[mesa-users] pseudo-Lagrangian scheme in MESA

Jean-Claude Passy jcpassy at gmail.com
Mon Apr 18 09:43:20 EDT 2016


Hi Bill,

thanks a lot for pointing this out. 
I think Section 7 is very clearly written, and together with Townsley et Bildsten (2004), it answered my questions.    

Cheers,

JC

> On 18 Apr 2016, at 01:41, Bill Paxton <paxton at kitp.ucsb.edu> wrote:
> 
> Hi JC,
> 
> Dean Townsley and I struggled with the terminology in section 7 of the recent mesa instrument paper where is topic is covered in some detail.  Could you please refer to that with a set of more specific questions.  Dean and I will try to answer, although we aren't likely to completely agree about how to say what we both know is going on in the code!   
> 
> Cheers,
> Bill
> 
> 
> 
> 
> On Apr 17, 2016, at 4:35 PM, Jean-Claude Passy wrote:
> 
>> Dear all,
>> 
>> I have some conceptual questions regarding the numerical scheme used in MESA for mass loss/accretion.
>> MESA (among other codes) is said to use a pseudo-lagrangian approach in the outer region of the star to solve the stellar equations. My questions are the following:
>> 
>> 	1) Does it mean that a) the equations are written and solved as a function of q (so there is an extra term in the partial time derivative); or b) the equations are still written in the Lagrangian form and some rescaling is applied (Section 6.6 in Paxton et al. 2011)?
>> 
>> 	2) Why doing that? It must be for numerical reasons, and I’d love to get the details.
>> 
>> 	3) Where are the relevant pieces of code doing that?
>> 
>> 
>> Hope that someone can clarify things for me.
>> 
>> Cheers,
>> 
>> JC
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