[eigen] Allow standard linear algebra operations for quaternions (Bug 560)

[Christoph Hertzberg <chtz@xxxxxxxxxxxxxxxxxxxxxxxx>]

Hi,

it was suggested to inform on this mailing lists about bugs leaving the 
"DECISIONNEEDED" status.

For http://eigen.tuxfamily.org/bz/show_bug.cgi?id=560 we basically 
agreed on the following:

* Have the current Quaternion class represent a generalized quaternion
  and introduce a new class UnitQuaternion which ensures/assumes unity
  everywhere.
* Make all functions assuming unity in Quaternion either deprecated or
  implement them in a conservative way (e.g., implicitly work with the
  normalized quaternion)
  -> That means using the Quaternion class for rotations will lead to
     small overhead avoidable by switching to UnitQuaternion.
* The Quaternion will get additional functionality such as addition and
  scalar multiplication (and maybe higher level functions)

If you have any objections, I'd suggest to bring them up at the 
corresponding bugzilla entry to have all arguments joined in one place.

If you want to take part early in these kinds of decisions, check these 
bugs (more might follow in the future):
http://eigen.tuxfamily.org/bz/buglist.cgi?bug_status=DECISIONNEEDED


Christoph



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Dipl.-Inf., Dipl.-Math. Christoph Hertzberg
Cartesium 0.049
Universität Bremen
Enrique-Schmidt-Straße 5
28359 Bremen

Tel: +49 (421) 218-64252
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