AMReX Astro Microphysics Networks

pynucastro can generate a C++ network that works in the AMReX-Astro Microphysics. This is done through the AmrexAstroCxxNetwork class. A simple C++ 3-alpha network that works with Microphysics can be created via:

import pynucastro as pyna

reaclib_library = pyna.ReacLibLibrary()

mylib = reaclib_library.linking_nuclei(["he4", "c12", "o16"])

net = pyna.AmrexAstroCxxNetwork(libraries=[mylib], rate_params=[r])

The C++ network uses a set of template files in pynucastro/templates/amrexastro-cxx-microphysics/ which have placeholders of the form <func>(num). Here,

  • func is a tag that corresponds to a function that will be called to write the output in this location

  • num is the number of indentations for that line of code

In BaseCxxNetwork, there is a dictionary of function tags and the corresponding function called ftags. Any network class that derives from this can add to this list to specialize the output.

When the network is written, each template file is read and output line by line, injecting the code output by a function if the line has a function tag in it.

For the generation of the righthand side of the network itself, we use SymPy to build up an expression for each term and then use SymPy’s cxxcode function to translate it into C++ code.

This will directly write out the C++ code into a collection of headers and source files. These are:

  • actual_network.H

    This header simply stores the number of rates, and separately the number of ReacLib and tabular rates, as well as defines the arrays that hold the rate data.

  • actual_rhs.H

    This defines the function to compute the energy release from the network as well as evaluate the rates and construct the “ydot” and Jacobian terms. Function tags are used to compute the screening factors, compute the tabular rates, and build the ydot and Jacobian, and include any plasma neutrino losses.

  • reaclib_rates.H

    This computes the ReacLib reaction rates, with a function provided for each rate.

  • table_rates.H

    This manages reading in tabular rates. It has function tags to define how many tables there are as well as declare the memory for storing the tables.

  • tfactors.H

    This stores the struct that holds the different temperature factors used in the reaction rates.

There are 2 C++ files that are essentially used to define the global arrays.

  • actual_network_data.cpp

  • table_rates_data.cpp

Finally, there are a few meta-data files:


    This lists the nuclei in the network and their properties in a format that Microphysics requires.

  • Make.package

    This is a stub for the build system that list the files needed to build the network.

  • _parameters

    This lists the runtime parameters that affect the network.

To test the library, you can use the unit tests in Microphysics/unit_test/, for example, test_react.