[ODE] Speed of ODE's constraint method

[alex hamilton]

This iterative LCP solving sounds like the magic bullet for physics in game. 
Is it?

Al






>From: Richard Tonge <rtonge90@yahoo.co.uk>
>To: ode@q12.org
>Subject: [ODE] Speed of ODE's constraint method Date: Sun, 27 Oct 2002 
>10:18:49 +0000 (GMT)
>
>Hello
>
> >perhaps you could tell us exactly what an 'iterative
> >LCP' solver is? i'm genuinely curious
>
>I meant iterative in the sense that the Newton Raphson
>method is an iterative method for finding the roots of
>an equation.
>
>An iterative LCP method is one that makes an initial
>guess of the force vector and then on each iteration
>moves the force vector strictly closer to the exact
>solution. You can then stop the iteration whenever you
>like, if you are willing to accept an approximate
>solution. If you stop the algorithm after one
>iteration, you get an effect that looks quite similar
>to a micro-impulse simulator. If you dont limit the
>number of iterations, you get the exact LCP solution.
>For reasonable size systems with lots of stacks and
>stuff, about 350 iterations looks ok. Each iteration
>does a tiny amount of work (just a constant number of
>4*6 matrix multiplies), so the user has quite fine
>grained control over the execution time (or simulation
>quality).
>
>A good reference on iterative LCP methods is chapter 9
>of Murty's book, which is available online:
>http://ioe.engin.umich.edu/books/murty/linear_complementarity_webbook/kat9.ps
>Although this should give you an idea about what I
>mean by iterative LCP, I should point out that we dont
>use any of the methods in that chapter.
>
> > * re-using constraint clamping info from step to
> >   step?
> >   - if so, how do you handle contact coherency
> >     problems?
> > * in general, how is the LCP restarted?
>
>I think that you are thinking that I was talking about
>a warm starting technique. Whilst it is a good idea to
>do this as well, that was not what I meant by an
>iterative LCP.
>
>Richard Tonge
>PS2 Optimisation Engineer
>MathEngine
>www.richardtonge.com
>
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