[yt-users] yt.lagrangian_volume

Chen Jingjing chenjj235 at gmail.com
Tue Oct 28 19:50:56 PDT 2014


Thanks! I think I got it.
But just to make sure that I really understand it: so if I am tracing the
box that contains all the particles which forms a halo at later stage, I
will be using the bounding box whose values are the normalized position of
the bottom left and top right corner of the box. Right?

Jingjing

2014-10-28 16:17 GMT-04:00 Cameron Hummels <chummels at gmail.com>:

> 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
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>>>>
>>>>
>>>
>>>
>>> --
>>> 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
>
> _______________________________________________
> yt-users mailing list
> yt-users at lists.spacepope.org
> http://lists.spacepope.org/listinfo.cgi/yt-users-spacepope.org
>
>


-- 

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
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