[Q] ElastoLab Physics

Joshua 'Schwa' Gargus schwa at cc.gatech.edu
Tue Oct 21 13:40:36 UTC 2003


On Tue, Oct 21, 2003 at 06:59:22AM +0200, Karl Ramberg wrote:
> 
> 
> David Buck wrote:
> > 
> > >
> > >
> > >Hello!
> > >
> > >Have anyone figured out how to use the ElastoLab physics package? I would
> > >like to try it with a simulator I am working on but can't figure out how to
> > >set things up. Is there any good examples for this somewhere?
> > >
> > As Karl said check out the testcases in the class
> > SimulatedPhysicsTestcases for examples.
> > 
> > >Do particles collide?
> > >Can you have objects other than round particles? For example a simple
> > >square as a physical object?
> > >
> > >Thanks! Johannes.
> > >
> > <the short answer>
> > 
> > No, no, and no.
> > 
> > <the long answer>
> > 
> > Particles don't collide because the math gets too hard.  Physics is easy
> > to solve when the functions are smooth and continuous and there are no
> > sudden changes.  With springs and elastics, you can step forward at 0.1
> > second intervals and accurately predict where the particle is going to
> > be.  With collisions, you (in theory) have to reduce your step size
> > suddenly to 100 microseconds or smaller to figure out how the collision
> > occurs.  After the collision, you would have to return the step size to
> > something bigger in order to calculate quickly enough.
> 
> A simulation that changed the step time would be interesting, do you
> know of any such implementation ? The simulation would be more 'real' 
> in the sence that real object move, don't jump a longer and longer distance.
> This implementation would have it's own set of problems but solve others.

One of the code phrases for this technique is "adaptive time stepping", which
will turn up many hits on Google.  Unfortunately, I didn't immediately see a
page that provides an overview.  This might be because the concept itself is
not difficult to grasp, but the implementation is dependent on the particular
problem domain (collision detection is only one application).

Joshua


> 
> Karl



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