yade-dev team mailing list archive

[Bruno Chareyre <bruno.chareyre@xxxxxxxxxxx>]

Below is an example (from revno 2514). If somebody see an obvious reason 
for getting a NaN, please let me know; if not, I'll send this to Eigen 
(the first line should be enough).

Bruno


NaN angle found in angleAxisr(q), for quaternion 1 -1.56132e-11 
7.47311e-11 -1.7066e-10, after quaternion product
rbp1.ori * (initialOrientation1.conjugate())) * (initialOrientation2 * 
(rbp2.ori.conjugate()) is:
0.745315 -0.0308916 -0.665997 -1.14489e-10 * 0.745315 0.0308916 0.665997 
-0 * 0.746671 -0.166278 -0.644077 0 * 0.746671 0.166278 0.644077 
-1.47527e-18
with sub-products :
1 -1.56132e-11 7.47311e-11 -1.7066e-10 * 1 9.50188e-19 -2.45305e-19 0


On 26/10/10 15:17, Václav Šmilauer wrote:
> > If I'm the author of this comment in the sources (I am, probably),
> > "close to identity" means close to null rotation. In other words the
> > corresponding rotation matrix is very close to identity matrix.
> > So, let M be a rotation matrix defining a rotation of 10^-8 degrees.
> > Theoretically, M*M^(-1)=Id.
> > Now, do the same numerically with quaternions : let q be the quaternion
> > representing the same rotation as matrix M, and compute q*q.conjugate().
> > It seems, sometimes in Eigen, the result will be NaN.
> > As a workaround, I set angle=0 when angle=NaN.
> >      
> Bruno, could you post that issue to eigen's forums
> http://eigen.tuxfamily.org/index.php?title=Main_Page#Get_support? They
> are very responsive as far as my experience goes and will give us proper
> mathematical explanation about the cause.
>
> v
>
>
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--
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Bruno Chareyre
Associate Professor
ENSE³ - Grenoble INP
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