# [Xy-pic] A question

Wynn Stirling wynn at ee.byu.edu
Tue Feb 11 11:15:19 CET 2003

I am a new user of XY-pic and a new subscriber to the users group.  I am
using XY-pic to draw factor graphs, a task for which it appears to be
very well suited.  A distinguishing feature of factor graphs is that
they have two types of nodes---some need to be framed with rectangles,
and some with circles.    These framed structures need to be of
different sizes to accommodate the varryng contents.   The two types of
nodes are then joined by undirected edges.

I have used both xymatrix and xygraph to create these graphs, and  both
give me the same result, so let me describe only what happens when I use
xymatrix:  When I enter the following code

\xymatrix{
&    &   &  *++[F-]{p_{S_1|S_2S_3}^\prime} \\
%
*++[F-]{p_{R_2}p_{R_1|R_2}p_{R_3|R_2}} \ar@{-}[r]
& *[o]++++[F-]{R_1,R_2,R_3} \ar@{-}[r]
&  *++[F-]{p_{S_2|R_1R_3}^\prime} \ar@{-}[r]&
*++++[o][F-]{S_1,S_2,S_3} \ar@{-}[u] \ar@{-}[d] \\
%
&    &   &  *++[F-]{p_{S_3|S_2}^\prime} \\
}}

the lines (arrows) either leave a gap between the rectangles and circles
or they intersect the circles.  I would like to know how to eliminate
the gaps and overshoots, and to force the arrows to touch but not cross
the frames.   I should note that when I do not try to enlarge the
frames, things work just fine.

Wynn

--
Wynn Stirling
Professor, Electrical and Computer Engineering
459 CB Brigham Young University
Provo, UT 84602
(801) 422-7669
wynn at ee.byu.edu