[mesa-users] other_momentum subroutine

[Ehsan Moravveji]

Dear Sheyda,

If the your quantity “x” has the same dimensionality as pressure, dx/dm seems like a legitimate term to be added to the HSE. In other words, you do not need to multiply/divide by pressure. 
However, make sure that “x” is a cell-averaged quantity (like pressure is), so that the derivative dx/dm is carried out at the face of the cell.

I leave the answer to your other questions to those who have already used s% extra_dpdm.

Best
Ehsan.

> On 18 Jan 2017, at 23:12, sheyda najafi <sh.najafi8590 at gmail.com> wrote:
> 
> Hi MESA users
> 
> I am trying to add an extra term (- dx/dm) to the hydrostatic equilibrium equation as follows:
> 
> dp/dm = - G m/4 pi r^4 - dx/dm
> 
>  or
> 
> (( s%  p(k+1)-    s% p(k))/s% dm_bar(k)) = - (s% standard_cgrav)* s% m(k) / (4*pi* (s% r(k)**4 )) -((   xn(k+1)-    xn(k)) / s% dm_bar(k))
> 
> where x is a new quantity. I am not sure about setting
> 
> s% extra_dpdm(k) = - ((   xn(k+1)-    xn(k)) / s% dm_bar(k))
> 
> Is it correct? or it must be divided by the interpolated pressure to be consistent with the hydrostatic equilibrium equation mesa solve.
> 
> Another question is :  on which side of the hydrostatic equilibrium equation, the term (s% extra_dpdm) is added into the mesa code ?
>  In other words, what is the sign of (dx/dm) in the (s% extra_dpdm) in my case?
> 
> 
> Thank you in advance
> 
> Sheyda Najafi
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