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[Christian Jakob <1229783@xxxxxxxxxxxxxxxxxx>]

> If I have a clump with, let's say, 20 particles. Will there be 20
> computations of inertia (each time we add a new member) or only one?

Bruno, as you know there are several ways of creating/modifying a clump.

Each call of Clump::updateProperties(clumpBody); 
will cause approximation of inertia and this takes some time...

updateProperties is called in following methods:

- clump() (see [1])
- appendClumped() (which calls clump() method)
- addToClump() (see [2])
- releaseFromClump() (see [3]) and
- replaceByClumps (which also calls clump() method)

If you use addToClump() method it is possible to add more than one body
via python list. The updateProperties method will be called once per
addToClump() call.

[1] https://github.com/yade/trunk/blob/master/py/wrapper/yadeWrapper.cpp#L152
[2] https://github.com/yade/trunk/blob/master/py/wrapper/yadeWrapper.cpp#L182
[3] https://github.com/yade/trunk/blob/master/py/wrapper/yadeWrapper.cpp#L197

> We should find a default behavior that do not take ages to compute
> anyway, be it at the price of big approximations.

I agree. As you can see here [4] there is a TODO. Edge length of one
cell for approximation of inertia tensor is defined as minimum clump
member radius divided by divisor (actually 15). To avoid worst case of a
clump with one very small member a maximum number of cells is defined
[5]. The maximum number of cells is limited to 150^3 = 3.375 million.

If we change default of divisor (in woo it is 5), the accuracy of inertia approx. will be lower but the scheme would be much faster. I think the best way would be to make it choosable for users (see TODO). 
I can do it with some help from dev-side. Where and can divisor be defined and choosable by users (NOTE that updateProperties is called by 5 methods (see above)!)

[4] https://github.com/yade/trunk/blob/master/core/Clump.cpp#L153
[5] https://github.com/yade/trunk/blob/master/core/Clump.cpp#L156

> loading a clump takes ages indeed (I have clumps with 100 particles) but not
> sure if this is a bug. Maybe there is something wrong with the loops?

Klaus, would you agree with my suggestions? Then you could choose
accuracy/speed of inertia approximation by yourself ;)

-- 
You received this bug notification because you are a member of Yade
developers, which is subscribed to Yade.
https://bugs.launchpad.net/bugs/1229783

Title:
  Loading clumps takes too much time

Status in Yet Another Dynamic Engine:
  In Progress

Bug description:
  The examples/packs/packs.py hangs in line 46 [1] because
  of appendClumped command.

  Changing it to "append" fixes the problem. So, it seems, 
  appendClump has infinite loop  somewhere.

  [1]
  https://github.com/yade/trunk/blob/master/examples/packs/packs.py#L46

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