# [Xy-pic] colored crvs splines

Ross Moore ross at ics.mq.edu.au
Mon Jan 16 02:09:59 CET 2006

Hello Ishanu,

On 16/01/2006, at 9:56 AM, Ishanu Chattopadhyay wrote:

>  that solves my problem, yes.... i always suspected it would be
> THAT simple given the brilliantly absolute simplicity of XY...
> A million thanks to Ross Moore.................
>
> one more question (again, probably obvious to everybody....)
>
> The curved arrow tips dont get "curved" in the right direction...
> My solution was to typeset the arrows and their tips separately...

The arrow-tips should be getting the direction of the tangent
at the end of the curve. However, this doesn't always look best,
since (i) the default tips are quite narrow,
and (ii) this means that any curvature tends to make the
incoming stem too close to one side or the other.

So, the practical problem is to determine what *is* the best
direction for the arrow-tips.

Alternatively, and this is my recommended solution, ...

... switch the style of the arrow-tips to become more 'open',
at least on the ends of curves.

The  cmtip  extension module (via  xycmtip.tex ) provides the
coding needed to do this. There are examples of how to use it
in the Xy-pic Reference Manual.

>
> \xy 0;/r.23pc/: (0,15)*+[o][F-]{q_{1}};
> (10,0)*+[o][F-]{q_{2}};
> {\ar@{-}@[red]@/^1pc/^{\txt{$\sigma_k$}}(2,14)*{};(10,2)*{}};

> {\ar@{>}@[red](10.25,3)*{};(10,2)*{}};

Firstly, you don't need to set the complete arrow again.

Since the first use of \ar  should have setup the current
<connection>  you can just go to the end to drop the tip
where it meets the edge of the object, using:

?-(1)*@{>}

> \endxy
> Is there a better way to do this ?

This can be modified slightly, using an <object-modifier>
to adjust the angle of the tip.
I think an example is in the Ref Manual, perhaps in the
section on "knots" where the large curvatures make the
default Xy tip-style unsuitable for general use.

But using CM tips instead alleviates the problem, as
the positioning of the arrow-tip no longer looks wrong.

>
> ishanu
>

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 +2 9850 8955
Sydney, Australia  2109                            fax: +61 +2 9850 8114
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