# Physics Simulation Forum

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 Post subject: Bender's error correctionPosted: Mon Jun 18, 2012 8:06 pm

Joined: Mon Jun 18, 2012 8:00 pm
Posts: 3
Hi, I am new here. I am trying to understand the bender's error correction in a bilateral constraints problem. Can anybody give me any help on that? Thanks!

Cherry

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 Post subject: Re: Bender's error correctionPosted: Tue Jun 19, 2012 8:30 am

Joined: Fri Sep 08, 2006 1:26 pm
Posts: 106
Location: Germany
Quote:
Hi, I am new here. I am trying to understand the bender's error correction in a bilateral constraints problem. Can anybody give me any help on that? Thanks!

Can you specify your problem with the method?

Jan

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 Post subject: Re: Bender's error correctionPosted: Tue Jun 19, 2012 3:32 pm

Joined: Mon Jun 18, 2012 8:00 pm
Posts: 3
Hi, Jan:
I saw you mentioned the paper: "Fast Dynamic Simulation of Multi-Body Systems Using Impulses" in an earlier discussion:
viewtopic.php?f=4&t=878

Is this the right paper I should follow? Or your earlier paper: "An impulse-based dynamic simulation system for VR applications"? I am now doing a very simple bilateral constraint problem: a pendulum. I already know how to simulate the motion of the pendulum stick in an impulse-based method with constraints. But I still don't know how to do the position correction considering the stability.

Thanks
Cherry

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 Post subject: Re: Bender's error correctionPosted: Thu Jun 21, 2012 7:55 am

Joined: Fri Sep 08, 2006 1:26 pm
Posts: 106
Location: Germany
Hi,

I don't know what you mean with "the position correction considering the stability". Maybe the following paper can help you:

http://i31www.ira.uka.de/~jbender/Papers/STAR.pdf

For computing the impulses p you must solve the following linear system:

J M^-1 J^T p = dv

where J is the Jacobian of the constraints and M is the mass matrix. For the Lagrange multiplier method you have exactly the same matrix. In contrast to other methods you obtain the right hand side of the system dv by making a preview of the joint state. This solves the drifting problem.

Jan

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 Post subject: Re: Bender's error correctionPosted: Fri Jun 22, 2012 3:25 pm

Joined: Mon Jun 18, 2012 8:00 pm
Posts: 3
This paper explained a lot! Danke schoen!

Cherry

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