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

[Alexander Duda]

On Fri, 2011-07-29 at 09:58 +0200, Jakob Schwendner wrote:
> 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
> 

For me inf is a sentinel value and cannot be measured by any physical
sensor. Therefore in this case inf is just a concept to flag something
like a unknown value.

Alex

-- 
Dipl.-Ing. Alexander Duda 
Unterwasserrobotik

DFKI Bremen
Robotics Innovation Center
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E-Mail: alexander.duda at dfki.de

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