[Users] question about ML_CCZ4 parameters

[Michael Muller]

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

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