[yt-dev] Microns & Simulation-Specific Unit Base

Thu Jan 5 06:23:47 PST 2017

Yeah, I was thinking that as I was writing it. 

> On Jan 5, 2017, at 8:57 AM, Nathan Goldbaum <nathan12343 at gmail.com> wrote:
> 
> We should have a nicer API for this. Something like astropy's def_unit:
> 
> http://docs.astropy.org/en/stable/api/astropy.units.def_unit.html#astropy.units.def_unit <http://docs.astropy.org/en/stable/api/astropy.units.def_unit.html#astropy.units.def_unit>
> 
> On Thu, Jan 5, 2017 at 7:48 AM John ZuHone <jzuhone at gmail.com <mailto:jzuhone at gmail.com>> wrote:
> Hi Axel,
> 
> You can assign new symbols as well. It sounds like you want to do this for a number of datasets, so you could define new symbols and add them to yt’s unit registry (though you could also add them to a specific dataset’s unit registry). To do the former, you could do something like this in your plugins [1] file (which would ensure they got loaded every time you used yt):
> 
> ```python
> from yt.units.unit_object import default_unit_registry
> from yt.units import dimensions
> 
> default_unit_registry.add("lambda_0", 8.0e-5, dimensions.length, 0.0, r"$\lambda_0$")
> default_unit_registry.add("omega_pe", 1.0e15, dimensions.rate, 0.0, r"$\omega_\text{pe}$") 
> ```
> 
> The arguments in .add are the name of the symbol, the conversion to CGS+Ampere, the dimensions of the unit, the unit offset (only used for temperature and angle units), and the last is the LaTeX representation. 
> 
> Note that I defined omega_pe as a rate, so you’d have to use its inverse when creating your unit system to define the base time units.
> 
> And yes, as I mentioned above the internal base by which all yt units reference is cgs units + Amperes for current (for historical reasons, mostly). 
> 
> Best,
> 
> John
> 
> [1] http://yt-project.org/doc/reference/configuration.html#the-plugin-file <http://yt-project.org/doc/reference/configuration.html#the-plugin-file>
> 
>> On Jan 5, 2017, at 8:24 AM, Axel Huebl <a.huebl at hzdr.de <mailto:a.huebl at hzdr.de>> wrote:
>> 
>> Ha, I oversaw a link in [1] linking to [2].
>> 
>> Ok, so I can just specify my own unit system in user-code with that.
>> But anyhow, I can't assign it new symbols. Also, do all conversion
>> factors need to go through CGS?
>> 
>> Also, microns turns out to be
>>   .in_units("um")
>> :)
>> 
>> 
>> Axel
>> 
>> [2] http://yt-project.org/docs/dev/analyzing/units/unit_systems.html <http://yt-project.org/docs/dev/analyzing/units/unit_systems.html>
>> 
>> On 05.01.2017 13:59, Axel Huebl wrote:
>>> Hi yt-devs!
>>> 
>>> I have a quick user-question (sorry) and a devel question:
>>> 
>>> First, how to convert to a unit like microns (10^-6 meters) or
>>> pico-seconds? I can't find an example here [1]. I tried
>>> 
>>>  .in_units("mum")
>>>  .in_units("mu m)
>>>  .in_units("1.e-6 m")
>>>  .in_units("microns")
>>>  .in_units("micro meter")
>>>  .in_units("micro meters")
>>>  .in_units("micro m")
>>>  .in_units("μm")
>>> 
>>> and only
>>>  .in_units("1.e-6 * m")
>>> 
>>> does not fail but looks ugly.
>>> 
>>> An orthogonal question: in our domain (laser-plasma physics) unit
>>> systems are scaled by something like the applied laser wavelength or the
>>> plasma density (and more to make a full set).
>>> 
>>> Following again [1] I would implement something like .in_base('plasma')
>>> or .in_base('laserplasma') but those are not scaled to "fixed" reference
>>> quantities as the other base systems but are depending on either user input
>>>  [ length = ("$\lambda_0$", "800 nm"),
>>>    time   = ("$\omega_\text{pe}^{-1}$", "1.e-15 s"),
>>>     ...]
>>> or alternatively scalings the data file already provided. (Ok, the
>>> symbol is always fixed per "in_base" but the value to scale with needs
>>> to be provided.)
>>> 
>>> Is that already possible or any ideas how we could implement that?
>>> 
>>> 
>>> Thanks,
>>> Axel
>>> 
>>> [1]
>>> http://yt-project.org/docs/dev/analyzing/units/fields_and_unit_conversion.html#data-selection-and-fields <http://yt-project.org/docs/dev/analyzing/units/fields_and_unit_conversion.html#data-selection-and-fields>
>>> 
>> 
>> -- 
>> 
>> 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
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