[yt-users] Calculation of enclosed mass for a given radius

[Matthew Turk]

Hi Latif,

On Thu, Jul 19, 2012 at 8:57 AM, Latif <latifne at gmail.com> wrote:
> Hi Matt,
> Many thanks!
>>
>> 1) You have to do the derived field before your pf is loaded; this
>> will hopefully change at some point.  You're also using add_field here
>> as would normally be done for a profile, but you're using it to define
>> a new derived field.
>
>
> Sorry, i did not explain it very well. Yes, you are very right one has to
> add a new derived  field before loading a pf. I used add_field here as i
> wanted to make use of it for computing profiles at the moment.
>>
>> 2) We have "CellMassMsun" and "CellMass" fields already -- which do
>> what you're looking to do.  You should be able to do exactly what you
>> are doing,
>
> As you know "CellMass" is not computing the enclosed mass( it does not sum
> up the mass with in a certian radius) . Prof.add_fields with accumulation
> flag true computes the enclosed mass radial profile. What i want is to store
> the computed enclosed mass in a new profile field or variable  so that i can
> make use of it to compute other profiles like keplerian velocity etc. At the
> moment i do not know how to store enlcosed mass. That is why  i thought to
> add a new prof field for this purpose. Does it make sense? Please let me
> know it is not clear.

Ah, I see.  You can do this:

prof = BinnedProfile1D( ... )
prof.add_fields(["CellMass"], weight = None, accumulation = True)

prof["MassSquared"] = prof["CellMass"]**2.0

Does that give you a hint where you can go?

-Matt

> Cheers
> Latif
>>
>>
>> prof.add_fields(["CellMass"], accumulation=True, weight=None)
>
>
>> which will sum from the low bins to the high bins.  I don't think you
>> need any additional derived fields.
>>
>> Does that help?  We'll add a recipe to do this to the cookbook.
>>
>> -Matt
>>
>> On Thu, Jul 19, 2012 at 7:41 AM, Latif <latifne at gmail.com> wrote:
>> > Hi Guys,
>> > I want to compute the enclosed mass for a given radius to make use of it
>> > for
>> > computing other quantities. I would like  to define a new field like
>> > EnclosedMass. How can i use accumulation flag in combination with new
>> > defined field to compute the enclosed mass(like in prof.add_fields
>> > case).
>> > Unfortunately, add_field does not accept it. May be there be there is
>> > another way to do this.  Any help in this regard will appreciated.
>> >
>> > prof.add_fields("CellMass",weight=None,accumulation=True)
>> >
>> > def EnclosedMass(field,data):
>> >     return data["Density"]*data["CellVolume"]
>> >
>> > add_field("EnclosedMass",
>> > function=EnclosedMass,weight=None,accumulation=True)
>> >
>> > Thanks in advance!
>> > Cheers
>> > Latif
>> >
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