arith.diff, arith.ratio

[Laurent Michel]

Hello

I  asked myself the same question when implementing the hardness ratio in MANGO.

The hardness ratio is a unitless quantity (a sort of color) binding 2 fluxes:

       HR = (F2 - F!)/(F1 + F2)

The UCD, phot.flux;arith.ratio, may suggest that the quantity is a flux which is not true.
The quantity is the result of the operation, not the measures used by that operation.
My understanding was that the first term does not necessarily  match the nature of the quantity of the column, this is the role of the entire UCD which must be taken as a whole.

Laurent


> On 1 Sep 2021, at 19:05, Mireille LOUYS <mireille.louys at unistra.fr> wrote:
> 
> Hello Markus,
> 
> we did discuss this point some years ago.
> we reached the agreement that when a mathematical operator is applied to physical quantities,
> what is important is still to keep the emphasis on the physical quantity and not on the operator applied to it.
> 
> Best,
> Andrea Preite Martinez and Mireille Louys
> 
> Le 01/09/2021 à 08:48, Markus Demleitner a écrit :
>> Dear Semantics community,
>> 
>> Since we're puzzling about P and S UCDs a bit already, I'd like to
>> bring up two atoms the status of which I've never quite understood:
>> arith.diff and arith.ratio.
>> 
>> Suppose a table contains a difference between two RA measurements.
>> Going by the UCD spec's:
>> 
>>   While it is possible to build a UCD as a combination of several
>>   simple words, the primary word carries most of the meaning as to
>>   “what the quantity is”.
>> 
>> I would make this "arith.diff;pos.eq.ra", since this is a
>> *difference* (of RAs).  But given that arith.diff is S, I can't do
>> that, and it seems I'll have to go for pos.eq.ra;arith.diff.  That,
>> again, seems very wrong to me, as the column doesn't contain anything
>> like an RA.
>> 
>> A similar reasononing would apply to, say,
>> phys.temperature;arith.ratio.
>> 
>> So... does anyone remember why arith.diff and arith.ratio were
>> labeled S?  Am I perhaps using these atoms against their intended
>> meaning?
>> 
>> Thanks,
>> 
>>               Markus
> 
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