>, you'll have to compile at least twice with every change in the contents of <stuff>.