Exercises to extend the code: level 1 - GRTLCollaboration/engrenage GitHub Wiki

Welcome, kung fu coder!

You have chosen level 1. The exercises here are as follows:

1. Write a new diagnostic to track the Momentum constraint. This will closely follow the Hamiltonian constraint diagnostic, but you will need to calculate and extract the relevant quantities from the state vector to find the error as a function of position at each timestep in the evolution.

2. Make the oscillaton into an axion star! Amend the Klein Gordon evolution equation for the scalar field to add a self interaction term, as in equation (5) of this paper. Make plots similar to Fig. 1 by varying the self interaction strength $f_a$. If the self interaction is very strong, the star will destabilise and collapse into a black hole (this is quite challenging and so you might need to go for coffee while it runs).