[Xy-pic] spacing objects and arrows using xymatrix

[Philip Hirschhorn]

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].

Hope this helps,
Phil Hirschhorn