[Xy-pic] Fw: Xy-pic and Qcircuit

[Kristoffer H Rose]

Dear Everyone,

In the message below, Bryan reports that Xy-pic 3.8 has problems with 
diagrams generated from Qcircuit.  Since we have a maintenance release 
coming up (3.8.6 with Daniel's xypdf 1.7), any help with a quick solution 
from anyone who has experienced similar problems would be most welcome!

Bryan and Steve: if you can submit a complete TeX document to the list (as 
.tex and .pdf attachments), which, when typeset, explains and demonstrates 
the problem then that will probably facilitate a solution.

Thanks to all,
        Kris

[1]http://www.cquic.org/Qcircuit/
__
Kristoffer H Rose, ph.d. <krisrose at us.ibm.com> +1(914)784-7642 (fax -6324)
IBM T.J.Watson Research Center, PO Box 704, Yorktown Heights, NY 10598

----- Forwarded by Kristoffer H Rose/Watson/IBM on 03/09/2011 06:51 PM 
-----

Bryan Eastin <beastin at gmail.com> 
03/08/2011 11:33 AM

To
krisrose at tug.org
cc
Steve Flammia <sflammia at gmail.com>
Subject
Xy-pic and Qcircuit






Hi,

I am one of the authors of Qcircuit, a macro package for drawing
quantum circuits used by many researchers working in quantum
computing.  (See, for example, http://arxiv.org/pdf/0710.2560 or
http://arxiv.org/pdf/quant-ph/0504097 .)

Qcircuit is based on Xy-pic version 3.7.  It has been widely used in
the community for about 7 years, but lately I have begun to receive
complaints that it is broken.  I've done some investigating, and it
turns out that some of the changes made this summer to Xy-pic in the
3.8 release have broken Qcircuit.  As users slowly upgrade their LaTeX
distributions, the problems spread.

I've tried to isolate what's going wrong, and I think I've identified
all of the problems (Roughly.  I don't know enough to dig around
inside Xy-pic.).  I'm not sure if these are bugs in the new release or
intentional changes, but I've catalogued the issues at the end of this
email.

If they're bugs then please consider this a bug report and a heartfelt
request for some kind of fix.  If they're not bugs I would be very
grateful for any advice on how I might circumvent these features.

If you're interested in knowing more about Qcircuit, the package has a
webpage at http://www.cquic.org/Qcircuit/ .  I believe it is presently
the most commonly used method for typesetting quantum circuits.

Thank you for your time,
Bryan Eastin

[I have CC'd this email to Steven Flammia, the other author of Qcircuit.]



%The following examples were generated using MikTeX version 2.7 and
Xy-pic version 2.8.5 on a Windows XP machine.  Not all of these
problems
%seem to manifest on machines running TeXLive on Ubuntu or Mac.  Some
variant of the first issue happens on all systems, though an error
%message is not always generated.

%Problem:
%Cannot draw an arrow to an entry of xymatrix of size 0em.
%Qcircuit command broken:
%\Qcircuit
%Example code:
\xymatrix @*[o] @*=<0em> {
& \ar @{-} [0,-1] & \ar @{-} [0,-1]
}
%Resultant error message:
%Xy-pic Warning: division overflow [FixQcircuit:51]
%
%! Arithmetic overflow.
%<recently read> \quotPTK@
%Hack:
%Set the default entry size in \xymatrix to .05em.  Smaller sizes
somehow result in bigger gaps.
%The hack is undesirable because:
%Arrows meeting at an empty entry no longer connect.  Important!

%Problem:
%The \frm command no longer works on null objects.
%Qcircuit command broken:
%\targ
%Example code:
\xy <0em,0em>*+<.8em>\frm{o}\endxy
%Resultant error message:
%None.
%Hack:
%Insert a very tiny object.
%E.g., for \targ, use the code {\xy {<0em,0em> \ar @{ - } +<.39em,0em>
\ar @{ - } -<.39em,0em> \ar @{ - } +<0em,.39em> \ar @{ - }
-<0em,.39em>},<0em,0em>*{\rule{.01em}{.01em}}*+<.8em>\frm{o}\endxy}
%The hack is undesirable because:
%Aside from being inelegant, it requires a change to the original
code, which has already been widely distributed.  Less important.

%Problem:
%Erratic generation of Division Overflow Errors.
%Qcircuit command broken:
%Uncertain.
%Example code:
%The following works.
\xymatrix @*[o] @*=<0.09em> @R=1.7em @C=1em {
& \ar @{-} [1,1]  \ar @{-} [0,-1] & & *{a} \ar @{-} [0,-1] \\
& \ar @{-} [-1,1] \ar @{-} [0,-1] & & *{a} \ar @{-} [0,-1]
}
%The following doesn't work:
\xymatrix @*[o] @*=<0.1em> @R=1.7em @C=1em {
& \ar @{-} [1,1]  \ar @{-} [0,-1] & & *{a} \ar @{-} [0,-1] \\
& \ar @{-} [-1,1] \ar @{-} [0,-1] & & *{a} \ar @{-} [0,-1]
}
%The following works.
\xymatrix @*[o] @*=<0.11em> @R=1.7em @C=1em {
& \ar @{-} [1,1]  \ar @{-} [0,-1] & & *{a} \ar @{-} [0,-1] \\
& \ar @{-} [-1,1] \ar @{-} [0,-1] & & *{a} \ar @{-} [0,-1]
}
%Resultant error message:
%Xy-pic Warning: division overflow [FixQcircuit:82]
%
%! Arithmetic overflow.
%<recently read> \quotPTK@
%Hack:
%Use a different number?
%The hack is undesirable because:
%I have no idea what will work when or whether a workable alternative
will always be available.

%Problem:
%Arrows connect poorly to empty entries in \xymatrix
%Qcircuit command broken:
%\link
%Example code:
\xymatrix @*[o] @*=<0.01em> @R=1.7em @C=1em {
& \ar @{-} [1,1]  \ar @{-} [0,-1] & & \ar @{-} [0,-1] \\
& \ar @{-} [-1,1] \ar @{-} [0,-1] & & \ar @{-} [0,-1]
}
%Resultant error message:
%None.
%Hack:
%Insert a very tiny object.
%E.g.,
\xymatrix @*[o] @*=<0.01em> @R=1.7em @C=1em {
& *{\rule{.01em}{.01em}} \ar @{-} [1,1]  \ar @{-} [0,-1] &
*{\rule{.01em}{.01em}} & \ar @{-} [0,-1] \\
& *{\rule{.01em}{.01em}} \ar @{-} [-1,1] \ar @{-} [0,-1] &
*{\rule{.01em}{.01em}} & \ar @{-} [0,-1]
}
%The hack is undesirable because:
%The connections still don't look quite right.  Moderately important.
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