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[Chareyre <806944@xxxxxxxxxxxxxxxxxx>]

Damping: no, PFC and YADE's global damping implementations are not
exactly the same, because PFC uses v(t) while Yade uses predicted
v(t+dt/2) to define the sign of the damping force.

I think it is generally pointless to compare results including some
damping (local or global) if the objective is to compare constitutive
laws and dynamic behaviour. It will usually ends like here, wondering
what is the equivalent mass of static+dynamic interaction. A question
unrelated to the initial problem and without clear physical meaning,
since such dampings are numerical tricks. Damped simulations should only
be compared for quasi-static evolutions.

The most interesting result above is IMO:

case3: no damping at all

YADE: flyback_height = 0.133156194762
PFC (notension on): flyback_height = 0.1329
PFC (notension off): flyback_height = 0.1329

There is a 0.2% difference... I would say the two HM implementations are equivalent (at least for the normal force) and that differences in other parts of the code explain the 0.2%.
For better understanding, it would be good to compare step-by-step positions and forces.

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https://bugs.launchpad.net/bugs/806944

Title:
  different behavoir of Hertz model while comparing PFC and YADE

Status in Yet Another Dynamic Engine:
  New

Bug description:
  Hello,

  During verifiing my model I compared output from PFC 4.0 with the
  output from YADE (bzr2877 on Debian Squeeze 64bit). There I found a
  different behavior between these two programs. I dont know if this is
  a bug or not, but I hope someone can explain the different behavior.

  The model itself is very simple. There are two spheres, an upper one and a lower one. The lower one is fixed and the upper one is falling down to the lower one, collides and jumps back. The value of interest is the flyback height of the upper particle.
  In PFC I measure higher values of flyback height, then in YADE (see log-files in the attachment).

  Can someone tell me why there is a difference in the flyback height?
  (input parameters are the same for both programs ... see caller_two-spheres-jumping.dat for PFC and two-spheres.py for YADE)

  Regards,

  Christian Jakob

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