[Xy-pic] Controlloing the dimensions of xy boxes

[Luigi Santocanale]

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Hi everybody,

I have several difficulties controlling the dimensions
produced by the environments \xy\endxy.

The following is an example of what I mean (Latex file
follows, dvi-file in attachment). There are two different
graph escapes which are supposed to draw the objects of a
categorical commutative square. However, even if very
similar, they behave in a very different manner. 

Have you got any suggestion ?

Thanks, 

	Luigi

%%% Begin Latex File
\documentclass{article}

\usepackage[all]{xy}

%% Draw a square, 1st attempt

\newgraphescape{s}[8]{
  []*+{#1}="1"
  (
  :@{{}{}{}}[d(#5)r(#6)]*+{#2}="2"
  :@{{}{}{}}[d(#8)r(#7)]*+{#4}="4",
  :@{{}{}{}}[d(#8)r(#7)]*+{#3}="3"
  )
  }

\newgraphescape{S}[6]{
  []!s{#1}{#2}{#3}{#4}{#5}{0}{#6}{0}
  }
\begin{document}

%% Draw a square, 2nd corrected attempt

\newgraphescape{t}[8]{
  []
  :@{{}{}{}}[]*+{#1}="1" %% This line the only difference
  (
  :@{{}{}{}}[d(#5)r(#6)]*+{#2}="2"
  :@{{}{}{}}[d(#8)r(#7)]*+{#4}="4",
  :@{{}{}{}}[d(#8)r(#7)]*+{#3}="3"
  )
  }

\newgraphescape{T}[6]{
  []!t{#1}{#2}{#3}{#4}{#5}{0}{#6}{0}
  }

$$
\fbox{\xy\xygraph{
    []
    !S{a}{b}{c}{d}{1}{-1}
  }\endxy}
\hspace{2em}
\fbox{\xy\xygraph{
    []
    !T{a}{b}{c}{d}{1}{-1}
  }\endxy}
$$

\end{document}

%%% End of Latex File
--
Luigi Santocanale
	
Department of Computer Science, University of Calgary.
Tel: (403) 220-5106, fax:(403) 284-4707.
http://www.cpsc.ucalgary.ca/~luigis/
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