[mesa-users] another mesa question

[Robert Farmer]

Hi Sebastien,

These controls (in your controls section) might also help you adjust the
timestep near the max_age.

         !### num_adjusted_dt_steps_before_max_age

         ! This adjusts `max_years_for_timestep` so that hit `max_age`
exactly,
         ! without needing possibly large change in timestep at end of run.
         ! only used if > 0

         ! number of time steps to adjust to prior to hitting max age
         ! only used if > 0

      num_adjusted_dt_steps_before_max_age = 0

         !### dt_years_for_steps_before_max_age

         ! timestep in years

      dt_years_for_steps_before_max_age = 1d6


Rob


On Mon, Aug 17, 2015 at 9:21 AM, Bill Paxton <paxton at kitp.ucsb.edu> wrote:

> Hi Ehsan,
>
> Thanks for the reminder about the when_to_stop tolerances.  Turns out
> those are relevant for stopping conditions OTHER than age -- such as
> luminosity, mass, radius, etc.  The age is different because the star is
> evolved for specific timesteps so it knows exactly the end time for the
> step.  This is in contrast to things like luminosity where we don't know at
> the start of the step what the value will be at the end.  So for those sort
> of cases, we need to have tolerances to decide when the final value is
> close enough to the target; for age we don't need the tolerances since we
> can predict the end-of-step value precisely.
>
> So something else is going on with Sebastien's example.
>
> Cheers,
> Bill
>
>
>
> On Aug 17, 2015, at 9:07 AM, Ehsan Moravveji wrote:
>
> > Hi Sebastien,
> > I “guess” you’re terminating your run based on an upper age. Given the
> fact that the age difference between your restart model, and your desired
> final model is around 1.32 Myr, then your should already set a small enough
> timestep in your inslist to make sure there are enough steps in between the
> two starting and ending points. Here, “max_timestep” can help you.
> > The second is to have a “precise” control over your landing point. I
> mean, you would like your final model be at 1.81260 Gyr, but how much
> tolerance do you give it?
> > Then, the following two controls are brilliantly designed to tune this:
> >      when_to_stop_rtol = 1d99
> >      when_to_stop_atol = 1d99
> > set them at least to 1d-4 (or even less) and explore if you land on the
> spot you desire.
> >
> > I hope this helped.
> > Ehsan.
> >
> >
> >
> >> On 17 Aug 2015, at 17:57, Bill Paxton <paxton at kitp.ucsb.edu> wrote:
> >>
> >> On Aug 17, 2015, at 5:48 AM, Sébastien Deheuvels wrote:
> >>
> >>> I would like to restart a MESA run for a short period of time. My
> model's age is 1.81128 Gyr, and I would like to evolve it to 1.81260 Gyr.
> But when I run this, I obtain a model with an age of 1.81294 Gyr. There
> seems to be a lower bound to the first timestep for a restart and I could
> not find ways of going around this in the controls options. Do you know how
> I could solve this? Thanks a lot in advance!
> >>
> >> Hi Sebastien,
> >>
> >> That's an interesting question.  Let's get mesa-users involved by
> forwarding it to them to give some other folks a chance to think about it
> -- perhaps someone has encountered this issue previously.  Meantime you
> might send a followup email to mesa-users with the saved mode, the inlist,
> and details of what you tried that failed to work.
> >>
> >> Cheers,
> >> Bill
> >>
> >>
> >>
> >>
> >>
> >>
> >>
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