Centering a xy matrix inside beamer frame and figure

Question

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

Answer 1

I don't know, what the problem is for you, but as you do not provide a complete MWE, I can only do as you requested. The matrix is centred. I reduced the code a little bit.

% arara: pdflatex

\documentclass{beamer}
\usepackage[all]{xypic}

\begin{document}
\begin{frame}
  \frametitle{Butterfly network}
  Some text
      \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{frame}
\end{document}

If you are still having problems, you may try the tikz-cd package instead. Maybe, this is working for you.

% arara: pdflatex

\documentclass{beamer}
\usepackage{tikz-cd}

\begin{document}
\begin{frame}[fragile]
\frametitle{Butterfly network}
Some text
    \[
    \begin{tikzcd}[row sep=small]
    S_1 \ar[dotted]{rd} \ar[dotted]{ddd} & & S_2 \ar[dotted]{ld} \ar[dotted]{ddd} \\
    & A_1 \ar[dotted]{d} & \\
    & A_2 \ar[dotted]{ld} \ar[dotted]{rd} & \\
    R_2 & & R_1
    \end{tikzcd}
    \]
\end{frame}
\end{document}