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enkimute

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enkimute
·작년·discuss
fixed it. mea culpa.
enkimute
·2년 전·discuss
Thank you, appreciate that!
enkimute
·2년 전·discuss
Apologies. Had that joke sitting around for waaaay to long. Not that great in retrospect :D
enkimute
·2년 전·discuss
don't foget the fantastic Sudgy 'A swift introduction to projective geometric algebra' : https://www.youtube.com/watch?v=0i3ocLhbxJ4

and ofcourse the go-to reference https://bivector.net

or join 1000+ profs, researchers and enthusiasts on the bivector discord here https://discord.gg/vGY6pPk
enkimute
·2년 전·discuss
For specifying animations, you should work in the quaternion lie algebra, not in the group as you suggest. There you can represent 1620 degrees without any problem. Furthermore, in the quaternion Lie algebra (pure imaginary quaternions), and only in that space, you can take an arbitrary rotation key, multiply all 3 of its values with 10 and get 10 times that rotation without change in axis.

If you rotate around just one axis, the Lie algebra feels just like Euler angles .. in fact its exactly the same thing, but if you rotate around more than one .. it keeps working intuitively and usably - Euler angles absolutely do not.
enkimute
·2년 전·discuss
done. mea maxima culpa.
enkimute
·4년 전·discuss
There's no smoke. But there surely are mirrors. (Group theory joke)
enkimute
·4년 전·discuss
These are also called the planar quaternions and are the even subalgebra of 2D PGA. I use and explain these (and their nD generalisations) in my SIBGRAPI 2021 talk on kinematics and dynamics in PGA.

https://youtu.be/pq9YfdPHhIo

There is also a writeup called 'may the forque be with you' available on bivector.net
enkimute
·5년 전·discuss
Not the same concrete example, but one where I do find the Geometric Algebra version substantially more insightful, is the treatment of rigid body mechanics in the geometric algebra of the Euclidean group (R_{n,0,1}).

It has the dual quaternions as even subalgebra (in 3D), and unifies all linear and angular aspects. It leads to remarkable new insights, as removing the need for force-couples (pure angular acceleration is caused by pushing along a line at infinity), while pure linear acceleration is caused by forces along lines through the center of mass.

These geometric ideas are independent of dimension - forces, both angular and linear are always lines. The treatment of inertia becomes a duality map, and things like Steiners theorem are not needed at all.

On top of this, the separation of the metric that sets GA apart means that this formulation of rigid body dynamics works not only in flat Euclidean space, but unmodified in the Spherical and Hyperbolic geometries. (by a simple change of metric of the projective dimension).

For a (graphics/game programmer oriented) tutorial on this see https://www.youtube.com/watch?v=pq9YfdPHhIo&ab_channel=Bivec...
enkimute
·5년 전·discuss
Every Lie algebra is a bivector algebra (see 'Lie groups as Spin groups' http://geocalc.clas.asu.edu/pdf/LGasSG.pdf).

Additionally the GA formalism enables closed form solutions for the exponential map for all bivector algebras. (see 'Graded symmetry Groups' https://www.researchgate.net/publication/353116859_Graded_Sy...).