[ODE] A 'real' demo of ODE

[Russ Smith]

> That's interesting to hear, that a single more complex link is faster
> than the sum of its parts. I was under the impression that the
> numerical demand is predominantly dependent upon the number of
> degrees of freedom removed. To use an example: if you
> model the same sort of a link by either a single hinge joint, or by
> using two ball-socket type of links, could you please explain where
> the difference in numerical complexity comes about?

your example (modelling a hinge as two B&S joints) wont work because
they will remove 6 dofs (degrees of freedom) from the system but
a hinge only removes 5. so there will be a singularity.
a better example is modelling a suspension with, say, 3 bodies and
3 hinge joints. sure ... the resulting system has the same number of
degrees of freedom as if you had used a special suspension joint, but 
the 3 hinges are removing 15 dofs from 3 bodies instead of 5 dofs from
just one body. as such the system matrix is bigger, it takes longer to
solve, etc. this is why special purpose constraints are really useful.

russ.

--
Russell Smith
http://www.q12.org