[yt-users] RAMSES units bug in yt-3.0

Matthew Turk matthewturk at gmail.com
Fri May 9 08:46:07 PDT 2014


Hi Sam,

Okay, I've looked over a bit, and I think the correct change would be:

mass_unit = rho_u * length_unit**3.

That should include the correct length unit, and I think will reduce
"density" back to the "unit_d" that's in the parameter file.  If this
looks okay to you, I will push it, but I really do want to make sure
the particle masses are correct.  Can Nick or Romain provide a bit of
guidance here?

-Matt

On Fri, May 9, 2014 at 11:25 AM, Sam Geen <samgeen at astro.ox.ac.uk> wrote:
> OK, interesting. In theory RAMSES should have identical units for both
> particles and gas. I can hunt down a run with particles to test if you like.
>
> Thanks!
> Sam
>
>
> On 09/05/14 17:22, Matthew Turk wrote:
>>
>> Hi Sam,
>>
>> On reflection, I think this might be related to getting the *particle*
>> masses correct.  I will take a look at it as soon as I can.
>>
>> -Matt
>>
>> On Fri, May 9, 2014 at 11:00 AM, Sam Geen <samgeen at astro.ox.ac.uk> wrote:
>>>
>>> Hmm, that looks like it should be "mass_unit = rho_u * length_unit**3" in
>>> line 492. You're right that it mentions the boxlength issue, though.
>>>
>>>
>>> On 09/05/14 16:50, Matthew Turk wrote:
>>>>
>>>> Hi Sam,
>>>>
>>>> Okay, sounds good.  Looking at how code unit attributes are set up:
>>>>
>>>>
>>>>
>>>> https://bitbucket.org/yt_analysis/yt/src/a14a150c7c81850df81346162bdaff271e77eb50/yt/frontends/ramses/data_structures.py?at=yt-3.0#cl-482
>>>>
>>>> suggests to me that length_unit takes into account boxlen, and
>>>> mass_unit does not.  The comments have some indication why this might
>>>> be.
>>>>
>>>> -Matt
>>>>
>>>> On Fri, May 9, 2014 at 10:46 AM, Sam Geen <samgeen at astro.ox.ac.uk>
>>>> wrote:
>>>>>
>>>>> Yep; both this and dd["density"] give cgs values that are too small by
>>>>> roughly a factor of boxlen**3.
>>>>>
>>>>> One other thing I need to try is to make sure I'm using the very latest
>>>>> version of YT; I've been playing around with the Ramses frontend so
>>>>> it's
>>>>> possible my version is somehow out of sync. Will let you know if this
>>>>> fixes
>>>>> things.
>>>>>
>>>>>
>>>>> On 09/05/14 16:42, Matthew Turk wrote:
>>>>>>
>>>>>> Hi Sam,
>>>>>>
>>>>>> Can you verify the units are in fact incorrect in *cgs*?  Something
>>>>>> like this would work:
>>>>>>
>>>>>> ds = load(...)
>>>>>> dd = ds.all_data()
>>>>>> print dd.quantities.total_quantitiy("cell_mass").in_cgs()
>>>>>>
>>>>>> Your second message makes me wonder if there's just a slipup in how
>>>>>> the units are returned.
>>>>>>
>>>>>> -Matt
>>>>>>
>>>>>> On Fri, May 9, 2014 at 10:37 AM, Sam Geen <samgeen at astro.ox.ac.uk>
>>>>>> wrote:
>>>>>>>
>>>>>>> Sorry for the spam; a second bug I've seen is that the density and
>>>>>>> pressure
>>>>>>> unit labels on figures appears to be broken; it seems to print a
>>>>>>> latex-mangled code names for the units rather than the cgs name of
>>>>>>> the
>>>>>>> units; see attached example. Temperature is fine.
>>>>>>>
>>>>>>>
>>>>>>> On 09/05/14 16:28, Sam Geen wrote:
>>>>>>>>
>>>>>>>> Hi,
>>>>>>>>
>>>>>>>> Just to say that in the latest version of yt-3.0 (i.e. since various
>>>>>>>> fields were renamed or re-implemented), I've found a bug in the
>>>>>>>> implementation of "cell_mass", which is giving results that are too
>>>>>>>> low
>>>>>>>> in
>>>>>>>> my runs; I believe the issue is that it's missing a factor of
>>>>>>>> pf["boxlen"]**3 (which is of course only a problem if boxlen is not
>>>>>>>> 1).
>>>>>>>> The
>>>>>>>> previous "CellMass_Msun" worked fine. If I get time I might take a
>>>>>>>> look
>>>>>>>> and
>>>>>>>> issue a pull request, but otherwise I'm just flagging this in case
>>>>>>>> someone
>>>>>>>> else runs into problems; you can just manually multiply the result
>>>>>>>> by
>>>>>>>> pf["boxlen"]**3 until it's fixed.
>>>>>>>>
>>>>>>>> Cheers,
>>>>>>>>
>>>>>>>> Sam
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