[yt-users] Athena units

[John ZuHone]

No worries--it just points to the importance of getting these things documented soon.

On Oct 22, 2013, at 12:39 PM, Nathan Goldbaum <nathan12343 at gmail.com> wrote:

> Ah, sorry for the misinformation!
> 
> 
> On Tue, Oct 22, 2013 at 9:36 AM, John ZuHone <jzuhone at gmail.com> wrote:
> But, "z-velocity" is a defined derived field in the Athena frontend, and should give it in CGS units.
> 
> On Oct 22, 2013, at 12:32 PM, Nathan Goldbaum <nathan12343 at gmail.com> wrote:
> 
>> Yes, velocity_z is in code units as well because it's an athena field.  You'll need to define a new x-velocity field (to match the naming scheme elsewhere in yt) that converts the athena velocity field to CGS.
>> 
>> This is all being fixed with our new sympy powered units system and will be much easier in yt 3.0 or 3.1 (whichever version gets the new units support).
>> 
>> -Nathan
>> 
>> 
>> On Tue, Oct 22, 2013 at 9:23 AM, John ZuHone <jzuhone at gmail.com> wrote:
>> Hi Stephanie,
>> 
>> First off, if I recall correctly we only support setting LengthUnits, DensityUnits, and TimeUnits. Everything else (such as mass, velocity, energy, etc.) should be derived from those. 
>> 
>> Secondly, the reason why you're seeing this for the grid "z" is that it always defaults to the code units (as well as "x" and "y", and the cell deltas). I don't think we have a built-in field for "z" in centimeters (or anything else other than code units), so I think you might have to define a field on your own for "z" in whatever units you want.
>> 
>> Anyone else want to chime in?
>> 
>> Best,
>> 
>> John
>> 
>> On Oct 22, 2013, at 11:31 AM, Stephanie Tonnesen <stonnes at gmail.com> wrote:
>> 
>>> Hi John,
>>> 
>>> Thanks for this.  So I now have this in, and it is being applied to my SlicePlot and ProjectionPlot, but my pc.add_phase_object is still using code units.  There is an excerpt below.  
>>> 
>>> >pf = load("id0/rps."+outstring[i]+".vtk",parameters={"TimeUnits":9.78262,"LengthUnits":26.,"DensityUnits":9.999e-30,"VelocityUnits":2.6e3,"MassUnits":2.596e6})
>>> >pc = PlotCollection(pf)
>>> >tracerp25 = alld.cut_region(["grid['specific_scalar[0]'] > 0.25", "grid['z'] > 0.01"])
>>> >pc.add_phase_object(tracerp25,["z","velocity_z","CellMass"],weight=None,x_log=False,y_log=False)
>>> 
>>> Can I force it to use physical units?
>>> 
>>> Thanks,
>>> Stephanei
>>> 
>>> 
>>> 
>>> 
>>> On Mon, Oct 21, 2013 at 10:24 PM, John ZuHone <jzuhone at gmail.com> wrote:
>>> Stephanie,
>>> 
>>> You can set it up like this:
>>> 
>>> pf = load("virgo_weak_mag.0054.vtk",
>>>                  parameters={"TimeUnits":3.1557e13,
>>>                                          "LengthUnits":3.0856e24,
>>>                                          "DensityUnits":6.770424595218825e-27})
>>> 
>>> Sorry, this is a little-documented feature.
>>> 
>>> Best,
>>> 
>>> John
>>> 
>>> On Oct 21, 2013, at 10:20 PM, Stephanie Tonnesen <stonnes at gmail.com> wrote:
>>> 
>>> > Hi Again, Everyone!
>>> >
>>> > So I would also like my figures to be in physical units, instead of in my code units.  I *think* the Athena frontend doesn't read in what the unit conversions are (and I am not sure how it would do that).  Can I just do something simple like:
>>> >
>>> > DensityUnits = 3.
>>> > density_physunits = grid['density'] * DensityUnits
>>> >
>>> > Then, of course, I don't know how I would do a SlicePlot, ProjectionPlot or phaseplot in physical units...
>>> >
>>> > Any help/advice/direction is appreciated!
>>> >
>>> > Thanks,
>>> > Stephanie
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