In the following beamer frame, I want the description text to stay top-left, while the xymatrix-figure should be centered. However, whatever I tried with \centering, \begin{center} and other online found solution, I've always gotten the diagram aligned left.
\begin{frame}
\frametitle{Butterfly network}
Some text
\begin{figure}[b]
\begin{center}
\begin{displaymath}
\xymatrix@R=0.9pc@C=3.5pc{
S_1 \ar@{.>}[rd] \ar@{.>}[ddd] & & S_2 \ar@{.>}[ld] \ar@{.>}[ddd] \\
& A_1 \ar@{.>}[d] & \\
& A_2 \ar@{.>}[ld] \ar@{.>}[rd] & \\
R_2 & & R_1 \\
}
\end{displaymath}
\end{center}
\end{figure}
\end{frame}
PS I'm quite new to LaTeX, explanation why this solution doesn't work would be very welcome.
EDIT: Wrapping \xymatrix inside \centerline has made the diagram appear almost in the middle, a little to far right...
PSS Running TexLive 2013 on OpenSuSe 13.1