[Users] Large junk radiation

[Roland Haas]

Hello Deborah, all,

Having used both TwoPunctures codes in the past: have you eg dumped the
TP coefficients of both codes to disk after a solve to compare those?
The two may have quite different ways of specifying the mass (e.g. one
can hunt for a given mass on its own, the other uses Baum). 

The quantities to output for comparison would be the v.d0 array in
src/TwoPunctures.c .

Yours,
Roland

> Hi Deborah,
> 
> I'd be curious to see a comparison between the junk radiation you're seeing
> now versus before, for the same physical scenario, grids, etc. Also, the
> extra wiggles/reflections are typically caused not by junk radiation but by
> a sharp gauge feature (https://urldefense.com/v3/__https://arxiv.org/abs/1404.6523__;!!DZ3fjg!8pjNitnVpXn7nbD_Tme73cqSxTqjQfOnBdRnCOoyJTvMp2TaJ5yo1xC_AGTLCz8Gquvy97cfTlFcZ6y2$ ). The two can be
> easily distinguished as the former propagates at c, and the latter at
> sqrt(2) c (see paper for details).
> 
> -Zach
> 
> *     *     *
> Zachariah Etienne
> Assoc. Prof. of Physics, U. of Idaho
> Adjunct Assoc. Prof. of Physics & Astronomy, West Virginia U.
> https://urldefense.com/v3/__https://etienneresearch.com__;!!DZ3fjg!8pjNitnVpXn7nbD_Tme73cqSxTqjQfOnBdRnCOoyJTvMp2TaJ5yo1xC_AGTLCz8Gquvy97cfTjyWM0m7$ 
> https://urldefense.com/v3/__https://blackholesathome.net__;!!DZ3fjg!8pjNitnVpXn7nbD_Tme73cqSxTqjQfOnBdRnCOoyJTvMp2TaJ5yo1xC_AGTLCz8Gquvy97cfTpa-uABN$ 
> 
> 
> On Tue, Aug 9, 2022 at 4:41 PM Erik Schnetter <schnetter at gmail.com> wrote:
> 
> > Deborah
> >
> > One one hand, TwoPunctures has parameters to choose the resolution of
> > the spectral grid it uses. I assume you are aware of these, and that
> > you also know how to choose the 3D AMR grid setup parameters.
> >
> > TwoPunctures only solves for the conformal factor. It does per se not
> > directly choose a lapse and a shift, but their choice is important in
> > practice. Choosing \alpha=1 and \beta^i=0 as initial conditions is
> > often not good. Similarly, choosing the antisymmetry lapse (with
> > \alpha=-1 at the puncture) is also a bad idea (it is ill-posed). The
> > TwoPunctures toolkit in the Einstein Toolkit has several options for
> > choosing the initial gauge conditions. Personally, I am partial to
> > initial_lapse = "twopunctures-averaged", but I am sure that others
> > have other preferences.
> >
> > Of course, the BSSN gauge parameters used during evolution will also
> > play a role.
> >
> > You can look at the gallery example at
> > <https://urldefense.com/v3/__http://einsteintoolkit.org/gallery/bbh/index.html__;!!DZ3fjg!8pjNitnVpXn7nbD_Tme73cqSxTqjQfOnBdRnCOoyJTvMp2TaJ5yo1xC_AGTLCz8Gquvy97cfTr64Mzze$ > for ideas.
> >
> > -erik
> >
> >
> >
> > On Tue, Aug 9, 2022 at 4:47 PM Ferguson, Deborah
> > <deborah.ferguson at austin.utexas.edu> wrote:  
> > >
> > > Hi,
> > >
> > >
> > >
> > > We had been using our own version of TwoPunctures, and I’ve recently  
> > switched to the ETK version since it doesn’t require solving for the masses
> > separately. Junk radiation has always been present, but I’m finding that
> > some of my recent simulations have particularly loud junk radiation, which
> > also makes it harder avoid reflection of. So I’m guessing I’m not fully
> > understanding the TwoPunctures parameters.  
> > >
> > >
> > >
> > > I’ve attached a parfile and a psi4 plot for a simulation I’ve started  
> > that’s having this large junk radiation, and was hoping someone could point
> > out any mistakes I may have in the TwoPunctures parameters.  
> > >
> > >
> > >
> > > Thanks!
> > >
> > > Deborah
> > >
> > >
> > >
> > > --------------------------------------
> > >
> > > Deborah Ferguson
> > >
> > > Post Doc
> > >
> > > University of Texas at Austin
> > >
> > > _______________________________________________
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> >
> >
> >
> > --
> > Erik Schnetter <schnetter at gmail.com>
> > https://urldefense.com/v3/__http://www.perimeterinstitute.ca/personal/eschnetter/__;!!DZ3fjg!8pjNitnVpXn7nbD_Tme73cqSxTqjQfOnBdRnCOoyJTvMp2TaJ5yo1xC_AGTLCz8Gquvy97cfTgTz5FK_$ 
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> >  


Yours,
Roland

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