[Xy-pic] Deficiencies in xymatrix package?

Alexander Perlis alexanderperlis at yahoo.com
Mon May 12 13:29:18 CEST 2003

Regarding \xymatrix, someone wrote:
>> The most serious is that if one node of a horizontal arrow has a
>> superscript and the other a subscript, they will quite obviously
>> appear on different levels.

Michael Abbott replied:
> I quite agree, and I have to say that this "feature" is really
> annoying. I would be very happy if an option to xymatrix could
> be implemented to make centre-line alignment the default option.
> I started a conversation about this in March, but alas Ross said
> that this would be "rather hard" to do.

  As you probably know, it isn't too difficult to solve this problem:
just put \entrymodifiers={+!!<0pt,\fontdimen22\textfont2>} near the
top of your document. Your concern is probably mostly that it ought
to be easy to change the default behavior without having to memorize
that cryptic line above, and perhaps even do so on a
per-\xymatrix-basis without repeating that one-liner throughout the
document. I agree. And so do others.

Vadim Radionov first posted the above solution on 27Jun2001 and
suggested it should be the default behavior. I independently looked
into this around Aug2002 and arrived at the same solution, and wrote
the following TUGboat submission explaining the alignment issues and
how the solution above works:


More importantly to the present discussion, near the end of this
article, I propose specific syntax for giving the user easy access to
this solution, on a per-document or per-diagram basis, both for
\xymatrix and \xygraph. Could you take a look and let me know whether
the proposed syntax would meet your needs?

(I am not implying I have the skills to implement this. I'm trying to
guide the discussion as to what it is we need, with the hope that an
expert like Kris Rose will then say, "oh, is that all? that's easy!
took me half an hour. done." Of course Kris Rose (and Ross Moore)
have already done so much for us, we can hardly expect more, but
unfortunately there may be few other experts sufficiently familiar
with the Xy-pic source code. I tried making changes on various
occasions, none successful, which reminded of being a mere mortal...)

By the way, the cryptic one-line solution from the top of this
message should be well-known by now. In the vigorous March
discussion, Radionov reposted this solution on 5Mar2003, and Ross
Moore made use of that solution in his post of 10Mar2003. I believe
by now we should be in agreement that this is the *right* way to
achieve what I call axis-alignment (you call it centre-alignment),
and so now we are down to the matter of making it easily accessible:
agreeing on what we want (the syntax, and what it does), and hoping
someone will take pity on our needs and implement the proposal! Your
input to that proposal is appreciated.

Alexander Perlis

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