Spectral `App` configuration reference (JSON / TOML)¶

This page lists the JSON / TOML surface consumed by the default CPU spectral stack (SpectralCpuStack → SpectralSimulationSession → Simulator) when you use pfc::ui::App<Model> (e.g. apps/tungsten, apps/aluminumNew). Apps may add keys or nest objects; treat shipped inputs as ground truth when in doubt.

Pipeline order: app_pipeline.md. Mental model: configuration.md.

Domain (grid)¶

Parsed by from_json<Domain>(settings) — supports flat keys on the root object or nested under "domain".

Key(s)	Type	Meaning
`Lx`, `Ly`, `Lz`	integer	Grid point counts
`dx`, `dy`, `dz`	number	Spacing
`origin` (or `origo`)	string	`"center"` or `"corner"` — sets physical origin convention

Examples: top-level keys in some snippets; tungsten uses a "domain" object with the same logical fields (apps/tungsten/inputs_json/).

Time stepping¶

Parsed by from_json<Time>(settings) — supports flat keys or nested under "timestepping".

Key	Type	Meaning
`t0`, `t1`	number	Integration window
`dt`	number	Step size
`saveat`	number	Output cadence (also gates binary writers in JSON wiring; `≤ 0` disables periodic result writes in the default helper)

FFT (`plan_options`)¶

Object key "plan_options" (JSON) or [plan_options] (TOML). Passed to HeFFTe plan construction on the CPU spectral path. backend: "cuda" is rejected for SpectralCpuStack / CpuFft — use CPU fftw here or a GPU-specific app driver.

Annotated reference file: examples/fft_backend_selection.toml. Tutorial: tutorials/fft_heffte_plan_options.md.

Model¶

Key	Type	Meaning
`model.name`	string	Conventionally matches the app’s model registration
`model.params`	object	Model-specific; optional `from_json` into your C++ params type

Validation is model-dependent (see parameter_validation.md).

Result writers (binary)¶

When saveat > 0 and fields is present, add_result_writers_from_json registers BinaryWriter per entry:

Key	Type	Meaning
`fields[].name`	string	Field identifier known to the simulator / model
`fields[].data`	string	Filename template; if it contains `%`, `printf`-style formatting with the simulator’s output increment is applied (see `binary_field_io_spec.md`)

There is no VTK branch in this helper today.

Initial / boundary conditions¶

Key	Type	Meaning
`initial_conditions`	array	Objects with `type`, optional `target`, type-specific fields
`boundary_conditions`	array	Same pattern

Modifier types must be registered in main before App runs (register_field_modifier<…>). See app_pipeline.md and examples/10_ui_register_ic.cpp.

Optional sections¶

Key	Handled by	Notes
`simulator`	`apply_simulator_section_from_json`	e.g. counter / increment for filenames
`profiling`	`AppProfilingController`	`performance_profiling.md`

TOML vs JSON¶

Same logical keys; TOML uses tables such as [domain], [timestepping], [plan_options], [model], [model.params].

Spectral App configuration reference (JSON / TOML)¶