# fdtd

::: meanas.fdtd

## Core update and analysis helpers

::: meanas.fdtd.base

::: meanas.fdtd.pml

::: meanas.fdtd.boundaries

::: meanas.fdtd.energy

::: meanas.fdtd.phasor

CPML derivatives use electric widths for forward differences and magnetic
widths for backward differences. `cpml_params(..., dx=1.0)` specifies the uniform
physical cell width normal to a face; arbitrary nonuniform PML grading is not
implemented by this constructor. Scale the timestep consistently with the grid.

`ln_R_per_layer` must be finite and strictly negative. Zero attenuation raises
`ValueError`; disable individual CPML faces with `None` in the parameter table
passed to `updates_with_cpml`.