Hi Nick,

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

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.

Cheers,

Peter

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@gmail.com To: users@einsteintoolkit.org Subject: [Users] TOV Solver and Equilibrium

Hello

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