Working and verified version of multilevel atom susceptibility.

[acerjan]

This is the version of the code that is verified with SALT, as we discussed in the issue.

[stevengj]

Great! Ideally you can also include documentation in the PR, including specification of precisely what equations are implemented and the definitions of the parameters. (Note that the markdown documentation can include LaTeX equations.)

[stevengj]

@oskooi suggested that we merge this now so that we can start playing with it and work on adding a Python front-end.

@acerjan, can you make a separate PR for documentation?

[stevengj]

We also need a PR for a regression test to make sure that this doesn't bit-rot. That could be as simple as running one of your 1d test cases and adding a check for the numbers that you have already validated.

[acerjan]

I'm working on the documentation now, and I can put together a separate PR, sure. it took a while to get mkdocs running correctly.

I understand conceptually what you want by a regression test, but I'll need a bit more guidance as to where this goes in the package. Can you point me in the direction of the other tests?

[oskooi]

The C++ tests are in tests/ and the Python tests in python/tests/. A Python test would be sufficient but we need to add the front end first (which we are working on now). @ChristopherHogan can help you port the existing Scheme multilevel example to Python as a unit test.

[oskooi]

For reference, here are the commands to install and run mkdocs in a separate Conda environment for viewing the Meep documentation via a local web server:

conda create -n md -c conda-forge mkdocs python-markdown-math
source activate md
pip install --user mkdocs-material
cd /path/to/meep/
mkdocs serve
source deactivate

[acerjan]

For the documentation, I've written the general theory along with some verification plots into Materials.md. Are there additional locations where you'd like for me to provide documentation? Will you be writing documentation for the scheme and python interfaces?

[oskooi]

Please also update the Scheme tutorial example as necessary with additional information based on the recent changes. We will port this tutorial to Python and also provide documentation for the interface.