To run the simulations, you will first need to download and install Castro by following the instructions on https://amrex-astro.github.io/Castro/docs/getting_started.html

Don't forget to add the home directory to your path using the following command.

  export CASTRO_HOME="/path/to/Castro/"

Note: You must export the path to CASTRO_HOME and not a different name unless you want to modify the name in the makefile.

Once you have completed the above steps, download and extract the specific simulation directory that you want to run from this repository.

Steps to run:

1. Open the downloaded problem directory.

2. Open the terminal inside the directory and type make in the command line. (without the quotations)

3. Now, the code will start to compile.

4. Once the compilation is done, run the following command to start the simulation:

     mpirun -np n ./Castro1d.gnu.MPI.ex inputs_1d
   

   (replace "n" with the number of processors you want to use)

5. Wait till the simulation ends.

Castro outputs in boxlib format, which is not easy to read with the usual tools (especially the 1D datasets cannot be plotted with AmrVis, visit, ParaView and other plotting tools). So, we use a tool called yt to read the files and plot the data. We have provided a Jupyter notebook that you can use to visualize the data using yt. You will first need to install yt in your Python environment. Refer to the following guide for installation:

https://yt-project.org/doc/installing.html

Now, you are all set to run cool simulations of the cold collapse of massive, spherically symmetric and homogenous cold clouds (Newtonian) and compare the results with the GR version of the same.

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Additional notes: Simulations of bounce using a polytropic equation of state

Polytropic equations of state ($P = K \rho^\gamma$) are a good approximation to model neutron stars with only 2 parameters. We use this with values of gamma ranging from $\gamma$ = 2 to 3 to model our cloud reaching neutron degeneracy and bouncing back.

To use the polytropic equation of state:

1. Set EOS_DIR := polytrope in GNUmakefile, which sets the EOS directory in $(MICROPHYSICS_HOME)/EOS.

2. At the bottom of the inputs_1d file, add the following:

     eos.polytrope_gamma = 2.5
     eos.polytrope_K = 1e-2
   

   Note that these values are just given as an example and can be changed as suitable.

3. Follow the steps 2 to 6 in the "steps to run".