[mesa-users] density and sound speed profiles with "ripples" in solar calibration example

Thu Aug 28 09:15:09 EDT 2014

Hi Bill,

thank you for your recommendation. Very nice paper that I am reading right
now. I know that there is a more recent version of CESAM, named CESAM2k,
but the one I used to my solar model was a very old version of CESAM (I
think version 4.0.0.0 from 1998?).
Since I am not an expert with any stellar evolution code and I have to
learn it from the beginning I wish I could make some progress with MESA :)

Cheers,
Ana

On Fri, Aug 22, 2014 at 8:52 PM, Bill Paxton <paxton at kitp.ucsb.edu> wrote:

> Hi Ana,
>
> For a nice overview of CESAM, I recommend this paper.
>
>
>
> The numerical techniques it uses are very elegant.  However they may be a
> factor in the limited domain of application, namely pre-ms to onset of
> helium burning.  At least that was the limit as of 1997 when the paper was
> published; perhaps it has changed since then?  But for solar models it
> should be a great tool.  It will be interesting to see how mesa can do in
> comparison!
>
> Cheers,
> Bill
>
>
>
>
>
>
>
> On Aug 22, 2014, at 12:34 PM, Ana Olímpia wrote:
>
> Hi Warrick,
>
> It helped a lot!
> Your explanations were really useful :)
>
> Cheers,
> Ana
>
>
> On Fri, Aug 22, 2014 at 3:37 PM, Warrick Ball <
> wball at astro.physik.uni-goettingen.de> wrote:
>
>> Hi Ana,
>>
>> I thought I'd chip in here because I have a small amount of experience
>> with CESAM, and some knowledge of how it works.  I'm not sure if my variant
>> of the code is the same as yours, but here's what I know anyway. And keep
>> in mind that I'm no CESAM expert, so invite any to overrule me!
>>
>> The numerical method in CESAM is unlike other stellar evolution codes:
>> there is no finite differencing or relaxation.  Instead, the structure of
>> the star is expressed as a sum of basis functions that span some functional
>> space.  In CESAM, it boils down to supposing that the functions are
>> something like piecewise polynomials with compact support i.e. restricted
>> to a small region of the dependent variable.  (These are basis splines, or
>> B-splines, if I remember correctly.)  This method is known as "collocation".
>>
>> In this scheme, the differential equations of stellar structure become
>> equations relating the coefficients of the basis functions in the sums that
>> define the functions, and the "meshpoints" in the stellar model correspond
>> to the locations at which these equations are formulated.  The splines have
>> derivatives that can also be evaluated at those same points. The
>> block-diagonal form of the matrix returns because the coefficients then
>> depend on some number of neighbouring points, depending on the order of the
>> polynomials.
>>
>> But the long and short is that, yes, I think all the structure variables
>> are defined at the same collocation points, rather than distinguishing
>> between cell averages and faces.
>>
>> Hope that helps!
>>
>> Cheers,
>> Warrick
>>
>>
>>
>> On Fri, 22 Aug 2014, Ana Olímpia wrote:
>>
>>  Hi again!
>>>
>>> I was reading the cesam's manual and it looks like it does not use the
>>> concept of cell. I think it works with a
>>> system of concentric spheres with different values of R (radius) and the
>>> other parameters are taken at the surface
>>> of these spheres.
>>>
>>> Regards,
>>> Ana
>>>
>>>
>>>
>>> On Fri, Aug 22, 2014 at 12:54 AM, Ana Olímpia <anaolimpiabrito at gmail.com>
>>> wrote:
>>>       Hi Francis,
>>>
>>> I always thought they were defined all at cell centers but now that you
>>> are asking I realize that I have to
>>> take a look at the manual. I'm not sure about that.
>>>
>>> Regards,
>>> Ana
>>>
>>>
>>> On Thu, Aug 21, 2014 at 4:32 AM, Francis Timmes <fxt44 at mac.com> wrote:
>>>       hi ana,
>>>
>>>       … and along the lines of bill’s earlier message, are the
>>>       cesam numbers defined at cell centers, cell edges, or something
>>> else?
>>>
>>>       fxt
>>>
>>>
>>>
>>>
>>>
>>>       On Aug 20, 2014, at 8:20 PM, Bill Paxton <paxton at kitp.ucsb.edu>
>>> wrote:
>>>
>>>       > Hi Ana,
>>>       >
>>>       > Thanks for sending your solar results.  They are certainly
>>> smooth, but the sound speed match
>>>       to the solar data isn't quite up to the other codes.   I image
>>> this is just a result of not
>>>       doing as many cycles of calibration.  I've attached the data being
>>> used for the comparisons in
>>>       this plot in case you'd like to check that I've correctly
>>> represented your results in the plot.
>>> > <solar_comparison.pdf>
>>> >
>>> > here are the corresponding rms deviations:
>>> >
>>> > MESA rms 0.000632728747717372
>>> > BBP98 rms 0.000930645900227312
>>> > S09 rms 0.00113436296074351
>>> > Ana using CESAM rms 0.0057738746271799
>>> >
>>> > Let me know how things go with the "ripples".
>>> >
>>> > Cheers,
>>> > Bill
>>> >
>>> > <csound.data>
>>> >
>>> >
>>> >
>>> >
>>> > On Aug 20, 2014, at 7:13 PM, Ana Olímpia wrote:
>>> >
>>> >> Hi Bill,
>>> >>
>>> >> thank you for replying so quickly!
>>> >> I will follow your suggestions (I have not done any of them yet) and
>>> then I will let you know the
>>> results.
>>> >>
>>> >> I am sending attached the file with the cesam output for my solar
>>> calibration (radius is the first
>>> column and csound^2 the last one).
>>> >> If you need something else, please let me know.
>>> >>
>>> >> Regards,
>>> >> Ana
>>> >> <sun_cesam.txt>
>>> >
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>>>
>>>
>>>
>>
>> ------------
>> Warrick Ball
>> Postdoc, Institut für Astrophysik Göttingen
>> wball at astro.physik.uni-goettingen.de
>> +49 (0) 551 39 5069
>
>
>
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