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Re: [Question #676451]: optimize camputational time for vibrated granular media


Question #676451 on Yade changed:

    Status: Answered => Open

Andrea Plati is still having a problem:

On 11/30/18 11:42 AM, Bruno Chareyre wrote:
> Your question #676451 on Yade changed:
> https://answers.launchpad.net/yade/+question/676451
> Bruno Chareyre proposed the following answer:
> It is not directly related to computation time but do you know that
> right after adder() there is a burst of kinetic energy because you
> insert new spheres through the previous ones (randomly overlapping in
> the same volume)?

Yes i know, and what i call transient is the initial time when the 
particles are still not 2600 in my simulation. If you print also the 
number of particle you see that i reach 2600 grains after x iteration. 
So i want to start the comparison between 300 an 2600 after that time. 
Also the burst in the kinetic energy is something that just affects the 
initial time of the simulation.

> I think I realize why this non linearity appears: you increase the number of particles without changing their size hence the coordination number is increasing. 2400 spheres is when the box is maximally filled, leading to a non linear change between 2000 and 2400.
> Maybe ligghts implementation of Hertz is more efficient and then this effect is less visible? I also suspect Ig2_Facet_Sphere, which generates and manipulate matrices every time even for virtual interactions [1].
> This is actually a strange case to test scaling since the number of
> spheres cannot exceed ~2500 by definition...

It is surely a strange case but it is what i need for my research. I'm 
studying what's happen in this setup when i increase the packing 
fraction of the system and so when i increase the number of particles 
(without changing the size) in the same volume. Maybe there is no reason 
to obtain linearity for "CPU time VS N" in these conditions because the 
number and the complexity of the interaction is increasing in a non 
trivial way. Looking at the source code i've found that the 
implementation of Hertz-Mindlin is a little bit different in the two 
softwares and maybe this would be an element to take in account. I will 
also study Ig2_Facet_Sphere.

In any case i'm doing a more systematic analysis and i will share to you 
results and raw data soon

Thanks a lot for this interesting discussion!


> Bruno
> [1]
> https://github.com/yade/trunk/blob/2018.02/pkg/dem/Ig2_Facet_Sphere_ScGeom.cpp#L36

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