[ODE] How to do iterative

[Sergio Valverde]

>> What both you and the LCP code are trying to do is solve A*x = b where 
>> A is sparse and there are some constraints.  

Precisely, those constraints is what makes solving a LCP more than solving
a linear system.  That is, you can't solve the system without taking into
account _explicitly_ the constraint satisfaction.

>> Where A and b come from is irrelevant, unless you want to exploit 
>> some other structure in A and b.

Most LCP methods only apply to positive-definite systems (including the
pivoting method used by ODE or the direct method proposed by Baraff) 
That is, certain structure is required if you want to solve the 
system by practical means.

Sergi