[Users] question about ML_CCZ4 parameters

Thu Jun 9 13:49:47 CDT 2022

Barry,
  thanks for the information!

Cheers,
Bruno

Il giorno gio 9 giu 2022 alle ore 00:52 Barry Wardell <
barry.wardell at gmail.com> ha scritto:

> Hi all,
>
> The CCZ4 code was written initially by Dana Alic. Erik (and others)
> subsequently made improvements since then. As far as I know, it should be
> effectively implementing the equations as in gr-qc:1106.2254.
>
> With regards to the k3 parameter, Dana previously had this to say:
> "[GammaShift] should actually be 'real' and its default value set to 0.5,
> as it corresponds to the k3 parameter in the CCZ4 paper (
> http://arxiv.org/pdf/1106.2254.pdf). This is important, because it leads
> to fast instabilities if it is set to 1 and coupled with non-zero values of
> the damping terms."
>
> I hope this helps,
> Barry
>
> On Thu, 2 Jun 2022 at 16:02, Michael Muller <mullerm at uoguelph.ca> wrote:
>
>> Hi Bruno,
>>
>> I have gone through the notebook in the past and from what I could see,
>> the version of paper I (10.1103/PhysRevD.85.064040)
>> is implemented in the code, kappa_3 is encoded in the parameter '
>> ML_CCZ4::GammaShift', and the changes for the
>> scaling of kappa_1 and kappa_2 with the lapse (eq.  27 and 28 in paper
>> II, 2013) are not implemented.
>>
>> I hope this helps.
>> Best,
>> Michael Müller
>> ------------------------------
>> *From:* users-bounces at einsteintoolkit.org <
>> users-bounces at einsteintoolkit.org> on behalf of Bruno Giacomazzo <
>> bruno.giacomazzo at unimib.it>
>> *Sent:* Thursday, June 2, 2022 10:04 AM
>> *To:* Erik Schnetter <schnetter at gmail.com>
>> *Cc:* Einstein Toolkit Users <users at einsteintoolkit.org>; Paolo
>> Garimberti <p.garimberti at campus.unimib.it>
>> *Subject:* Re: [Users] question about ML_CCZ4 parameters
>>
>>
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>>
>> Hi Erik,
>>    thanks a lot for the offer to help. I will try to have a look by
>> myself first at the mathematica notebook.
>>
>> Unless anybody else knows on what paper CCZ4 in McLachlan is based on. :-)
>>
>> Cheers,
>> Bruno
>>
>>
>> Il giorno mer 1 giu 2022 alle ore 22:48 Erik Schnetter <
>> schnetter at gmail.com> ha scritto:
>>
>> Bruno
>>
>> Although I was probably around when the CCZ4 formulation was
>> implemented, I don't recall.
>>
>> I usually resolve to archaeology, comparing the equations in the
>> respective Mathematica scripts to equations found in publications. If
>> no one else speaks up, I can assist with this – we'd set up a Zoom
>> meeting, and I can show how to read (or modify!) the Mathematica
>> script that implements these equations.
>>
>> -erik
>>
>> On Tue, May 31, 2022 at 6:21 AM Bruno Giacomazzo
>> <bruno.giacomazzo at unimib.it> wrote:
>> >
>> > Together with a student of mine we are trying to use the CCZ4
>> formulation implemented in McLachlan.  We saw that most parameters are the
>> same as in BSSN, but there are damping factors that need to be selected.
>> >
>> > In Alic et al 2013 (https://link.aps.org/doi/10.1103/PhysRevD.88.064049)
>> they mention 3 damping factors (k1, k2, and k3), but in the param.ccl of
>> McLachlan/ML_CCZ4 only k1 and k2 are mentioned (assuming they are the same).
>> >
>> > Is it because k3 is hardcoded to the value suggested in Alic et al
>> 2013? Or does McLachlan/ML_CCZ4 use a different set of evolution equations
>> (in which case, is there a reference)?
>> >
>> > We were able to find some example parameter files (for example the ones
>> from the Parma group
>> https://einstein.pr.infn.it/gravity/Research/BNS2015.html) and we found
>> that they used indeed k1 and k2 from Alic et al 2013:
>> > ML_CCZ4::dampk1 = 0.05
>> > ML_CCZ4::dampk2 = 0
>> >
>> > We also saw that they added  ML_CCZ4::ML_Theta to the Dissipation vars
>> and set
>> > ML_CCZ4::apply_dissipation   = "never".
>> > The other parameters look the same as when using BSSN.
>> >
>> > Since I never used ML_CCZ4 I want to be sure that I'm setting the
>> parameters correctly and the damping factors seem to be the most delicate
>> point.
>> >
>> > Thanks,
>> > Bruno
>> >
>> > --
>> >
>> > Prof. Bruno Giacomazzo
>> > Department of Physics
>> > University of Milano-Bicocca
>> > Piazza della Scienza 3
>> > 20126 Milano
>> > Italy
>> >
>> > email: bruno.giacomazzo at unimib.it
>> > phone: (+39) 02 6448 2321
>> > web: http://www.brunogiacomazzo.org
>> >
>> > ----------------------------------------------------------------------
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>>
>>
>> --
>> Erik Schnetter <schnetter at gmail.com>
>> http://www.perimeterinstitute.ca/personal/eschnetter/
>>
>>
>>
>> --
>>
>> Prof. Bruno Giacomazzo
>> Department of Physics
>> University of Milano-Bicocca
>> Piazza della Scienza 3
>> 20126 Milano
>> Italy
>>
>> email: bruno.giacomazzo at unimib.it
>> phone: (+39) 02 6448 2321
>> web: http://www.brunogiacomazzo.org
>>
>> ----------------------------------------------------------------------
>> There are only 10 types of people in the world:
>> Those who understand binary, and those who don't
>> ----------------------------------------------------------------------
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>

-- 

Prof. Bruno Giacomazzo
Department of Physics
University of Milano-Bicocca
Piazza della Scienza 3
20126 Milano
Italy

email: bruno.giacomazzo at unimib.it
phone: (+39) 02 6448 2321
web: http://www.brunogiacomazzo.org

----------------------------------------------------------------------
There are only 10 types of people in the world:
Those who understand binary, and those who don't
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