[Xy-pic] Vertical alignment in xymatrix

[Alexander Perlis]

--- Ross Moore <ross at ics.mq.edu.au> wrote:
> There are many diagrams for which \xymatrix is not the best
> environment to use.
> 
> The reason \xymatrix is so popular, and usually the first choice
> for things that look like commutative diagrams, is that it has a
> familiar syntax.

Another reason \xymatrix is so popular is that the Xy-pic User's
Guide is devoted to it. I suspect many users read enough of the Guide
to get their work done, and never "graduate" to reading the Reference
Manual or the many nice papers that Ross Moore and Kris Rose have
written (in TUGboat and elsewhere). In short, my guess is that many
users of Xy-pic don't even know that there is such a thing as
\xygraph or an underlying kernel language. In other words, to many
users, Xy-pic and \xygraph are one and the same.

I myself was turned onto \xygraph by the Kris Rose article on
conceptual alignment:

   http://www.diku.dk/forskning/topps/bibliography/1994.html
   http://evarose.net:800/~krisrose/ECCT-94/rose/

Once turned on, I studied the Xy-pic Reference Manual to learn more.
When converting old documents in which diagrams were hacked together
using matrix environments, I usually save time by using \xymatrix.
But for all new diagrams, I use \xygraph. It does everything
\xymatrix does, but also so much more, and gives so much freedom in
how to describe a diagram.

To those readers who haven't used it much, I heartily recommend
checking it out. The key difference between \xymatrix and \xygraph is
"global versus local". With \xygraph, instead of working on a grid
moving from top left to bottom right one row at a time, you instead
give the position of each object relative to some other object. Thus
you can start in the middle of the diagram, or the lower-right,
whatever seems most natural. This is what Kris Rose means when he
says that \xygraph is "conceptual": you specify the pieces of the
diagram in the same order you would write them on a board when
explaining the diagram to a colleague. It's marvelous!

Alex


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