[Mesa-users] split_mixing_choice parameter in MESAv15140

[Anthony Noll]

Hi Evan, hi Rob,

thank you very much for your answers, it's clearer now!

Cheers,
Anthony.

Le 29/09/2021 à 16:56, Evan Bauer a écrit :
> Hi Anthony,
>
> Split mix has been removed from MESA. You're right that this change 
> does not appear to be documented in the the changelog.
>
> There was some discussion back in 2020 among the developers as to 
> whether split mixing was useful for anybody, and the conclusion was 
> reached that nobody felt it was useful enough to maintain. Here's what 
> Bill Paxton had to say at the time:
>
>     split_burn allows us to do multi-substep solves indendently for
>     each zone.  this is important at high temperatures where the
>     simple backward euler can’t give decent results unless we force
>     extremely small timesteps.
>
>     split_mix doesn’t currently have any similar value.   it might be
>     useful if it allowed the newton solver to work on only the
>     structure variables and skip the possibly large number of
>     composition variables.  but that only happens if we do split_burn
>     and split_mix for all cells.  we currently use a logT_start cut so
>     that we only pay the price of the split_burn for high temperature
>     cells that need it.   so we cannot limit the newton to exclude the
>     composition.  so there isn’t really much value to split_mix.
>
>     and for large nets and high temperatures, the total runtime seems
>     to be dominated by the 1 zone burns rather than the matrix solve
>     anyway.  so doing more cells using split_burn in order to make the
>     matrix solve faster is counter productive.
>
>
> Cheers,
> Evan
>
>
>> On Sep 29, 2021, at 10:11 AM, Anthony Noll <anoll at irap.omp.eu 
>> <mailto:anoll at irap.omp.eu>> wrote:
>>
>> Dear MESA users,
>>
>> I noticed that the split_mixing_choice parameter is not available 
>> anymore in MESA r15140. It used to be in MESA r12778, and I cannot 
>> find the reason of this change in the last changelog... Is there any 
>> reason for it?
>>
>> Cheers,
>>
>> Anthony.
>>
>>
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>>
>
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