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:

  • an NSE solver

  • thermal / plasma neutrino losses

  • StarLib and TemperatureTabular rates

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 (providing \(dY/dt\) and the energy loss due to weak rate neutrinos) and Jacobian. It is meant to be used in an application code that provides its own time integrator.

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++20 compiler is required

This will output the following files:

  • actual_network.H : this provides the nuclei masses, 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.

  • approximate_rates.H : the functions that evaluate AproximateRate rates.

  • 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.

  • derived_rates.H : the functions that evaluate rates recomputed via detailed balance.

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

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

  • interp_tools.H : functions used for interpolating partition functions and rates.

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

  • modified_rates.H : the functions that evaluate ModifiedRate rates.

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

  • partition_functions.H : data and functions used for interpolating partition functions.

  • rate_type.H : the core struct used for holding rate evaluations

  • 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.

  • table_rates.H : the data and functions for interpolating tabular rates.

  • 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, including the \(dY/dt\) terms, the individual rates evaluations (without density or composition terms) and the weak-rate neutrino energy loss term. 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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