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From: Ali Snedden <Ali.P.Snedden.3_at_nd.edu>

Date: Thu, 11 Sep 2014 13:51:48 -0400

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 19:51:58

Date: Thu, 11 Sep 2014 13:51:48 -0400

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 19:51:58

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