These are the API reference docs, generated by FORD from the !!
docstrings in the Fortran source. They describe every module, derived type
and procedure in the solver.
For the user guide — theory, discretisation, vertical coordinates, the pressure-gradient forms, closures, running simulations, the Python driver and the validation suite — see the Sphinx site, which is maintained separately from this reference.
The repository map and run lifecycle are in
docs/codebase/INDEX.md;
the god-state slot map and the four design rules are in
src/core/ocean/README.md.
Acronyms and concept definitions are in
docs/codebase/CONCEPTS.md.
Which closure is enabled and its tunable knobs:
docs/CLOSURE_MATRIX.md
(drift-checked against the code by tools/check_closure_matrix.py).
Most of Roundabout’s code was written by Claude, Anthropic’s AI model, working through Claude Code. Claude was chosen simply because it is what the author had and pays for. The baseline design is the author’s: the architecture, the API, the memory model and the parallelism model, all designed by Jorge Luis Gálvez Vallejo.
Roundabout makes no claim to be a novel implementation of a general circulation model. It is an LLM-driven, human-supervised experiment in taking a general circulation model to GPUs.
In the author’s words:
I (Jorge) acknowledge that no work here is claiming to be novel. It is a porting endeavor, with four aims:
- to explore the role of agents in GPU porting;
- to show Fortran as a viable, modern language for GPU-accelerated, portable scientific code;
- to provide example codebases in modern Fortran for LFortran compiler development;
- to support the wider Fortran community.
If a reference is missing, that is not malicious in any way, shape or form. It is human error, and it will be addressed when someone brings it up.
Because of this, the licensing of this code is MIT.
The parts ported from MOM6 and SIS2 are used and modified under the
Apache License 2.0, as set out in NOTICE.
The numerical methods in Roundabout were developed at NOAA’s Geophysical
Fluid Dynamics Laboratory (NOAA-GFDL); Roundabout adapts them to GPUs. The
ocean dynamical core follows MOM6 and
the sea-ice component follows SIS2.
Full credit for the numerics goes to the MOM6 and SIS2 developers. MOM6 is
also Roundabout’s physics oracle: its behaviour is the reference
Roundabout is checked against, and deliberate divergences are documented in
docs/CLOSURE_MATRIX.md.
Roundabout is a hobby project, written for fun and as the author’s learning project. The author is part of MOM6-GPU, the effort to port MOM6 to GPUs. Roundabout runs in parallel to, and separately from, that work and the GPU porting efforts at NOAA-GFDL and ACCESS-NRI, and it is not part of them.
MOM6 and SIS2 are licensed under the Apache License 2.0, and the ported code
is used and modified under it (see
NOTICE). The
docstrings in this reference cite the paper behind each algorithm, and the
full reference list is in
rdb_docs/source/references.rst.