[yt-dev] Comment on YTEP-0028: No. of Base Units

John ZuHone jzuhone at gmail.com
Tue May 31 06:36:48 PDT 2016


Hi Axel,

First, I presume you are referring to the new unit system functionality in the development branch of yt, correct?

Currently in yt, "mol" is treated as "dimensionless" and we do not have units of candela. I recognize this is different from the SI standard, which has them as base units as you mentioned, and actually treats angles as dimensionless.

There are a couple of things going on here:

1. Angles are given a dimension since they have an important role in the areas of science for which yt was originally tailored to, and it helps things from a design perspective to distinguish them from dimensionless units.

2. The reason for the variance with the SI standard regarding mol and candela is somewhat historical as well; yt originally worked only in CGS units and even now assumes those as a default units base. The support for different unit systems is new. The fact that we treat mol as dimensionless and do not have candela is simply because a use case requiring otherwise has not presented itself yet.

Do you have an application of yt that requires a closer adherence to the SI standard? If so, we'd be willing to look into making some changes along these lines.

Best,

John


================================
John ZuHone, Chandra/ACIS Operations	
Harvard-Smithsonian Center for Astrophysics

60 Garden St., MS-67       (w) 617-496-1816
Cambridge, MA 02138.     (m) 781-708-5004

john.zuhone at cfa.harvard.edu
http://hea-www.cfa.harvard.edu/~jzuhone
================================

> On May 31, 2016, at 9:15 AM, Huebl, Axel <a.huebl at hzdr.de> wrote:
> 
> Dear yt-Developers,
> 
> we found today that the UnitSytem in YTEP-0028 has only 4 (MKS: 5) base
> units + the angular measure.
> 
> This is a bit confusing since the SI unit system has seven base units,
> further including mol (amount of substance) and candela (luminous
> intensity), which are not available.
> 
> Is this intentional?
> 
> 
> Best,
> Axel
> 
> -- 
> 
> Axel Huebl
> Phone +49 351 260 3582
> https://www.hzdr.de/crp
> Computational Radiation Physics
> Laser Particle Acceleration Division
> Helmholtz-Zentrum Dresden - Rossendorf e.V.
> 
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>          Prof. Dr.Dr.h.c. P. Joehnk
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> 
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