[OS X TeX] diagonal arrows in figures

Ross Moore ross at ics.mq.edu.au
Wed Apr 20 06:07:00 EDT 2005

Hi Philipp,

On 20/04/2005, at 7:16 PM, Philipp Mathey wrote:

> On 19-Apr-05, at 11:05 PM, Ross Moore wrote:
>> There are 2 ways to get better diagrams when using XYpic with pdftex .
>> A.
>> One way is to load the  xypdftex  driver-support file:
>>      \usepackage[pdftex,all,....]{xy}
>> B.
>>       \usepackage[ps,dvips,all,....]{xy}
>> ---------------------------------------------------------------------- 
>> --
> What is the fastest way to use xypic ?

That depends a lot on what you are doing.

> I noticed it takes a lot of time to load up xymatrices.
> (even when using "\CompileMatrices").

Yes. That is because \xymatrix is not very efficient.
Rather, people tend to use it in situations where it works,
but is not necessarily the most appropriate construction for
the kind of diagram that needs to be set.

Often \xygraph  will produce a similar result much more quickly.
But there the high-level language is rather more abstract,
so less familiar --- hence seems to be harder, at first sight.

But whichever Xy-pic feature you use, it will always be fastest
to create an image from each diagram, then just reuse this image
on later runs, rather than reinterpret every diagram each time.

For this, you want the same kind of strategy as what  pdftricks
provides, or  ps4pdf .

Learn how to use these, and your documents containing Xy-pic diagrams
will compile much, much faster --- on all but the first run after
some change has been made to a diagram.

> I have always just used the "all" option, never pdftex, or ps, dvips ..
> From what you wrote, I assume that adding pdftex, for example, to the  
> options would create visually more appealing results but would also  
> possibly slow xypic down a little  ?

More appealing, yes.
Slower --- in fact, no!
Using the PostScript back-end is generally *much* faster.

In non-ps mode, Xy-pic works by laying font-characters adjacent
to each other, e.g. to build a line segment at an arbitrary angle.
The position of each piece needs to be calculated and stored in the
  .dvi (or .pdf ) file.

In ps mode, a line segment is just a pair of points (start and finish).
An appropriate \special command is created and written to the  .dvi  
This requires *much* less computational time for the TeX engine.

The downside of using  ps  mode is that not all TeX viewers can show
the results.  It needs  dvips (or other driver)  and a PostScript
interpreter such as Ghostscript  (or Adobe's Distiller) before the
results can be seen.

Note that this is *not* encapsulated ps (.eps), so there's no
guarantee that a non-PostScript-based  .dvi viewer can show the
embedded PostScript bits --- even something like  xdvi  can get
confused with the complexity of the final document.

> Or is the difference ( of time of compilation) negligible ?

Not negligible at all.
Using the  'ps' and 'dvips'  leads to both speed-ups and
better quality output!

Combine this with  ps4pdf  (or  pdftricks)  and the first time
you include a new diagram, or alter an existing one in your document,
it will be quite slow, but thereafter it should be *much* faster.

build new diagrams separately, within a different document having  
nothing else.
When you are sure it is complete, then include it in your main job.

Of course as computers get faster and faster, then you don't really
notice the slow-downs due to the diagrams.

Hope this helps,

	Ross Moore

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Ross Moore                                         ross at maths.mq.edu.au
Mathematics Department                             office: E7A-419
Macquarie University                               tel: +61 +2 9850 8955
Sydney, Australia                                  fax: +61 +2 9850 8114

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