[yt-users] chemical species abundances discrepancy

[poetaste at gmail.com]

Hi Britton and Matt,
thanks very much for the clarification... the mathematics is clear but  
my question is the following:

If I have a new species which is not defined in YT as _Fraction and I  
would like to plot the mass fraction, how can I avoid such problems  
with the average quantities and binning?
Which is the right procedure starting from the mass density obtained  
from enzo (species_Density)?

Thanks in advance
Stefano

Il giorno 27/gen/14, alle ore 18:34, Britton Smith ha scritto:

> The reason the answers are getting closer together when you add more  
> bins is that you are decreasing the number of points in each bin,  
> and as you do that the difference between
> mean(f * g) and mean(f) * mean(g) will get smaller, though it will  
> not be identical until you have exactly one cell in each bin.
>
>
> On Mon, Jan 27, 2014 at 5:29 PM, Stefano Bovino <poetaste at gmail.com>  
> wrote:
> Ah ok,
> it seems that increasing a lot the number of bins the two approaches  
> are matching better... is there any reason for that?
>
> A second question: how it works for the electrons? In enzo the  
> electrons are usually initialized considering a factor of mp/me, YT  
> takes into account this rescaling?
>
> Thanks again
> Stefano
>
>
> On Mon, Jan 27, 2014 at 6:24 PM, Stefano Bovino <poetaste at gmail.com>  
> wrote:
> ah... I'm binning, it also depends on the number of bins I'm using,  
> but the discrepancy (slight) is still there):
>
> prof3 = BinnedProfile1D(sph3, 64, "Radiuspc", 1.0e-6, 1.0e6)
>
> In my initial setup I'm using a box of 300 pc.
>
> Stefano
>
>
> On Mon, Jan 27, 2014 at 6:20 PM, Stefano Bovino <poetaste at gmail.com>  
> wrote:
> Hi Matt,
> thanks for the quick reply.
> I'm using simple data from the enzo Collapse Test (27).
> It seems is mainly related to the size of the sphere I'm taking...  
> but I don't know.
>
> Here following a piece of my script:
>
>  pf3=load("DD0003/DD0003")
> c3= pf3.h.find_max("Density")[1]
> sph3 = pf3.h.sphere(c3, (100, 'pc'))
> prof3.add_fields("H2I_Density")
> prof3.add_fields("H2I_Fraction")
> prof3.add_fields("Radius")
>
> ...
> ...
>
> d_ax2.loglog(prof3['Radius'], prof3['H2I_Density']/prof3['Density'],
>             lw=1.5, linestyle='--', color='r')
> d_ax2.loglog(prof3['Radius'], prof3['H2I_Fraction'],
>             lw=1.5, linestyle=':', color='y')
>
> Thanks in advance
> Stefano
>
>
> On Mon, Jan 27, 2014 at 6:11 PM, Matthew Turk  
> <matthewturk at gmail.com> wrote:
> On Mon, Jan 27, 2014 at 12:14 PM, poetaste at gmail.com <poetaste at gmail.com 
> > wrote:
> > Hi Guys,
> > I did a simple test with enzo and I tried to plot a radial profile  
> of the
> > chemical species fractions with YT.
> >
> > The problem is that if I use the YT function which intrinsically  
> plot the
> > fraction for a species, let's say H2I_Fraction (as usual), and  
> compare this
> > with a direct evaluation of the mass fraction:
> >
> > data['H2I_Density']/data['Density']
> >
> > I obtain some slightly different results, mostly at large radii.
> >
> > Anyone might explain this discrepancy!? This happens with all the  
> species.
>
> Without knowing what "data" here is, or how you generated it, it's  
> tough to say.
>
> -Matt
>
> >
> > Thank you in advance
> > Stefano_______________________________________________
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