<div dir="ltr">Michael and Federico,<br><div> thanks a lot for your emails. This information is very helpful.</div><div><br></div><div>Cheers,</div><div>Bruno</div><div><br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">Il giorno gio 2 giu 2022 alle ore 16:30 Federico Guercilena <<a href="mailto:guercilena.federico@gmail.com">guercilena.federico@gmail.com</a>> ha scritto:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr">Dear Bruno,<div><br></div><div>contrary to Erik, I was not around when ML_CCZ4 was implemented, but I used it (or tried to use it) rather extensively.</div><div><br></div><div>Regarding the parameter named k3 in the papers, I'm pretty sure that's the one named GammaShift in the code. It is not hard coded, you can change it in the parfile, but its default value is 0.5 . As noted in the two original CCZ4 papers, this value breaks the covariance of the system (it should be set to 1. for it to be restored), but it allows to handle BH singularities.</div><div><br></div><div>The values of 0.05 and 0 for k1 and k2 (which do correspond to the k1 and k2 of the papers) are "standard" as far as I can tell. Another value I've seen a lot in parfiles for k1 is 0.036, while as far as I know k2 has always been set to 0. I cannot recall any real difference in BNS runs with k1=0.05 or k1=0.036, but I never tried to systematically tune these parameters to "optimal" values.</div><div><br></div><div>Finally, I want to note that I had a lot of subtle problems in using ML_CCZ4 that made me switch to ML_BSSN. These would not be outright crashes, but larger than expected oscillations of stars that in the long term made some simulations unusable to get realistic data, despite the GR constraints violations being much lower than ML_BSSN. When I first encountered this problem, I somehow got the impression that they might be related to some conflict with boundary conditions, but now I'm starting to think that they are related to the values of k1, k2 and k3 not being tuned properly, or maybe even by the system not being strongly hyperbolic (note that as far as I know, there is no actual proof of strong hyperbolicity for the original version of CCZ4 as implemented in McLachaln in the literature. Other versions of the system have been proved hyperbolic, but not this one).</div><div><br></div><div>Actually, if you and your student took the time to do some tuning and managed to improve the performance of this code, that would be pretty interesting in its own right, I think.</div><div><br></div><div>I hope this was of some help.</div><div><br></div><div>Best,</div><div>Federico</div><div><br></div><div><br></div></div>
</blockquote></div><br clear="all"><div><br></div>-- <br><div dir="ltr" class="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div dir="ltr"><p><font color="#000000">Pr<font face="arial, sans-serif">of. Bruno Giacomazzo<br>Department of Physics<br>University of Milano-Bicocca<br></font></font><span style="color:rgb(0,0,0)"><font face="arial, sans-serif">Piazza della Scienza 3<br></font></span><span style="color:rgb(0,0,0)"><font face="arial, sans-serif">20126 Milano<br></font></span><span style="font-size:12.8px;color:rgb(0,0,0)">Italy</span></p><p><font color="#000000"><span style="font-size:12.8px">email: </span><span style="font-size:12.8px"><a href="mailto:bruno.giacomazzo@unimib.it" target="_blank">bruno.giacomazzo@unimib.it</a><br></span><span style="font-size:12.8px">phone: (+39) 02 6448 2321</span></font><br><font color="#000000"><span style="font-size:12.8px">web: </span></font><span style="color:rgb(0,0,0);font-size:12.8px"><a href="http://www.brunogiacomazzo.org/" style="font-size:12.8px" target="_blank">http://www.brunogiacomazzo.org</a></span></p><p><font color="#000000">----------------------------------------------------------------------<br><span style="font-size:12.8px">There are only 10 types of people in the world:<br></span><span style="font-size:12.8px">Those who understand binary, and those who don't<br></span><span style="font-size:12.8px">----------------------------------------------------------------------<br></span></font></p></div></div></div></div></div></div></div>