yade-users team mailing list archive

[Luc Sibille <luc.sibille@xxxxxxxxxxxxxx>]

Hi,

 Is the "normalize" function from wm3 used currently in Yade? I mean 
not in specific packages your are developing at the present time but in 
some basic and usual computation made in Yade.
I think for instance to the computation of the normal vector defining 
the intergranular contact plane (for the DEM), or something else. If yes 
it could a real problem...

Bruno have you got an idea of the default value of the "tolerance" 
value?  The reason for this check could be to avoid a division by zero 
or "something" to close to zero.

Luc



Bruno Chareyre a écrit :
> Hello
>
> Be aware that if you use the "normalize" function from wm3, it might 
> give the result (0,0,0) if the norm of the vector is smaller than a 
> "tolerance" value.
> It sounds very strange to me, as I see no reason for this check, and I 
> was wondering if it could not cause problems in some cases, when a 
> "normalized" vector has length 0...
> Janek had this problem when defining the normal of some triangular 
> facets (of small size) by normalizing the cross product of edges vectors.
> I prefer not to be the only one thinking about this potential problem, 
> which probably needs a fix.
>
> A few ideas from a discussion with Janek :
> 1- possibly fix minWm3 so that the test vs. tolerance is removed
> 2- display a warning to the user when the tolerance is hit and the 
> vector is "rounded" to (0,0,0)
> 3-  run batch tests with/without the tolerance test
>
> Bruno

--
Luc Sibille

Université de Nantes - Laboratoire GeM UMR CNRS

IUT de Saint Nazaire
58, rue Michel-Ange - BP 420
44606 Saint-Nazaire Cedex, France

Tel: +33 (0)2 40 17 81 78