zoomy-amrex

AMReX backend for Zoomy — a block-structured AMR finite-volume solver for the shallow-water / shallow-moment family, driven by code generated from a zoomy_core SystemModel.

Model  ──▶  SystemModel  ──▶  AMReX device code  ──▶  AmrCore FV solver
(zoomy_core)              (zoomy_amrex.transformation)   (Source/*.cpp,*.H)

• zoomy_amrex/transformation/ — the backend-owned code printer (the jax backend owns its printer the same way). AmrexSystemModelPrinter emits Model.H from a frozen SystemModel; Numerics.H comes from zoomy_core's AmrexNumerics (a Riemann scheme over the same SystemModel). All "placeholder" kernel functions (conditional, clamp_*, eigensystem, compute_derivative, …) are mapped in the printer's c_functions; the opaque ones resolve to hand-written helpers in the generated UserFunctions.H. The CFL wave speed is Numerics::local_max_abs_eigenvalue (a real Max(|λ_i|) kernel emitted by core's AmrexNumerics, Gershgorin row-sum when eigenvalues=None).
• Source/ — the hand-written C++ driver: ZoomyAmr.cpp (AmrCore: multi-level AMR, subcycling, FillPatch, RK1/SSP-RK2), make_rhs.H (MUSCL/minmod reconstruction, path-conservative D± fluxes, a per-cell implicit-source Newton solve), consuming the generated Model:: / Numerics:: device functions. The driver is generic in Model::n_dof_q (works for any moment level).
• build.py — in-tree driver (the analogue of jax's solver.solve / foam's create_model.py): SystemModel → headers → make → run.
• deliverable.py — reproducible figure/GIF from the AMReX plotfiles.

SIF=.../zoomy_amrex_latest.sif          # AMReX at /opt/amrex, mpicxx, python3
apptainer exec --bind <ZOOMY>:/work $SIF bash -lc '
  export PYTHONPATH=/work/library/zoomy_core:/work/library/zoomy_amrex
  cd /work/library/zoomy_amrex
  python3 build.py --model SWE --dim 2 --ncell 100 --tend 0.1 --order 2 \
      --build-dir /tmp/run --make --run
  python3 deliverable.py /tmp/run/Exec --out /tmp/run/figures/dam_break
'

--model SME --dim 3 --level N generates and builds the N-moment shallow-moment model (state grows with the level; the driver is dof-generic).

Or build the committed Exec/ directly (headers in Source/ are pre-generated for 2-D SWE): cd Exec && make -j && ./main3d.gnu.MPI.ex inputs.

See the steward task files (0025–0028) for the remaining plan.