Output and diagnostics

run_fdtd returns the final simulation state. Detector results are held in the associated detector-state mapping and are keyed by the detector output names.

Visual inspection

• plot_setup / plot_setup_from_side: object placement and simulation bounds.

• plot_material / plot_material_from_side: rasterized material slices.

• plot_field_slice / plot_field_slice_component: scalar or component field slices.

Always inspect the rasterized scene, not only the intended continuous geometry. At coarse resolution a narrow gap or polygon edge can disappear.

Portable volume output

• export_vti writes uniform-image VTK data.

• export_vtr writes rectilinear-grid VTK data.

• export_arrays_snapshot_to_vti exports arrays from a state snapshot.

• export_stl writes compatible geometry surfaces.

VTK output can be opened in ParaView for volume slices, vector glyphs, and animation.

Spectral data

Convert JAX arrays to NumPy only after the compiled/differentiated calculation:

import numpy as np

spectrum = np.asarray(detector_state["flux"])
np.savez_compressed(
    "spectrum.npz",
    wavelength_m=wavelengths,
    transmission=spectrum,
)

Record units, propagation sign, phasor convention, source normalization, reference plane, grid spacing, runtime, and commit. A bare array is not a reproducible optical result.

Useful scalar diagnostics

• finite-field and finite-gradient assertions;

• peak and residual energy;

• \(R+T+A\) for layered media;

• closed-surface radiated power;

• incident calibration and passive output-power sum;

• best-so-far objective and gradient norm;

• error change under grid refinement.