[Users] question about ML_CCZ4 parameters

[Barry Wardell]

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
>
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