xy diagram: set height of a specific row

Question

I'm using the xy package. In the diagram

$$\xymatrix@R=8mm@C=8mm{  & 1\ar@{-}[ddl]\ar@{-}[dr] &  \\
                          & & c\ar@{-}[dd]\\
                        a & & \\
                          & & b\\
                          & 0\ar@{-}[uul]\ar@{-}[ur] &  \\}$$

,

how can I set the row height between c and a and between a and b to be smaller. I want to create this diagram:

\\[2mm] doesn't make any change, and \xymatrix@R=8mm@C=8mm{... only makes global changes.

Answer 1

I've never used xymatrix, and couldn't find anything useful in the manual, after a little searching, but I can provide a TikZ-solution.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{matrix}
\begin{document}
\begin{tikzpicture}
\matrix (thing) [matrix of math nodes,row sep=15pt] {
  &[1cm] 1 &[0.5cm] \\
  &        & c      \\[-15pt]
a &        &        \\[-15pt]
  &        & b      \\
  & 0      &        \\
};
\draw (thing-1-2) -- (thing-2-3) -- (thing-4-3) -- (thing-5-2);
\draw (thing-1-2) -- (thing-3-1) -- (thing-5-2);
\end{tikzpicture}
\end{document}

Answer 2

This is the best that I could do with Xy-pic. The idea is to make the c and b special (off-matrix) targets à la Section 3.3 of xyguide.pdf.

\documentclass{article}
\usepackage[matrix,arrow]{xy}
\begin{document}
\[\xymatrix @R=12mm @C=8mm {
& 1\ar@{-}[dl] 
& \save[]+<0mm,-8mm>*{c} \ar@{-}[l] \restore  \\
                            a & 
& \save[]+<0mm,-8mm>*{d} \ar@{-}[ld] \ar@{-}+<0mm,12mm> \restore  \\
                              & 0\ar@{-}[ul] &  \\}\]
\end{document}

The fact that you got two good TikZ answers in the time that it took to get one bad Xy-pic answer indicates the ease of crafting TikZ code. If you're still persuadable I would encourage you to learn TikZ.

Answer 3

Just add rows and close up them:

\xymatrix@R=2mm@C=8mm{
& 1 \ar@{-}[dddl] \ar@{-}[ddr] \\
\\
&& c \ar@{-}[dd] \\
a \ar@{-}[dddr] \\
&& b \ar@{-}[ddl] \\
\\
& 0
}

Answer 4

In the relation to the comment of of Leon:

{tikz} is certainly an option

I would suggest something like this:

\documentclass{article}
\usepackage{amsmath}
\usepackage{tikz}
\usetikzlibrary{calc,matrix}
\usepackage[all]{xy}
\begin{document}
\[\xymatrix@R=8mm@C=8mm{  & 1\ar@{-}[ddl]\ar@{-}[dr] &  \\
                          & & c\ar@{-}[dd]\\
                        a & & \\
                          & & b\\
                          & 0\ar@{-}[uul]\ar@{-}[ur] &  \\}\]

\[
\begin{tikzpicture}[baseline,remember picture,]
\matrix (n) [matrix of math nodes,%
                 column sep=8mm,
                 row sep=8mm,nodes={anchor=center},]
{
  & 1 &  \\
  &   & c\\
a &   &  \\[-4mm]
  &   & b\\[-4mm]
  & 0 &  \\
};
\draw (n-1-2) -- (n-3-1);
\draw (n-1-2) -- (n-2-3);
\draw (n-3-1) -- (n-5-2);
\draw (n-4-3) -- (n-5-2);
\draw (n-4-3) -- (n-2-3);
\end{tikzpicture}
\]


\end{document}

Answer 5

Here is a pstricks solution to drawing this diagram. It uses pst-node to identify node locations/connections and multido to iterate over the nodes, arranged in a circle of radius 2cm:

\documentclass{article}
\usepackage{pst-node}% http://ctan.org/pkg/pst-node
\usepackage{multido}% http://ctan.org/pkg/multido
\begin{document}
\begin{pspicture}(10,10)
  \SpecialCoor% Enable polar coordinates (r;t)
  \newcommand{\radius}{2cm}% Radius of diagram
  \psset{linestyle=solid,linewidth=0.5pt,linecolor=black,nodesep=10pt}% Edge parameters
  \rput{180}{%
    \degrees[5]% 5 angles per revolution (each angle is 360/5=72 degrees)
    \pnode(\radius;0){node-0}% Root note
    \multido{\iA=0+1,\iB=1+1}{5}{%
      \pnode(\radius;\iB){node-\iB}% Node
      \pcline(node-\iA)(node-\iB)% Edge
    }
  }

  % Labels
  \rput{0}(node-0){$a$}%
  \rput{0}(node-1){$0$}%
  \rput{0}(node-2){$b$}%
  \rput{0}(node-3){$c$}%
  \rput{0}(node-4){$1$}%
\end{pspicture}
\end{document}