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Johannes Reich
06-21-1999, 11:36 PM
Dear fellownetters,

are you doing threedimensional simulations of rigid body models, which are
described by their geometry, masses, center of masses and inertia tensors?
How sure are you, that your data is at least physical meaningful? This is
probably not a problem with the geometry, masses or center of masses, but
how does an inertia tensor has to look like, to be a physical meaningful
inertia tensor?

We could identify an error in a commercial package, that was supposed to
calculate inertia tensors for a humanoid by these tests:

* It should be positive definit, i.e. all eigenvalues should be strictly
positiv. You can test this by calculating the product for three
independ vectors a and the inertia tensor J. The product should be
strictly positiv for all 3 vectors.

* The sum of two of its diagonal elements must be strictly larger than the
third diagonal element.

I would be interested in your test results.

With kind regards,

Johannes Reich



---------------------------------
| Johannes Reich |
| Hohensandweg 37 |
| Neurologisches Therapiecentrum |
| 40591 Duesseldorf |
| |
| Tel.: (+49) 211 7816 159 |
| Fax.: (+49) 211 576152 |
| email: reich@uni-duesseldorf.de |
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