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[Kneib François <1301443@xxxxxxxxxxxxxxxxxx>]

Not really, even after the sphere disappears, angVel remains OK, but
always very small. It also not oscillates at timestep timescale. Below
some values of angVel at each time step, before and after body 5
disappears.

O.bodies[5].state.angVel[2] :

9.265986930721519e-161
9.198671437378891e-161
7.230838020503688e-161
3.762575491416308e-161
-5.009685389573714e-162
-3.930775072620818e-161
-6.6976705675296116e-161
-8.314102662474639e-161
-8.495241198140243e-161
-6.9233738378205625e-161

#### Body n°5 disappears ####

-3.877830795599762e-161
2.2185263734549886e-163
3.263461437999207e-161
5.983948968740244e-161
7.704273003639118e-161
8.12129667077455e-161
6.948256554330593e-161

This problem seems to occur in a lot of (not specific) cases, and is
much more visible in 2d simulations as a missing spheres let a hole. I'm
very surprised that nobody have seen this before ...

Thanks for your replies.

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https://bugs.launchpad.net/bugs/1301443

Title:
  Spheres/Box contact : spheres ori suddenly set to NaN.

Status in Yet Another Dynamic Engine:
  New

Bug description:
  Hi,

  Please see and launch the attached script.
  Some spheres are falling into a box because of gravity. The simulation starts well, but when all particles are almost steady, wait for a few seconds and you will see that some of them who are in contact with the bottom wall will disapear. I spent some time to investigate and that's my preliminary conclusions :
  - it is fully reproducible
  - particles don't really disappear : their orientation is suddenly turned to Quaternion(Nan,Nan,Nan,2*pi). It's not linked with a high torque on them. All other attributes remains okay, and the other particles still can interact with it. If you manually set the orientation to a correct value after it disappears, it will appear again at the right place.
  - you can reproduce this with one sphere (uncomment the last line of the script and comment the previous paragraph) : let it fall then apply to it a little angVel : "O.bodies[-1].state.angVel=(0.,0.,0.001)". It will disappear after a few timesteps.
  - it's independent on the timestep value.
  - it's dependant on the interpenetration of the contact : if you increase the gravity or decrease the young modulus, you will be able to avoid this behaviour.

  Does somebody have an idea ? I think it's a rotation calculation
  issue, in a very specific geometric case.

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