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

[Nathan Goldbaum]

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

On Thu, Jan 5, 2017 at 7:48 AM John ZuHone <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
>
> On Jan 5, 2017, at 8:24 AM, Axel Huebl <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
>
> 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
>
>
> --
>
> 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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