[Mesa-users] convergence problems in specific mass range

[Warrick Ball]

Hi Thomas,

I've started running your inlist but it's quite slow and it would anyway 
be helpful if you could provide a lot more context.  For example, you've 
said that MESA starts doing retries and backups "at some point", which 
you've also mentioned is around model number 1800.  But what point in the 
star's evolution is this? e.g. has it started burning hydrogen yet?

You've also mentioned that your inlist "works" (without having told us in 
the email what it means to "work", though the inlist has a stopping 
condition of X_c=0.66) for masses M/Msun = 0.54 or 0.56.  What's the 
difference between these three runs? i.e. if you compare the histories of 
the three runs at M/Msun = 0.54, 0.55 and 0.56, what changes?  What about 
profiles for each mass around model number 1800?  And the corresponding 
age (or central hydrogen abundance)?

Another typical thing to do is try switching off your non-default options 
and build back up to the inlist that's not working the way you expect. 
For example, I noticed you're using convective premixing.  Have you tried 
switching that off?  What does that tell you?

These are just some ideas for the kinds of things you can look into that 
will make it easier for someone (yourself included!) to identify a 
solution to your problem.  It sounds like you've already computed enough 
data to ask these more specific questions.

It's also a good idea to clean up your inlists to only contain values that 
have been changed from the defaults.*  It makes it easier for others to 
identify potential issues and rules out some.  For example, you're using 
the non-default reaction network (`pp_cno_extras_o18_ne22.net`).  Does the 
problem persist if you use `basic.net`?  If so, you can just remove all of 
that from the inlist (and it'll allow us to reproduce the problem faster).

Cheers,
Warrick

* Similar advice is given at the beginning of the default 
`star/work/inlist_project` file:

! For the sake of future readers of this file (yourself included),
! ONLY include the controls you are actually using.  DO NOT include
! all of the other controls that simply have their default values.


------------
Warrick Ball
Postdoc, School of Physics and Astronomy
University of Birmingham, Edgbaston, Birmingham B15 2TT
W.H.Ball at bham.ac.uk
+44 (0)121 414 4552


On Tue, 9 Apr 2019, Thomas.Steindl at student.uibk.ac.at wrote:

> Hello everyone,
>
> I am running the same inlist for masses between 0.5 and 6 solar masses with 
> steps of 0.05 solar masses. For some reason, the evolution of the 0.55 solar 
> mass model stops after roughly 1800 steps. All other masses work. If I change 
> the mass to 0.54 solar masses, it works (same for 0.56). Therefore, there is 
> something weird happening in the mass range around 0.55. I have been looking 
> at the temperature, pressure, opacity and density profiles, yet I cannot find 
> unexpected behavior.
>
> To clarify what happens: I am using MESA version r11532. At some point MESA 
> starts doing retrys and backups until the timestep is to small. Taking a 
> smaller limit for min_timestep_limit does not work - it will still stop. I 
> have been checking the output of the newton solver - it takes up to 25 
> iterations at the end until giving up either because of average, max resid or 
> tiny corrections. Additionally, using things like soften_grad_T do not 
> improve the convergence substantially, the evolution just stops a few steps 
> later.
>
> I am attaching the inlist. I would appreciate any help for resolving this 
> problem. Thank you very much in advance.
>
> kind regards,
> Thomas
>