# code

Plant model, controllers, and reach-analysis toolchain for the
HAHACS preliminary example. All Julia.

## What this is

A 10-state coupled neutronics + thermal-hydraulics model (point kinetic
equations + lumped thermal loop) with continuous-mode controllers for
each of the DRC modes (shutdown, heatup, operation, scram), plus a
hand-rolled linear reach-tube propagator, a Lyapunov-ellipsoid barrier
attempt, and scaffolding for TMJets-based nonlinear reach.

Ported from MATLAB on 2026-04-20 once the reach experiments made it
clear that Julia's stack (`OrdinaryDiffEq`, `MatrixEquations`,
`ReachabilityAnalysis`, `LazySets`, `@taylorize`) was the right tool
for everything we need going forward. The MATLAB originals are in
the git history.

## Running

First time:

```bash
cd code
julia --project=. -e 'using Pkg; Pkg.instantiate()'
```

Subsequent:

```bash
julia --project=. scripts/main_mode_sweep.jl          # all 5 DRC modes, figures
julia --project=. scripts/reach_operation.jl          # operation-mode linear reach
julia --project=. scripts/barrier_lyapunov.jl         # Lyapunov barrier attempt
julia --project=. scripts/barrier_compare_OL_CL.jl    # OL vs CL barrier
julia --project=. scripts/reach_heatup_nonlinear.jl   # nonlinear heatup (10s cap)
```

Figures save to `../docs/figures/`. Reach results save to
`../reachability/*.mat` (gitignored).

## Structure

See `CLAUDE.md` for the architectural overview and `../journal/` for
the invention-log-style narrative of how this code got written.

## Dependencies

From `Project.toml`:

- `OrdinaryDiffEq` — ODE solver, Rodas5 for stiff systems.
- `MatrixEquations` — `arec` for LQR Riccati, `lyapc` for Lyapunov.
- `ReachabilityAnalysis` + `LazySets` — reach sets and set operations.
- `Plots` — figures (GR backend by default).
- `JSON` — read `../reachability/predicates.json`.
- `MAT` — save results.

`Manifest.toml` is gitignored; regenerate locally on first
`Pkg.instantiate()`.