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@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@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@unimib.it phone: (+39) 02 6448 2321 web: http://www.brunogiacomazzo.org
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