[Users] TOV Solver and Equilibrium

Peter Diener diener at cct.lsu.edu
Thu Oct 22 14:39:55 CDT 2020

Hi Nick,

Your approach of modifiying TOVSolver::TOV_Rho_Central[0] in your 
parameter file just results in an different equilibrium 

However, the TOV-solver actually have built in parameters for doing 
exactly what you want.

If you set

TOVSolve::Perturb[0] = "yes"

you can add a perturbation to the density before writing the initial 
data to the grid.

You'll also need to set TOVSolver::Pert_Amplitude[0] to some nonzero 
value in order for a nonzero perturbation to be added.

The initial data, written to the grid, will of course no longer satisfy 
the constraint equations but for your purpose that should be okay.

Other ways of adding perturbations could also be to use different values 
of TOVSolver::TOV_Gamma and/or TOVSolver::TOV_K for the initial data
thorn and for the evolution thorn.



On Friday 2020-10-16 18:11, Nick Olsen wrote:

>Date: Fri, 16 Oct 2020 18:11:22
>From: Nick Olsen <n.olsen.3.711 at gmail.com>
>To: users at einsteintoolkit.org
>Subject: [Users] TOV Solver and Equilibrium
>I am a master's student working on general relativity and in my project we
>have gotten to a point where we need to solve the Einstein equations. We are
>not numerical relativity experts but we have started getting familiarized
>with the Einstein Toolkit.
>After playing with it for a while I have realized that I can’t even run a
>very simple example where I get the TOV equilibrium parameter file from the
>par folder of the ET installation and modify it to take it a little bit out
>of equilibrium and see it numerically evolve back to a new equilibrium
>situation (say for example changing the density profile). I have tried
>modifying rho_central in the file tov_star.par however it seems that after
>that modification the system does not evolve to a new equilibrium. I was
>wondering if somebody here can point me in the right direction. Thank you so
>much in advance.
>Nicholas Olsen

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