[Xy-pic] arrow shape for relations

[Ross Moore]

On 14/01/2009, at 2:19 AM, Jonas Frey wrote:

> Dear Developers,
>
> I would like to use arrows of shape
> --|-->
> or
> --/-->
> in
> in xymatrix to represent relations and profunctors.
>
> If I read the documentation right, that's not possible with
> \ar@{ },

Of course you can do this:

$$
\xymatrix{ A \ar [r] |*=0@{/} \ar [rd] |*=0@{|}  & B \ar [d] |-*=0@{/}
  \\ C \ar [r] |-*=0@{|}
  & D\oplus D \oplus D \oplus D}
$$


> because arrows are always of the form tail/stem/head and thus we  
> can't put
> anything "in the middle".

Yes; but you can "break" the stem, just as you can with \path ...

> However, in section 23 of the reference manual, I saw an example of  
> the \path
> feature that looked similar.

   ... because an \ar  just uses a different (more convenient ?) syntax
to build a \path .

> I tried to use that, but finally gave up because explanation was  
> too technical
> for me to comprehend, and I decided to ask for help here.
>
> My precise question is:
> How to do a macro for arrows of the shapes given above that I can  
> place in
> \xymatrix, and that behaves similar to
> \ar ?
> Ideally, I would like to use coordinates and put labels in a way  
> similar to
> \ar.

A "break" (using | ) works in a completely analogous
way to placing labels using ^ and _ .

>
> Any hints would be really appreciated!
>
> Regards,
>
> Jonas

Hope this helps,

	Ross

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Ross Moore                                       ross at maths.mq.edu.au
Mathematics Department                           office: E7A-419
Macquarie University                             tel: +61 (0)2 9850 8955
Sydney, Australia  2109                          fax: +61 (0)2 9850 8114
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