Add models

[znicholls]

Adds two-layer model and impulse response model. Also includes a notebook which goes through the details of why the two-layer and impulse response models are identical.

• [x] Tests added
• [x] Documentation added
• [x] Example added (in the documentation, to an existing notebook, or in a new notebook)
• [x] Description in CHANGELOG.rst added (single line such as: (`#XX <https://github.com/openscm/openscm-twolayermodel/pull/XX>`_) Added feature which does something)

For reference:

• two-layer code already here https://github.com/znicholls/mullet/blob/prototype/sandbox/speed-test-multiple-parameters.py
• impulse response code here https://github.com/OMS-NetZero/FAIR/blob/c189beadf68a14bd18bd7b8b9604ee9b780c8a08/fair/forward.py#L155

[znicholls]

@rgieseke this is ready to have a first look at (there's a bug somewhere, something for later/tomorrow). Probably start with https://github.com/openscm/openscm-twolayermodel/blob/c84c8a4e2b4c6deab077a9f463486e1cf8589c23/notebooks/impulse-response-equivalence.ipynb then go from there during a reivew?

[znicholls]

Minor consistency thing, there are a few variables like lambda_0 or b_pt_1 with underscores before the number, most others without, maybe unify?

Done

[rgieseke]

What is the 't' prefix for variables, just for testing?

[rgieseke]

All green! Should we merge this now?

[znicholls]

Yep t for test.

I will wrangle pylint for 20 minutes, then we can merge.