[Xy-pic] distance betwen double arriws

[Michael Barr]

If you use diagxy (or the barr option in the latest version of xy), the 
problem does not seem to arise.  Or you can use the arrow offset feature 
to place the arrows separately.

Michael

On Wed, 19 Mar 2014, xy-pic-request at tug.org wrote:

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>   1. Re: double arrows (Ross Moore)
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> ----------------------------------------------------------------------
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> Message: 1
> Date: Thu, 20 Mar 2014 06:53:59 +1100
> From: Ross Moore <ross.moore at mq.edu.au>
> To: Davide Sangiorgi <Davide.Sangiorgi at cs.unibo.it>
> Cc: "xy-pic at tug.org list" <xy-pic at tug.org>
> Subject: Re: [Xy-pic] double arrows
> Message-ID: <BB70F58F-528C-475A-8D6E-DACC5043CC1E at mq.edu.au>
> Content-Type: text/plain; charset="us-ascii"
>
> Hi Davide,
>
> On 20/03/2014, at 12:18 AM, Davide Sangiorgi wrote:
>
>> Dear Ross:
>> Putting postive numbers does not seem to help:
>> now the shortening of the line and the dots go at the other end of the lines.  Thanks.  If you happen to find out something, i'd be very interested (i use weak arrows a lot in my talks)
>
> Here is a way to do it; but there is a catch.
>
>
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> \ar @<2pt>@{-}@*{[|(4)]}[d(.68)]
> \ar @<-2pt>@{-}@*{[|(4)]}[d(.68)]
> \ar @2@{{}>}@*{[|(4)]}[d]
>
> That number (.68) needs to be found by trial and error.
> It is the fraction of the distance to the matrix position
> of the cell [d] from the target.
> It will be different for different diagrams if you adjust the
> row spacing, and different for longer arrows connecting cells
> further apart, etc.
>
> But if you use it a lot, some numbers with become quite common
> for you.
> In practice, you can pass it as an argument to a macro
> e.g. with argument pattern
>    \dblar[#1](#2)
>   ---> \ar @<2pt>@{-}@*{[|(4)]}[#1(#2)] etc.
>
>
>> Best regards,
>> DS
>
>
> Hope this helps,
>
> 	Ross
>
> ------------------------------------------------------------------------
> Ross Moore                                       ross.moore at mq.edu.au
> Mathematics Department                           office: E7A-206
> Macquarie University                             tel: +61 (0)2 9850 8955
> Sydney, Australia  2109                          fax: +61 (0)2 9850 8114
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