# Re: comoving implementation

From: Yves Revaz <yves.revaz_at_obspm.fr>
Date: Tue, 06 Feb 2007 11:15:38 +0100

Thanks,
I did a mistake conserning the soundspeed units.
Now, everything is in order.
Thanks for your help.

>Again, I think the confusion probably arises from not being clear about
>how the variables used by the code translate to physical quantities. For
>example, the "soundspeed" variable (let me denote it with c_c) in
>hydra.c is related to the real physical soundspeed c_p by
>
> c_c = a^(3(gamma-1)/2) c_p
>
>That's because the pressure variable used by the code, P_c, is defined
>as
> P_c = A * rho_c^gamma,
>
>where A is the (physical) entropy (denoted by Entropy in the code), and
>rho_c= rho_p * a^3 is the comoving density. This means that P_c is
>related to the physical pressure as
>
> P_c = a^(3*gamma) P_p
>
>To work out the correct prefactors of a in various places of hydra.c, I
>recommend to first identify the translation between variables used by
>the code (which you may call "comoving" if you like) and the underlying
>physical quantities, and then to start putting this into the basic
>equations in physical units.
>
>
>

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Received on 2007-02-06 11:15:38

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