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[jduriez <duriez@xxxxxxxxxxxxxxx>]

"T the theoretical stability value "

I was wondering if such values exists (I mean, can be theoretically
derived) for any cases (more than two particles along one axis
especially) ?  The (your ?) paragraph you quoted Bruno made me consider
the question...


I just realized that the idea is to consider the discrete numerical model with a vector X =  ( x(body1),y(body1),z(body1),x(body2),y(body2),z(body2),.... ), and write that our DEM computations leads to write 
             X(t+dt) = X(t) * f(dt)         (1)
     With f(t) determined by the fact that the second derivative of X, d²X/dt² is given by a linear system M d²X/dt² + K X = 0, with M and K the "generalized mass and stiffness matrices".
    Then you end up saying that equation (1) is stable for dt values given by the classical relation.


Did I understand well ? If yes, I have still few questions : 
* does this not depend on the integration scheme which is used ? Depending on how we compute X(t+dt) from X(t) and d²X/dt², we do not end up with same f(dt) in equation (1), isn't it ? Then, different values of critical values of dt ? Or not ?

* the consideration of a linear system M d²X/dt² + KX = 0 assumes no
boundary conditions and no gravity, isn't it ?

* in any case, there should be a typo at last line of https://www.yade-dem.org/doc/formulation.html#general-mass-spring-system : m / k does not have the same unit as eigenvalue of M-1 * K 
(it would be difficult for me to perform myself the correction)

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https://bugs.launchpad.net/bugs/897237

Title:
  bug in neverErase?!

Status in Yet Another Dynamic Engine:
  New

Bug description:
  If I set neverErase=True Yade crashes with following output:

  O.run(3000,True)                                                                                                                                                                                             
  RuntimeError: std::exception 

  and also:

  Traceback (most recent call last):                                                                                                                                                                               
    File "/home/me/YADE/YADE2970/lib/yade-bzr2970/py/yade/qt/__init__.py", line 192, in refreshEvent                                                                                                       15:01:13
      self.refreshValues()                                                                                                                                                                                 15:01:30
    File "/home/me/YADE/YADE2970/lib/yade-bzr2970/py/yade/qt/__init__.py", line 265, in refreshValues                                                                                                      15:01:34
      s=int(t); ms=int(t*1000)%1000; us=int(t*1000000)%1000; ns=int(t*1000000000)%1000                                                                                                                             
  ValueError: cannot convert float NaN to integer  

  
  You can reproduce the bug with the attached script (similar to the one i submitted with version 2960).
  First try to set Law2_ScGeom_MindlinPhys_Mindlin(neverErase=False), this will work.
  Then set neverErase=True and yade crashes.

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