[mesa-users] Timestep control

[Bill Paxton]

I routinely use the control 'max_years_for_timestep' in my inlists.  You can of course also set it from your run_star_extras.

Alternatively, if you'd like to go deeper, take a look at run1_star in star/job/run_star_support for the following lines:

               result = star_evolve_step(id, first_try, just_did_backup)
               if (result == keep_going) result = star_check_model(id)
               if (result == keep_going) result = extras_check_model(id, id_extra)
               if (result == keep_going) result = star_pick_next_timestep(id)            
 
This happens for each step -- it does "star_evolve_step", then calls check_model in star, followed by your extras check_model.
After those, it calls star_pick_next_timestep which sets s% dt_next, the timestep for the next step.

Then after a few more housekeeping tasks, run1_star calls extras_finish_step. 
So if you change dt_next in your extras_finish_step it will change the next timestep.
You should probably only decrease dt_next -- trying to force larger timesteps is likely to give convergence problems.

Hope that helps.

Cheers,
Bill



On Aug 27, 2014, at 9:30 AM, Dean Townsley wrote:

> Hi Warrick,
> 
> On 08/27/2014 01:37 AM, Warrick Ball wrote:
>> Are there already hooks for the maximum timestep?  Or is it enough 
>> simply to add something like
>> 
>>  s% dt = min(dt, my_dt_limit)
>> 
>> to extras_check_model in run_star_extras?
>> 
> 
> I think you should probably do it in extras_finish_step() instead, and 
> it is s% dt_next.  This is what we have done to control the timestep for 
> accreting WD setups.
> 
> I think s%dt is the either the timestep currently being attempted (when 
> extras_check_model() is called) or the timestep just finished (when 
> extras_finish_step() is called).
> 
> There is also a string somewhere that indicates what is constraining the 
> timestep and is printed in the summary info to the terminal, but I don't 
> know what that is called.  That should probably be changed too, to 
> something like "mylimit" or something more meaningful.
> 
> Dean
> 
> 
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