[yt-users] Cell Volume in regions

[Nathan Goldbaum]

Which fields were you comparing with?

On Wednesday, July 9, 2014, Daniel <cunnama at gmail.com> wrote:

> Hi Matt,
>
> No, just loading a standard GadgetDataset:
>
> bbox = [[0.0, 1000000.0],
>         [0.0, 1000000.0],
>         [0.0, 1000000.0]]
>
> unit_base = {'UnitLength_in_cm'         : 3.08568e+21,
>              'UnitMass_in_g'            :   1.989e+43,
>              'UnitVelocity_in_cm_per_s' :      100000}
>
> pf = GadgetDataset("snapshot_050", unit_base = unit_base, bounding_box =
> bbox)
>
> Cheers,
> Daniel
>
>
> On 9 July 2014 17:58, Matthew Turk <matthewturk at gmail.com
> <javascript:_e(%7B%7D,'cvml','matthewturk at gmail.com');>> wrote:
>
>> Hi Daniel,
>>
>> On Wed, Jul 9, 2014 at 10:57 AM, Daniel <cunnama at gmail.com
>> <javascript:_e(%7B%7D,'cvml','cunnama at gmail.com');>> wrote:
>> > Hi Nathan,
>> >
>> > Thanks for getting back to me.
>> >
>> > That is odd, because then if my region includes all the particles I have
>> > equal elements in cell_volume and all the other gas quantities?
>> >
>>
>> Yup, that is a bit odd.  How are you loading the data?  Are you
>> specifying either n_ref or over_refine_factor when doing so?
>>
>> -Matt
>>
>> > Kind Regards,
>> > Daniel
>> >
>> >
>> > On 9 July 2014 15:06, Nathan Goldbaum <nathan12343 at gmail.com
>> <javascript:_e(%7B%7D,'cvml','nathan12343 at gmail.com');>> wrote:
>> >>
>> >> Hi Daniel,
>> >>
>> >> The cell_volume field is an alias for ('gas, 'cell_volume'), which for
>> >> Gadget data corresponds to the volume of octree cells. In general
>> there will
>> >> be fewer octree cells than particles.  I'm a little surprised the
>> numbers
>> >> are so close since the default option is to refine octree cells when
>> more
>> >> than 64 particles are in a cell, although the precise structure of the
>> >> octree will depend on the particle distribution.
>> >>
>> >> Nathan
>> >>
>> >>
>> >> On Wednesday, July 9, 2014, Daniel <cunnama at gmail.com
>> <javascript:_e(%7B%7D,'cvml','cunnama at gmail.com');>> wrote:
>> >>>
>> >>> Hi there,
>> >>>
>> >>> I am extracting a region from a Gadget dataset using the sphere
>> function
>> >>> and then attempting to access the "cell_volume" field.
>> >>>
>> >>> For some reason the number of elements in the cell volume field is not
>> >>> equal to the number of particles in the region.
>> >>>
>> >>> For example I have 4341760 particles but only 4228930 cell volume
>> >>> elements.
>> >>>
>> >>> I have extracted a sphere which encompassed all the particles and the
>> >>> number of cell volume elements is then equal.
>> >>>
>> >>> Any ideas or advice would be greatly appreciated.
>> >>>
>> >>> Kind Regards,
>> >>> Daniel
>> >>
>> >>
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