Numerical Method or Methods used by Bullet

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JDTR75
Posts: 6
Joined: Tue May 22, 2012 12:35 am

Numerical Method or Methods used by Bullet

Post by JDTR75 »

Hi everyone,

Before creating this topic, I was trying to get my answer by searching other posts in the forum but didn't find anything concrete. As the subject says, I would like to know, what are the numerical methods used by Bullet? (searching through the forum I found some other posts that talk about symplectic Euler, Velocity Verlet, Leapfrog integration, etc). I want to know this because I'm doing simulations of different control systems (e.g: simple pendulum, double pendulum, inverted pendulum, etc) and I want to compare the data from Bullet against the differential equations of those systems using MATLAB or Octave for example.

To summarize, I'm gonna make an evaluation on how well Bullet performs the calculations. Of course I'll take in account the computational limitations such as floating point, numerical erros (watch the difference between the data from Bullet and the differential equation resolution), etc.

Regards,
JD
rtrius
Posts: 43
Joined: Sat May 26, 2012 1:09 am

Re: Numerical Method or Methods used by Bullet

Post by rtrius »

The rigid body simulation uses symplectic Euler, also called semi-implicit Euler.
Constraints use the maximal coordinate formulation. That is, each rigid body
starts with 6 degrees of freedom and each constraint removes 1 or more
degrees of freedom. The constraints are solved using Projected Gauss-Seidel.
(Basically the same as Gauss-Seidel, but the result is clamped during each iteration.)
For more details, look up "Sequential Impulses", or the paper
"Iterative Dynamics with Temporal Coherence".
JDTR75
Posts: 6
Joined: Tue May 22, 2012 12:35 am

Re: Numerical Method or Methods used by Bullet

Post by JDTR75 »

Thank you so much rtrius !
rtrius wrote:For more details, look up "Sequential Impulses", or the paper
"Iterative Dynamics with Temporal Coherence".
I wonder is you have the link to that paper you're telling. I'll be more than thankful is you have it. The ones that I've found are dead links.
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Dr.Shepherd
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Re: Numerical Method or Methods used by Bullet

Post by Dr.Shepherd »

I used google cache to get the html version. hope this helps.

http://group.artek-vfx.com/?/file/downl ... U1M2ViYTU=
rtrius
Posts: 43
Joined: Sat May 26, 2012 1:09 am

Re: Numerical Method or Methods used by Bullet

Post by rtrius »

The paper is included in Erin Catto's GDC 2005 presentation, which may be found at:
http://code.google.com/p/box2d/downloads/list

The GDC 2013 physics tutorial slides also seem to have been posted there.
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