Physics Simulation Forum

Hi, I'm reading the PHD Thesis "Stable, Robust, and Versatile Multibody Dynamics Animation" of Kenny Erleben in order to implement a rigid body framework.

There is something I don't understand. At the page 99 there is the complete LCP problem formulation (see expression 4.216). Inside this expression, there is some matrices called A_aux and a vector called b_aux.

At the page 100, it's written that A_aux and b_aux correspond to a permutation of the third row and column in 4.61. What does this mean ? I don't understand what are the exact expressions for the A_aux matrix and the b_aux vector.

Could anyone help me to understand what should be put in the matrix A_aux and in the vector b_aux ?
Thanks in advance.

Daniel

Since no-one who knows what they're talking about is helping, I'll try

Looks like Aaux,baux are the friction coupling terms (E = all ones, mu = friction scaling). I don't totally understand what he has done with the friction direction vectors....

I find erleben great for coming up with the constraint jacobians, but hard to use for the full shebam. I combined his stuff with:
http://www.cs.ubc.ca/grads/resources/th ... _Cline.pdf
http://www.gphysics.com/files/IterativeDynamics.pdf

In particular, I believe Erleben is using the nonsymmetric friction formulation which is also a bit harder to solve than that in the iterative dynamics paper....

Thanks for your answer but I still don't understand. Actually, I have a problem to understand the sentence :

"A_aux and b_aux correspond to a permutation of the third row and column in 4.61."

For me, the third row in 4.61 is the matrix:

(-E^t mu 0)

and the third column in 4.61 is the matrix:

(E
0
0)

therefore, for me we have:

A_aux = (-E^t mu 0)

and

b_aux =
(E
0
0)

But I don't really believe that it's true !

Really, no one can help me with my problem ? No one can give me some clue about the meaning of this sentence ? It will help me a lot !

Could you be more specific and explain why you don't believe it's true?

Have you tried asking Kenny Erleben himself at the Open Tissue forums? http://www.opentissue.org/opentissuebb/
Thanks,
Erwin

For instance in the thesis, the vector b_aux seems to be a vector but according to what I have written above, b_aux would be a matrix because E is a matrix of dimension (etha x K) x K.


I'm gonna try !

just curios what's the ending of the story a year later