Relationship & diff between models/s4/s4.py & src/models/sequence/kernels/ssm.py

[jchia]

I understand that models/s4/s4.py is a standalone file that can be taken on its own to use the S4 models, not counting the CUDA kernel module. I have some questions about its intent and nature relative to the code in src/models/sequence/kernels/

Is it the case that models/s4/s4.py is provided mainly for convenience and ease-of-use from having just one source file, and that it is not meant to have all the features available from src/models/sequence/kernels/ssm.py?

In terms of the development process, is it the case that models/s4/s4.py is downstream of src/models/sequence/kernels so that changes go to the latter first and then get manually ported to the former?

In terms of software behavior (the values that are calculated mathematically ignoring floating-point error and random seed differences), is models/s4.py meant to do the same thing as src/models/sequence/kernels/ssm.py for the use cases that it covers?

Which version (standalone vs non-standalone) of the S4 implementation is generally used for the experiments in the papers?