[mesa-users] Messing with the hydro solver

[Matthew Clayton]

Hi there,

First, a quick thank you to Bill for getting hydro_rotation.f90 to use cgrav, it seems to be behaving itself fine now.

Now, I have some questions about the hydro solver; I'm trying to get the solver to sacrifice accuracy in order to get it through difficult evolutionary stages without slowing down too much, so my questions are about ways the solver is failing:

1. I can change the tolerances for residuals and corrections as acceptance criteria, but if the corrections get too big the solver fails with "avg corr too large". When this seems to depend on the product of the parameters scale_correction_norm and corr_param_factor which are set in private_defaults.inc. They are labelled for "experts only". What bad things will happen if I mess with them? And if I want to change the threshold for "avg corr too large", which one of the two should I preferentially mess with?

2. Sometimes the solver fails due to "tiny corrections". The default for how many tiny corrections you're allowed in a row seems to be 5 (tiny_corr_coeff_limit), but in a couple of places in the test suite it's set to 999,999. What's wrong with tiny corrections and why shouldn't I set this to a big number?

3. Occasionally the solver fails with "adjust_correction failed in eval_equations". A little digging suggests that this happens when the microphysics modules are asked to provide values for things like reaction rates under physical conditions that are outside their acceptable input ranges (the errors come from routines like do_neu and do_ne). Is this right? Or can this happen under other circumstances?

Thanks,
Matthew
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