Changelog

Main-branch updates after v1.4.0

These items are already merged on main, but they go beyond the current v1.4.0 package snapshot.

Structured preflight validation via sim.preflight(strict=False/True) to catch common CPML / NTFF / Floquet / PEC setup mistakes before expensive runs.
Expanded cross-validation coverage to a 23-script bundle, including newer helical-antenna, Debye / Drude, CRLH, waveguide-mode, reciprocity, and resonator-Q cases.
PolylineWire geometry support for wire-like structures, plus follow-up far-field fixes around non-uniform-cell area handling.

Waveguide / Floquet differentiable workflows: modal and periodic ports now work inside forward() and optimize().
JAX-differentiable far-field evaluation via compute_far_field_jax() for beam-shaping and radiation-aware optimisation objectives.
NTFF-aware optimize() forward pass — if an objective accepts ntff_box=..., the optimiser now builds and passes the NTFF box for far-field losses.
Time-domain proxy objectives for differentiable optimisation:
- minimize_reflected_energy()
- maximize_transmitted_energy()
Result and dataset export: geometry JSON, experiment reports, simulation datasets, optimisation trajectories, and richer far-field / optimisation save helpers.
Advanced solver additions: experimental ADI 2-D / 3-D paths, SBP-SAT subgridding work, and auto_refine() fixes for smaller grids.

Advanced example bundle under examples/50_advanced/ covering patch bandwidth optimisation, waveguide inverse design, broadband matching, array coupling, dielectric-lens shaping, material characterisation, and a visualization showcase.
GPU validation scripts and follow-up hardening for FFT extraction, physics setup, Floquet / waveguide optimisation, and non-uniform-mesh workflows.

5-case RF validation against published references (patch antenna, WR-90 cutoff, dielectric cavity, microstrip impedance, coupled-line filter).
Convergence-study helpers: convergence_study(), quick_convergence(), and Richardson extrapolation utilities.
gradient_check() for automatic AD vs finite-difference verification.
Memory estimation in auto_configure() (estimated_memory_mb, max_memory_mb).
Kerr nonlinear material support via ADE.
RIS unit-cell workflow for reconfigurable-surface design studies.
Pre-AMR error indicators and training-data export for surrogate workflows.
Mixed precision (float16 field storage) for memory reduction.

GPU speedups from pre-baked coefficients and other kernel improvements.
Configurable multi-GPU ghost exchange interval for better distributed throughput.
Three new tutorials: patch antenna, microstrip filter, and convergence methodology.
Respectful solver-comparison docs for public-facing positioning.

Multi-GPU distributed FDTD via jax.pmap with 1-D slab decomposition.
- Phase 1: PEC boundaries, soft sources, point probes.
- Phase 2: Full CPML support.
- Phase 3: Lumped ports and dispersive Debye/Lorentz/Drude materials.
Core Yee-kernel optimisation with pre-baked update coefficients and fused curl/update paths.
Configurable ghost exchange interval for reduced synchronization overhead.

Distributed benchmark script: examples/33_distributed_benchmark.py.
30 distributed tests plus targeted waveguide, Floquet, and material-fit regression tests.

Conformal PEC (Dey-Mittra) for curved conductors.
Density-based topology optimisation with filtering, projection, and beta continuation.
Differentiable material fitting from measured S-parameters.
Multi-mode waveguide ports with TE/TM eigenmodes.
Floquet ports and Bloch-periodic boundary conditions for unit-cell analysis.
Antenna metrics (gain, efficiency, HPBW, bandwidth, F/B ratio).
Parametric sweeps and jax.vmap batch evaluation.
RF workflow tooling: Smith chart plotting, de-embedding, multi-port Touchstone I/O, PCB stackup builder.
Streamlit dashboard for browser-based exploration.