[Mesa-users] Stability Problems with use_other_energy

[Pablo Marchant]

Hi Jose,

my guess is that your implementation needs to be done through the implicit
other_energy option described in
$MESA_DIR/star/other/other_energy_implicit.f90. other_energy is only called
once at the beginning of the step (an explicit calculation), and this can
induce large step-to-step variations. The implicit routines compute the
energy through the Newton iterations and can prevent these large
variations. One detail though is that you need to compute as well partial
derivatives. You can see instructions for this in the source file I
mentioned above.

Cheers

On Thu, Mar 15, 2018 at 9:24 PM, José Lopes via Mesa-users <
mesa-users at lists.mesastar.org> wrote:

> Dear MESA users,
>
> I am developing an extension to MESA to include a Dark Matter Capture
> framework and interplay with the code. This is all done through the
> run_star_extras.f and the ‘use_other_energy’ hook. An extra energy
> contribution is computed for each step (this energy term depends on the
> stellar structure properties, such has the temperature profile and its
> second derivative w.r.t. the radius) and is injected as an extra heat term
> (it can be either positive or negative).
>
> So far most results are consistent with what has already been studied for
> this phenomenology. The problems however start when the extra energy term
> grows to the same order of magnitude of either the nuclear energy or
> gravity energy terms. In these cases, the code shows an irregular
> oscillatory behavior, almost as if it is unable to converge to a stable
> solution.
>
> This oscillatory behavior can be seen in the plots attached to this e-mail
> (plot1 and plot2). There, you can see the nuclear (black), gravity (red)
> and extra (blue) energy terms in the first zone (r ~ 0) of the Star, as a
> function of Model Number. Plot1 shows a case where the extra energy term
> grows to a magnitude comparable to the nuclear energy term, and plot2 shows
> a similar situation for the gravity term. I also attach (plot3) a case
> where the extra energy term is smaller and thus the model is able to
> converge throughout the evolution, although a glitch can be seen in the
> gravity
> energy term.
>
> I have tried tuning some options in the controls inlist (such has time
> step control, variable control, mesh-refinement, etc.). However, so far, I
> have not been able to improve the stability of these models.
>
> As anyone encountered a similar behavior? Is there any control option I
> should focus on to try and improve stability?
>
> Thank you all,
>
> José Vargas Lopes
> PhD Student
>
> CENTRA, Centre for Astrophysics and Gravitation
> IST, University of Lisbon, Portugal
>
> _______________________________________________
> mesa-users at lists.mesastar.org
> https://lists.mesastar.org/mailman/listinfo/mesa-users
>
>
>


-- 
Pablo Marchant Campos
M.Sc on Astrophysics, Universidad Católica de Chile
PhD on Astrophysics, Argelander-Institut für Astronomie, Universität Bonn
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