# fdfd

::: meanas.fdfd

## Core operator layers

::: meanas.fdfd.functional

::: meanas.fdfd.operators

::: meanas.fdfd.solvers

::: meanas.fdfd.scpml

::: meanas.fdfd.farfield

## SCPML conventions

`stretch_with_scpml` now uses `-1` for the low-index face and `+1` for the
high-index face, matching CPML and propagation conventions. It returns copied
widths by default; pass `copy=False` to request mutation explicitly.

Both SCPML builders accept `kappa_function(depth)` for real stretching and
`max_imag_ratio` to limit the final dimensionless `abs(Im(s))/Re(s)`. Start a
mode-solver convergence study with `max_imag_ratio=1.0`: overly strong imaginary
stretching can produce above-light-line PML artifacts. The cap is not a general
spectral guarantee, and weaker absorption can increase boundary reflections.
Check domain size, PML thickness, strength, mode localization, and residuals.
The general scattering profile remains uncapped by default.