Real-Time Physics Simulation Forum

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

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".

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.

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

http://group.artek-vfx.com/?/file/downl ... U1M2ViYTU=

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.