lightweaver 0.4.0

Non-LTE Radiative Transfer Framework in Python

Lightweaver

C. Osborne (University of Glasgow) & I. Milić (NSO/CU Boulder), 2019-2020

MIT License

Lightweaver is an NLTE radiative transfer code in the style of RH. It is well validated against RH and also SNAPI. The code is currently designed for plane parallel atmospheres, either 1D single columns (wavelength parallelisation in progress) or 1.5D parallel columns with ProcessPool or MPI parallelisation. There is also preliminary support for 2D atmospheres.

Whilst the core numerics are implented in C++, as much of the non-performance critical code as possible is implemented in Python, and the code currently only has a Python interface (provided through a Cython binding module). These bindings could be rewritten in another language, so long as the same information can be provided to the C++ core.

The aim of Lightweaver is to provide an NLTE Framework, rather than a "code". That is to say, it should be more maleable, and provide easier access to experimentation, with most forms of experimentation (unless one wants to play with formal solvers or iteration schemes), being available directly from python. Formal solvers that comply with the interface defined in Lightweaver can be compiled into separate shared libraries and then loaded at runtime. The preceding concepts are inspired by the well-recieved machine learning frameworks such as PyTorch and Tensorflow.

Installation

For most users precompiled python wheels (supporting modern Linux, Mac, and Windows 10 systems) can be installed from pip and are the easiest way to get started with Lightweaver. Lightweaver requires python 3.8+, and it is recommended to be run inside a virtual environment using conda. In this case a new virtual environment can be created with:

conda create -n Lightweaver python=3.8

activate the environment:

conda activate Lightweaver

and Lightweaver can then be installed with

python -m pip install lightweaver

Installation from source

Whilst the above should work for most people, if you wish to work on the Lightweaver backend it is beneficial to have a source installation. This requires a compiler supporting C++17. The build is then run with python3 -m pip install -vvv -e .. The libraries currently produce a few warnings, but should not produce any errors.

Documentation

Documentation is currently lacking, although it is currently being produced. I suggest looking through the samples repository (in particular the Simple*.py) to gain an understanding of the basic functionality and interfaces. These samples are kept as up to date as possible.

Feel free to contact me through this repository if difficulties are encountered.

Acknowledgements

The python implementation of the Wittmann equation of state has been kindly provided J. de la Cruz Rodriguez.