Neutron star simulations using the Nmesh code

The Nmesh code is intended to allow for more efficient simulations of black

holes and neutron stars. The main goal is to use a discontinuous Galerkin

(DG) method in regions where all evolved fields are smooth and to switch to

a compact finite volume (FV) method in regions with non-smooth matter

fields. We call our FV method compact because it does not need the

overlapping domains usually required by traditional FV methods. For our

simulations we employ a large number of touching computational domains or

elements. The calculations in each element are then largely independent, and

the only element-to-element communication needed, is between nearest

neighbors and involves only boundary points. This means the method allows

for very efficient parallelization. We explain our method and how we use a

trouble score to decide when to switch between the DG and FV methods in each

element. Furthermore, we show some test results for single neutron stars,

and also present first results from binary neutron star simulations.