solver_state_t Derived Type

Configuration object (copy of the parsed input). Access physics, grid bounds, BC types, scheme names, etc. via state%cfg%.

Per-rank interior count (= decomp%n_local at runtime). For FDM this is a node count (= cfg%n_cell+1 at -np 1); for FVM a cell count (= cfg%n_cell).

Total global interior count across all ranks (= decomp%n_global). FDM: cfg%n_cell+1 (nodes); FVM: cfg%n_cell (cells). Used to normalise the global L2 residual norm in compute_resid_glob.

Grid metric layer (node coordinates + dx/dξ Jacobian). Built by init_from_config (global) and allocate_work_arrays (local slice).

Per-rank decomposition descriptor. Populated by solver_runtime at session init (Task 6 of the Phase B plan); read by halo_exchange, boundary_conditions, and any other rank-aware code path. At -np 1 this defaults to a single-rank, self-contained decomposition.

Per-block discretization metadata (method + cell count). A single block spans the whole 1D domain today; blocks(1) % method selects the residual path via internal select case in spatial_discretization. Populated by init_from_config once cfg is available.

Current time step size Δt [s]. Initialised from cfg%dt; updated each step by CFL control or last-step clipping.

Global L2 residual norm, updated at the end of every time step.

True when periodic BCs are active (set by apply_bcs()).

Procedure pointer to the active nonlinear reconstruction scheme. Set by init_recon_scheme(); null until then.

Procedure pointer to the smooth-region reconstruction used by hybrid mode. For schemes without a dedicated smooth-region companion, this is bound to the same procedure as @p reconstruct.

Procedure pointer to the active flux-splitting scheme (FVS path). Set by init_flux_scheme(); null when a FDS scheme is active.

Fused flux-splitting procedure that computes F^+ and F^- in one call. Avoids extracting primitives twice per cell in the FVS precompute loop. Set by init_flux_scheme() alongside flux_split; null for FDS schemes.

Procedure pointer to the active FDS approximate Riemann solver. Set by init_flux_scheme(); null when a FVS scheme is active.

Active reconstruction stencil width. Examples: WENO5 = 5, WENO-CU6 = 6, WENO11 = 11.

Left-biased stencil start offset relative to the face index. For example, WENO5 uses -3 so the left-biased stencil starts at iface-3 and covers columns iface-3 : iface+1.

Halo width: number of additional cells on each side of a rank's interior region that must be exchanged from neighbours to drive the reconstruction stencil. Sized by the chosen scheme's stencil metadata (determined by init_recon_scheme).

When .true., spatial_discretization applies K^{-1}/K projection around the reconstruct() call. Set by init_recon_scheme() based on char_proj.

True when a FDS scheme (AUSM+, HLL, HLLC, Roe) is active. When false the FVS path via flux_split is used.

Conserved variables Q_i (neq × n_pt).

Numerical flux at cell faces (neq × (n_pt+1)).

Spatial residual R(Q) (neq × n_pt).

Positive split flux F^+ (neq × n_pt).

Negative split flux F^- (neq × n_pt).

Accumulated wall-clock timers; populated only when cfg%do_timing is .true..

Scratch array 1 (neq × n_pt): stage save for SSPRK22, TVD-RK3, RK4, SSPRK54. Pre-allocated once to avoid per-step heap allocations in the time loop.

Scratch array 2 (neq × n_pt): second stage save for RK4 (k_sum) and SSPRK54 (ub_stage2).

Third RK stage-save scratch (ssprk54: holds u3; the L(u3) residual stays in resid, with its final-stage piece accumulated early).

True after the first bdf2_step() call (bootstrap complete).

Q^{n-1} storage for BDF2. Allocated lazily on first bdf2_step() call.

Rank-0-owned gather buffer for write_solution_file / write_snapshot. Shape (neq, n_pt_global) on rank 0; (neq, 0) on every other rank. Allocated by allocate_work_arrays once decomp is known and reused on every writer call to avoid per-call alloc/dealloc churn.