[Dune] Re: Notification from Dune

[Oliver Sander]

No, it is not a problem of the library.  For the library it is
reasonable to expect that its input surface is consistently
oriented so it can compute consistent normals.

Consider the reference quad.

2----3
|    |
|    |
0----1

I want to extract the boundary and hand it over to my library.
Ideally I would extract

(0,1)
(1,3)
(3,2)
(2,0)

so the library knows that when it goes from p to q on (p,q), the
outward normal is pointing to its right.  But instead the
reference element yields

(0,1)  (outward normal to the right)
(1,3)  (   "      "    "   "   "   )
(2,3)  (outward normal to the left)
(0,2)  (   "      "    "   "   "  )

And the external library can't determine the correct normal anymore.

hope this helps,
Oliver

************************************************************************
* Oliver Sander                ** email: sander at mi.fu-berlin.de        *
* Freie Universität Berlin     ** phone: + 49 (30) 838 75217           *
* Institut für Mathematik II   ** URL  : page.mi.fu-berlin.de/~sander  *
* Arnimallee 6                 ** -------------------------------------*
* 14195 Berlin, Germany        ** Member of MATHEON (www.matheon.de)   *
************************************************************************

On Wed, 18 Oct 2006, Christian Engwer wrote:

> Hi Oliver,
>
> On Wed, Oct 18, 2006 at 02:58:17PM +0200, Oliver Sander wrote:
>>> Would be interesting, why and where you needed the specific
>>> orientation you described.
>>
>> I extract (parts of) the boundaries of my grids and hand them
>> over to an external library.  That library expects consistently
>> oriented d-1-dimensional simplicial surfaces in d-dimensional
>> space (d = 2,3).
>
> But this sounds to me, like the problem is, that your external library
> is based on different referenceelements than dune. As what I
> understand, your lib would also fail, if all normals were oriented
> outwards. Right?!
>
> If this is the case, then it is obviously an issue of your program,
> because dune can not have the fitting reference lements for each and
> every lib out there.
>
> CU Christian
>
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