Design of lvn package
The DP/APT Langevin-equation integrator package is fundamentally a C++ code base with Python support modules, all bundled into a pip-installable package,
Core C++
This C++ is split into three groups, with files in each group denoted by one of the following prefixes:
(1) langevin_;
(2) dplangevin_;
(3) sim_dplangevin_.
The code itself can be found here and its Python wrapping is located here;
detailed documentation, auto-generated by Doxygen, is available
here.
langevin
The cplusplus/langevin_* source files provide the base BaseLangevin class that implements the operator-splitting integration method in a fairly general fashion. Grid geometry and topology, boundary conditions, initial conditions, the integration scheme, and a general form of the Langevin equation are all coded here. The core Dornic-style integrator is a heavily altered version of the Villa-Martín and Buendía code.
dplangevin
The cplusplus/dp/dplangevin_* files define this DPLangevin integrator class. They inherit the general BaseLangevin integrator class and implement several methods left undefined by that parent; most important, they define methods implementing the particular functional form of the directed-percolation Langevin equation and its corresponding nonlinear, deterministic integration step in the split operator scheme.
Other types of absorbing-phase transition-type Langevin equation could be
implemented with alternate subclasses of BaseLangevin and alternate
versions of the SimDP class.
sim_dplangevin
The cplusplus/dp/sim_dplangevin_* files provide a SimDP class, made available through the wrapper at the Python level, required to manage and execute DP Langevin model integration. This SimDP class instantiates a DPLangevin class integrator to do the hard work of numerical integration of the stochastic differential equation. Langevin field density grids are returned to Python (via the wrapper) as numpy arrays,
as are time series of the mean density field and its corresponding epochs.
Wrapping
To make the core C++ code accessible to Python, there is a wrapper file called cplusplus/dp/wrapper_dplvn.cpp.
It uses pybind11 to link the C++ code to a Python runtime via a class instance.
Python support modules
The lvn package includes several Python modules to support
use of the core C++-based integrator.
They are grouped into a set of base modules,
located in the
base folder,
and a set of DP-application modules, which can be found in the companion
dp folder.
In addition, Python scripts and related Jupyter notebooks are provided to help run DP-type Langevin simulations (documented here).
The base modules are:
The DP-specific modules are: