I just uploaded my recent paper about "Impulse-based dynamic simulation in linear time" on my web page:
http://www.impulse-based.de
The paper shows how acyclic models can be simulated in linear time and using linear space with my impulse-based method. I use the same factorization method as David Baraff in his paper "Linear-time dynamics using Lagrange multipliers" but since I use impulses instead of Lagrange multipliers my simulation runs about 6 times faster than Baraff's approach. This is shown in the results of the paper.
So if you are interested just read it
Jan