[Users] Unexpected Hamiltonian constraint violation from refinement when using CCZ4

[Peter Diener]

Hi Kenneth,

With the parameter settings using the "Dissipation" thorn, you were not 
applying dissipation to all evolved variables. When using CCZ4 the 
variable Theta is also evolved. When you switched to the "built in" 
dissipation it is automatically applied to all evolved variables.

So I suspect that using the "Dissipation" thorn will work if you add

ML_CCZ4::ML_Theta

to the list of disspation vars, that should work as well.

Cheers,

   Peter

On Thu, 22 Jul 2021, CHEN, Kenneth wrote:

> Hi, Peter,
> 
> Thanks for your suggestions, which are quite helpful. 
> 
> I was using the independent "Dissipation" thorn
> Dissipation::epsdis = 0.1   Dissipation::order = 5
> Dissipation::vars                       = "
>         ML_CCZ4::ML_log_confac
>         ML_CCZ4::ML_metric
>         ML_CCZ4::ML_trace_curv
>         ML_CCZ4::ML_curv
>         ML_CCZ4::ML_Gamma
>         ML_CCZ4::ML_lapse
>         ML_CCZ4::ML_shift
>         ML_CCZ4::ML_dtlapse
>         ML_CCZ4::ML_dtshift
> "
> for RK4, which turned out to be not enough dissipation for damping out the
> high frequency oscillation of the constrain violation.
> 
> Then I turned on the dissipation of ML_CCZ4::epsdiss = 0.1, It worked, no
> more large violation near refinement boundaries. 
> 
> However, not very sure about how these two "epsdis" work differently.  
> 
> BR
> KZ
> 
> 
> 
> 
> 
> ____________________________________________________________________________
> From: Peter Diener <diener at cct.lsu.edu>
> Sent: Thursday, July 8, 2021 10:47 PM
> To: CHEN, Kenneth <kchen at link.cuhk.edu.hk>
> Cc: users at einsteintoolkit.org <users at einsteintoolkit.org>
> Subject: Re: [Users] Unexpected Hamiltonian constraint violation from
> refinement when using CCZ4  
> Hi Kenneth,
> 
> It is expected that the mesh refinement boundaries will reflect
> Hamiltonian constraint violations. From what you have provided us, it is
> not clear whether the level of constraint violations that you see is a
> cause of concern. You specifically mention CCZ4, but have you tried with
> BSSN? Does the constraint violations look better, the same, or worse with
> BSSN?
> 
> It is also possible that an issue like this might be caused by some other
> problem potentially related to parameter settings, so in order to
> investigate this can you provide your thornlist and parameter file?
> 
> Cheers,
> 
>    Peter
> 
> On Sun, 4 Jul 2021, CHEN, Kenneth wrote:
> 
> > While using CCZ4 to simulate a single star, the Hamiltonian constraint
> > violation initially came from the star surface as expected, but after some
> > time, the violation was dominated by areas near corners of refinement
> levels
> > (by Carpet) as shown in following figures, which were strange. Any
> > suggestions?
> >
> > Thanks and regards,
> > KZ
> >
> >
> >
> >
> > [IMAGE]
> > [IMAGE]
> > [IMAGE]
> > [IMAGE]
> >
> >
> >
> >
> 
>