[Rock-dev] [Discussion] usage of infinity for "no-data" tagging

[Jakob Schwendner]

On 07/28/2011 02:10 PM, Sylvain Joyeux wrote:
> I've created a proposal for a guideline page for that
>
>     http://rock.opendfki.de/wiki/WikiStart/Standards/RG3
>
> Please discuss. I'll add the relevant bits to base when we agree on the
> proposal.
>
ok for me regarding unset values and the usage of NaN.
I don't agree with the usage of infinity though. Infinity has certain 
properties that do not hold true for an "unknown value".
I've done some tests on inf, because I wasn't 100% sure if my 
assumptions hold, but they do:
a : 1
inf : inf
minf : -inf

a < inf : 1
a > inf : 0
a < minf : 0
a > minf : 1
a / inf : 0
a / minf : -0
a * inf : inf
a * minf : -inf
inf * -5.0 : -inf
inf / -5.0 : -inf

I agree with the usage of inf in covariance matrices (since it's not an 
unknown value there), but not the example with the vector. If you really 
don't want to represent unknown values in a separate variable I would 
even prefer nan in this case.
The thing is you can do normal calculations with inf and even get a real 
number (0) out of it in case you divide another number by inf. Not what 
I would expect from an unknown number.

Jakob

-- 
Jakob Schwendner, M.Sc.
Researcher

DFKI Bremen
Robotics Innovation Center
Robert-Hooke-Straße 5
28359 Bremen, Germany

Phone: +49 (0)421 17845-4120
Fax:   +49 (0)421 17845-4150
E-Mail: jakob.schwendner at dfki.de

Weitere Informationen: http://www.dfki.de/robotik
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