Tutorials

In addition to the tests, we will here consider the general settings of the ASWNS code. These settings can be found in the file ASWNS.f90 and determine fundamental constants, but also the grid setup, or iteration details.

If you open ASWNS.f90, you will find the following parameters

• nr (integer) –> total number of radial grid points
• nth (integer) –> total number of angular grid points
• mls (integer) –> maximum number of employed Legendre polynomials for the expansion in theta
• rhalf (double) –> end of the inner radial grid/beginning of the outer grid
• rmax (double) –> end of outer (radial) grid
• planar_symmetry (logical) –> employing symmetry through neglecting odd harmonics
• qfactor (double) –> damping factor for the metric quantities during iteration
• abs_tol (double) –> tolerance when solution is considered to be converged
• verbose (logical) –> determines if the output is put on the screen
• wait_iters (integer) –> number of iterations before checking for convergence after hydro relaxation

And the following constants are used:

• nm (double) = 8.42335d-58 –> neutron mass given in Msun
• rhon (double) = 4.339d-4 –> nuclear saturation density given in Msun^-2
• km_to_msol (double) = 0.677218135d0 –> conversion from km to solar masses

While it isn't to be expected that you need to change the overall constants, it might be worth changing some of the iteration parameters. For this purpose, let us consider running the example for the computation of the non-barotropic configuration and let's vary the following parameters

nr = 4000
nth = 15
mls = 10

which leads to a setup with mass of 2.151388177700834 Msun, but if we increase the resolution

nr = 15000
nth = 100
mls = 50

we get 2.1513872961030418Msun, but have to wait much longer. It might also be of interest for you to change the outer boundary location and see which effect this might have on the overall accuracy of the solution.

Another useful feature of ASWNS is the existence of a doxygen documentation. To create these, please first install doxygen, and then run it via

 sudo apt-get install doxygen
  doxygen

This creates HTML pages on which the functions are defined and also additional definitions of variables are given.