Re: Pressure and Entropy Units Question

From: Ali Snedden <Ali.P.Snedden.3_at_nd.edu>
Date: Thu, 11 Sep 2014 16:40:31 -0400

Actually, I think my question is answered here.

http://www.mpa-garching.mpg.de/gadget/gadget-list/0136.html

~Ali

On Thu, Sep 11, 2014 at 1:51 PM, Ali Snedden <Ali.P.Snedden.3_at_nd.edu> wrote:

> Hello,
>
> I am trying to work through the units used in SphP[*].Entropy and
> SphP[*].Pressure. I worked through the units of Entropy (see the
> initialization of Entropy in read_ic.c and init.c) and I get units of :
>
> (Internal Energy * (Internal Length)^2 / (Internal Mass^(5/3)) ) in
> Euclidian (i.e. NOT comoving) coordinates.
>
> However when computing the Pressure, in density.c
>
> SphP[i].Pressure = (SphP[i].Entropy + SphP[i].DtEntropy * dt_entr) *
> pow(SphP[i].Density, GAMMA).
>
> This is confusing to me, because it appears that Density is in comoving
> coordinates and Entropy is in Euclidian coordinates. I would expect that
> they should be in the same coordinate system. I would think that there is
> a couple of factors of the scale factor (i.e. All.Time) missing. This
> would convert the Entropy into comoving coordinates so that the Pressure is
> in comoving coordinates.
>
> If Density really is in comoving coordinates and Entropy is in Euclidian
> coordinates, then is the Pressure in comoving or Euclidian coordinates?
>
>
> Sincerely,
> Ali
>
Received on 2014-09-11 22:40:37

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