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@cfa.harvard.edu http://hea-www.cfa.harvard.edu/~jzuhone ================================

On May 31, 2016, at 9:15 AM, Huebl, Axel 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.

Bautzner Landstrasse 400, 01328 Dresden POB 510119, D-01314 Dresden Vorstand: Prof. Dr.Dr.h.c. R. Sauerbrey Prof. Dr.Dr.h.c. P. Joehnk VR 1693 beim Amtsgericht Dresden

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Hi Axel, Just a quick question, are you all using mol and candela in your code? How do you envision the units representation in your files working with yt’s? Best, John

On May 31, 2016, at 1:05 PM, Huebl, Axel wrote:

Hi John,

independent of the dev branch, I am really just referring to the written proposal in YTEP-0028 as of https://ytep.readthedocs.io/en/latest/YTEPs/YTEP-0028.html https://ytep.readthedocs.io/en/latest/YTEPs/YTEP-0028.html .

I was just wondering since it is still "in progress" and we are implementing the openPMD description right now as a frontend which can express each quantity as a power to the seven SI base units in a generic fashion:

https://git.io/vriio https://git.io/vriio example: https://git.io/vrdpA https://git.io/vrdpA

Sounds great to extent the new UnitSystem a bit further to cover those. Allowing an additional measure for the angles is actually a nice thing - I like that, it's quite a common representation problem.

Best, Axel

On 31.05.2016 15:36, John ZuHone wrote:

...

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. x-apple-data-detectors://0>, MS-67 (w) 617-496-1816 tel:617-496-1816> Cambridge, MA 02138 x-apple-data-detectors://1/1>. (m) 781-708-5004 tel:781-708-5004>

john.zuhone@cfa.harvard.edu mailto:john.zuhone@cfa.harvard.edu mailto:john.zuhone@cfa.harvard.edu> http://hea-www.cfa.harvard.edu/~jzuhone http://hea-www.cfa.harvard.edu/~jzuhone ================================

On May 31, 2016, at 9:15 AM, Huebl, Axel mailto:a.huebl@hzdr.de mailto:a.huebl@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.

Bautzner Landstrasse 400, 01328 Dresden POB 510119, D-01314 Dresden Vorstand: Prof. Dr.Dr.h.c. R. Sauerbrey Prof. Dr.Dr.h.c. P. Joehnk VR 1693 beim Amtsgericht Dresden

_______________________________________________ yt-dev mailing list yt-dev@lists.spacepope.org mailto:yt-dev@lists.spacepope.org mailto:yt-dev@lists.spacepope.org> http://lists.spacepope.org/listinfo.cgi/yt-dev-spacepope.org http://lists.spacepope.org/listinfo.cgi/yt-dev-spacepope.org

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--

Axel Huebl Phone +49 351 260 3582 https://www.hzdr.de/crp https://www.hzdr.de/crp Computational Radiation Physics Laser Particle Acceleration Division Helmholtz-Zentrum Dresden - Rossendorf e.V.

Bautzner Landstrasse 400, 01328 Dresden POB 510119, D-01314 Dresden Vorstand: Prof. Dr.Dr.h.c. R. Sauerbrey Prof. Dr.Dr.h.c. P. Joehnk VR 1693 beim Amtsgericht Dresden

_______________________________________________ yt-dev mailing list yt-dev@lists.spacepope.org mailto:yt-dev@lists.spacepope.org http://lists.spacepope.org/listinfo.cgi/yt-dev-spacepope.org http://lists.spacepope.org/listinfo.cgi/yt-dev-spacepope.org