[yt-users] yt.lagrangian_volume

Cameron Hummels chummels at gmail.com
Tue Oct 28 13:17:46 PDT 2014


It looks like there is substantial drift in your halos from the start
output to the final output.  As I mentioned previously, the first bounding
box is in the coordinate system of the earliest output.  When it goes above
1, it's just referring to a periodic boundary.  The center of mass is of
the final halo in the later output file, and it doesn't have to be in the
bounding box if there is substantial drift of the halo from the early
output to the final output, as it appears there is in these simulations.
Are you choosing dwarf galaxies, which tend to be more susceptible to drift
in cosmological runs like this?

The final output is the same as the first bounding box, but it has been
shifted over in space, so that the COM of the 2nd step sits at 0.5, 0.5,
0.5.  This makes a lot more sense if you choose a halo which has no drift,
so its center of mass remains inside of the bounding box of the earliest
output.

I'd suggest picking a galaxy which doesn't have so much drift for
re-simulation.  Let me know if you have any other questions!

Cameron


On Tue, Oct 28, 2014 at 12:58 PM, Cameron Hummels <chummels at gmail.com>
wrote:

> Oops.  I just saw that you did include the outputs.  Let me look into this
> and get back to you in a moment.
>
> Cameron
>
> On Tue, Oct 28, 2014 at 12:56 PM, Cameron Hummels <chummels at gmail.com>
> wrote:
>
>> Hi Jingjing,
>>
>> I'm sorry that you're running into some problems with
>> yt.lagrangian_region. Let me see if I can help you.
>>
>> The output of the code should return a box in code units containing all
>> of the DM particles in the selected halo.  I've only tested this with enzo
>> outputs (and I believe that is what you're using it on too), so those code
>> units will go from 0 to 1 in x, y, z.  In addition to this output, the code
>> also will recenter these coordinates so that the final halo coordinates
>> will sit at 0.5, 0.5, 0.5 at the center of the box.  It provides the
>> original box shifted over in coordinates to accomodate this recentering.
>> Lastly, you are correct that some of the coordinates will go above 1 in
>> cases when the particles shift over the periodic boundary condition.
>>
>> Do your results make more sense given this information?  If you're still
>> confused, can you send us the text of your outputs, so that we can try to
>> figure them out?
>>
>> I'm actually working on a newer version of this which will work with yt
>> 3.0 as part of a larger effort to make efficient zoom simulations, but I've
>> not yet finished working on it.  I'll make sure to announce it here when
>> this is complete and ready.
>>
>> Cameron
>>
>>
>> On Tue, Oct 28, 2014 at 12:00 PM, Chen Jingjing <chenjj235 at gmail.com>
>> wrote:
>>
>>> Hi,
>>> I am using the code yt.lagrangian_volume to trace the box that contains
>>> the dark matter particles at an early stage(higher redshift). But I was
>>> quite confused about the output. I am attaching the output file below.
>>> (1) I don't know what the values for the box in the new frame mean, i.e.
>>> what is the unit of these values? It seems to be the normalized scale
>>> because the values are about 1. But it does not seem to be normalized too
>>> because there are some values that are larger than 1. Is that due to the
>>> periodicity of the box?
>>> (2) The bounding box and box in the new frame seems to have the same
>>> size. The difference between the two box is just translation. But I was
>>> expecting that the box should be expanding/collapsing.
>>> (3) The COM (center of mass) in the output is within neither of the box.
>>>
>>> Does anyone know how to explain the box values in the output file?
>>>
>>> Thanks,
>>> Jingjing
>>>
>>> --
>>>
>>> Jingjing Chen [ chenjj235 at gmail.com ]
>>> Department of Astronomy
>>> Columbia University
>>> 550 West 120th Street
>>> New York, New York 10027
>>> Cell Phone: +1(347)5746709
>>>
>>>
>>> _______________________________________________
>>> yt-users mailing list
>>> yt-users at lists.spacepope.org
>>> http://lists.spacepope.org/listinfo.cgi/yt-users-spacepope.org
>>>
>>>
>>
>>
>> --
>> Cameron Hummels
>> Postdoctoral Researcher
>> Steward Observatory
>> University of Arizona
>> http://chummels.org
>>
>
>
>
> --
> Cameron Hummels
> Postdoctoral Researcher
> Steward Observatory
> University of Arizona
> http://chummels.org
>



-- 
Cameron Hummels
Postdoctoral Researcher
Steward Observatory
University of Arizona
http://chummels.org
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