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

[Ana Olímpia]

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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