[Xy-pic] Delicate alignment problem.

[Ross Moore]

On Mon, 12 May 2003, Michael Abbott wrote:

> On Mon, 12 May 2003, R.P.I. Lewis wrote:
> > Michael Abbott <michael at araneidae.co.uk> writes:
> > > \[\xygraph{
> > > !{0;/r5cm/:/u1.5cm/::}
> > > *{AAAA}="AA"
> > > [] !{"AA"+R *!L{{}=BBBB},
> > >     *+[F.]\frm{}="BB"}       % <--- ????
> > > [] "AA"[r] *+{CCCC}="CC"
> > > [] "BB" :^-f "CC"
> > > [] !{"CC"+D *!U{\cong},
> > >     +D *+!U{DDDD}="DD"}
> > > "DD" :^-h[d] *+{EEEE}="EE"
> > > :^k[l]{FFFF}="FF" []
> > > !{"AA"*+\frm{}} :_g "FF"
> > > }\]
> > >
> > > The defect is this: the arrow out of BBBB starts too far away from
> > > BBBB. This is because the reference point when "BB" is defined is at
> > > the left, so when I try to expand the enclosing box (with
> > > *+[F.]\frm{}="BB") the expansion is incorrect.
> >
> > Perhaps i am missing the point, but if you move the "BB" to
> >    *!L{{}=BBBB}="BB"
> > Then the arrow starts next to the BBBB just as in your xymatrix below

 What is wrong with using   *+!L{{}=BBBB}="BB"   to get the margin ?

(which is different to  *!L+{{}=BBBB}="BB"  by the way)
Does the extra slight shift to the right upset the diagram ?


Hope this helps,

	Ross

>
> Yes, but that's not what I want: the start of the arrow should leave a
> small gap between itself and the BBBB.  In other words, it should look the
> same as an arrow out of *+{BBBB}.
>
> The problem is that I use the line
>      *+[F.]\frm{}="BB"}       % <--- ????
> to try and pick up the previously set BBBB (with \frm{}) and try to expand
> it (with +), but its base point is in the wrong place (because I needed to
> tuck it up against the AAAA), so the expansion is too much.  (The [F.] is
> just so we can see what's happening.)
>
> I still don't really understand positioning well enough.  Let's try and
> see what's going on here in detail.
>
> Basically I want to set two adjacent boxes (the AAAA and {}=BBBB texts)
> touching side by side; after doing this, I want to pick up the two boxes
> and create *+{} expanded versions of them.  If I can typeset the BBBB box
> in place without having to disturb its origin, or if I can put the origin
> back in the middle afterwards then I'm done.
>
>
> > Here I tried +D*+!U{DDDD}="c"  which appears to work. I am not
> > entirely sure what the !, bit does, but it doesn't seem necessary.
>
> Ouch.  That's perfect.  Thanks very much for spotting that!
>
> Oops.  I've completely forgotten what I was trying to do with the ! --
> it's suppose to "restore the reference point of an object", so it must
> have been a relic of some sort.
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