[ODE] How do I code my own constraints ?

[Jason Gott]

Hello,

The best paper I've found for describing the A matrix
and B (right hand side) vector is "Linear-Time
Dynamics Using Lagrange Multipliers" by David Baraff. 
It was in Siggraph '96.  Search for it by name and
you'll find .pdf's.  "Fast Contact Force Computation
for Nonpenetrating Rigid Bodies", also by Baraff
(Siggraph '94) is also helpful.  It talks about LCP's
and Dantzig's algorithm.

As far as figuring out what to put in J (the
constraint matrices), look at ODE's source code for
the different joint types.

Hope that helps!
J

--- Gazza <gazza@shaw.ca> wrote:
> Hi,
> 
> I'm trying to understand how to compute the
> constraints matrix for a particular constraint.
> 
> I'm of the understanding that a 'contact' constraint
> would remove a DOF along the contact normal, thus
> requiring 1 value.  When solved, the force/impulse
> is applied along the normal.  For a ball joint, 3
> DOF's are removed - x,y,z translations,  and for a
> hinge, 5 DOF's are removed - x,y,z translation and
> say x,y rotation.  Am I correct in these assumptions
> ?
> 
> What I don't understand (or can find any
> documentation/papers on) is how the value(s) are
> computed for the A(n*n) matrix and b(n*1) for each
> constraint, which tell the system to remove these
> DOF's.
> 
> Any help given is most appreciated.
> 
> Thanks in advance.
>   Gazza
> 


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