[Xy-pic] spacing objects and arrows using xymatrix

[Ross Moore]

Hello Philip and Alberto,

On 17/10/2011, at 10:47 AM, Philip Hirschhorn wrote:

> On Sun, 16 Oct 2011, Alberto Alcalá Alvarez wrote:
> 
>> hello, I'm trying to get the following done, using the xymatrix
>> command: I have a diagram with a >>--->> arrow going down, but the
>> tail of the arrow, >>, gets overlapped with the name of the origin
>> of the arrow, so my question is if there is a way to save some space
>> between the name of the origin and the tail of the arrow, or if I
>> could rescale the shaft of the arrow in order to make it
>> shorter. thanks a lot!
> 
> Instead of having the arrow start from the current node, you could
> specify both the starting point and the target of the arrow, and set
> the starting point to a little bit below the current node.  That is,
> try the following:
> 
> \begin{displaymath}
>  \xymatrix{
>    {A} \ar@{>>->>}[]+<0ex,-2ex>;[d]
>    & {C} \ar@{>>->>}[d]\\
>    {B}
>    & {D}
>  }
> \end{displaymath}
> 
> The downward arrow on the right is as you describe, but the downward
> arrow on the left
> 
>  \ar@{>>->>}[]+<0ex,-2ex>;[d]
> 
> begins at []+<0ex,-2ex> (which is 2ex below the current node) and aims
> at [d].

Another solution is to define a new directional.

\newdir{ >>}{{}*!/-2.6667\jot/\dir{>>}}

viz.

\begin{displaymath}
\UseTips % for AMS-style arrowheads
 \xymatrix{
   {A} \ar@{>>->>}[]+<0ex,-2ex>;[d]
   & {C} \ar@{{ >>}->>}[d]
   & E  \ar@{>>->>}[d] \\
   {B}
   & {D} & F
 }
\end{displaymath}

Together with using AMS-style arrowheads,
you get the middle example in the attached image.

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Note that a lot of the {...}  are actually redundant
in that example coding.

> 
> Hope this helps,
> Phil Hirschhorn


Hope this helps,

	Ross

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Ross Moore                                       ross.moore at 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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