Simple C++ network

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Simple C++ network#

A SimpleCxxNetwork is a very basic C++ network. It supports ReacLib rates, approximate rates, and screening (via the method of [Chugunov et al., 2007]).

Important

Currently, the following features are not supported:

  • tabular rates

  • partition functions

  • NSE

  • plasma neutrino losses

A simple C++ network can be created as:

import pynucastro as pyna

rl = pyna.ReacLibLibrary()
lib = rl.linking_nuclei(["he4", "c12", "o16"])

net = pyna.SimpleCxxNetwork(libraries=[lib])
net.write_network()

Note

The SimpleCxxNetwork outputs the righthand side function (\(dY/dt\)) and Jacobian. It is meant to be used in an application code that provides its own time integrator. Furthermore, there is no energy/temperature evolution, but the application code can augment the set of equations being integrated with an energy equation as needed.

Note

A C++17 compiler is required

This will output the following files:

  • actual_network_data.cpp : this contains the initialization function, actual_network_init() and the definitions of the mass and binding energy arrays.

  • actual_network.H : this provides enums to index the rates and a vector of strings that give the rate names.

  • actual_rhs.H : this provides the righthand side function and Jacobian.

  • amrex_bridge.H : a header that defines some of the basic types that we use to store information. It is derived from the AMReX library since we reuse some of the AmrexAstroCxxNetwork code to create a SimpleNetwork.

  • burn_type.H : this is a simple struct, burn_t, that holds thermodynamic data. An application code can add more members to the struct, as needed, to store additional data.

  • fundamental_constants.H : this provides the fundamental constants needed throughout the network.

  • GNUmakefile : a GNU makefile to build the test program.

  • main.cpp : a simple driver that simply evaluates the righthand side and Jacobian for a single thermodynamic state and compute the energy release.

  • network_properties.H : a header providing the properties of the nuclei.

  • reaclib_rates.H : the functions that evaluate the ReacLib reaction rates.

  • screen_data.H : this defines some functions used in precomputing common screening factors.

  • screen.H : the actual implementation of the Chugunov 2007 screening.

  • tfactors.H : a struct that stores the various temperature powers needed to compute reaction rates.

Test driver#

A test driver can be built by simply doing:

make

and run as:

./main

This will simply evaluate the righthand side and Jacobian at a single thermodynamic state and print out the output. It is intended to show how to work with the interfaces provided by pynucastro.

To change the density and temperature, you can pass values as arguments (both must be specified if you are overriding the defaults), e.g.:

./main 100 1.e7

would use \(\rho = 100~\mathrm{g~cm^{-3}}\) and \(T = 10^7~\mathrm{K}\).

By default screening is included. To disable screening, compile as:

make DISABLE_SCREENING=TRUE
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