Architecture¶

This page maps the physics onto the C++ code: the top-level class, the module objects it owns, and the flow of control.

Entry point¶

src/model_main/model_main.cpp contains main. It takes the model folder as the single argument, constructs an agb::AGBStarModel, and calls calcModel(). The special argument --selftest instead runs the Henyey structure-solver validation (Jacobian AD-vs-FD, Newton solve, eigenvalue solve, grey bootstrap) and exits.

The top-level model object¶

agb::AGBStarModel (src/agb_model/) owns one instance of each physics module and orchestrates the iteration. The members, in construction order (which is also the dependency order), are:

Member	Class	Role
`config`	`agb::ModelConfig`	Parsed `config.toml`; owns all parameters.
`spectral_grid`	`agb::SpectralGrid`	Wavenumber/wavelength grids and interpolation.
`atmosphere`	`agb::Atmosphere`	The persistent structure (radius, \(T_\mathrm{gas}\), \(T_\mathrm{dust}\), \(\rho\), \(p\), \(v\)), number densities, and all opacity arrays; the equation of state; structure I/O.
`chemistry`	`agb::FastChemChemistry`	Equilibrium gas-phase composition (FastChem).
`dust_species`	`agb::DustSpecies` ⟵ `agb::GailSedlmayrDust`	Dust nucleation/growth (moment method) and dust opacity (Mie).
`transport_coeff`	`agb::TransportCoefficients`	Gas opacities (lines, CIA, H⁻/H₂⁻, Rayleigh).
`radiative_transfer`	`agb::RadiativeTransfer`	Spherical VEF moment radiative transfer; owns the `agb::RadiationField` per shell.
`temperature_correction`	`agb::TemperatureCorrection`	Unsöld–Lucy and full-linearisation correctors.
`hydrodynamics`	`agb::Hydrodynamics`	Wind structure, sonic point, mass-loss rate; optional `agb::StructureSolver` (Henyey).

The modules communicate almost entirely through the shared agb::Atmosphere object (temperatures, density, number densities, opacities) and through the agb::RadiationField (mean intensity, flux, flux-mean extinction). This keeps the interfaces narrow.

Control flow¶

main
└─ AGBStarModel::calcModel                         (outer / global loop)
   ├─ chemistryHydroIteration                      (inner loop)
   │  ├─ chemistryDustIteration
   │  │  ├─ FastChemChemistry::calcChemicalComposition
   │  │  ├─ Atmosphere::equationOfState
   │  │  └─ GailSedlmayrDust::calcDistribution      (carbon-depleting RK4 sweep)
   │  ├─ radiativeTransfer
   │  │  ├─ dust  + gas opacities  (per shell)
   │  │  └─ RadiativeTransfer::solveRadiativeTransfer  (VEF moment method)
   │  ├─ Hydrodynamics::setDustState
   │  ├─ Hydrodynamics::calcWindVelocity            (Melia Φ / shooting / Henyey)
   │  └─ Atmosphere::equationOfState
   ├─ temperatureIteration                          (one RE correction step)
   │  ├─ RadiativeTransfer::solveRadiativeTransfer
   │  ├─ TemperatureCorrection::calculate           (Unsöld–Lucy)   ── or ──
   │  ├─ TemperatureCorrection::linearisedCorrection (full linearisation)
   │  ├─ adaptive damping / Anderson / cap
   │  └─ convergence tests (flux, energy balance, settling)
   └─ applyMovableGrid                              (optional, every N iters)

After the outer loop converges (or hits nb_temperature_iter), the spectrum, structure, dust and hydro outputs are written.

Persistent iteration state¶

agb::AGBStarModel carries the state that must survive across outer iterations: the temperature-iteration counter, the two-phase corrector latch (linearisation_active, linearisation_ready_count), the per-layer relaxation factors and previous corrections (relaxation_gas/dust, prev_delta_b_gas/dust), and the Anderson history (anderson_x_*, anderson_f_*). All of this is reset at the start of calcModel() and (the per-node parts) when the movable grid fires.

Third-party libraries¶

See Installation and building for versions. FastChem (chemistry), LX-MIE (dust Mie theory), Eigen + CppAD (Henyey linear algebra and autodiff), and toml++ (config parsing) are fetched and built by CMake.