Module spectral 

Spectral methods — FFT-based PDE solving for periodic domains.

Functions

dft

1D Discrete Fourier Transform (naive O(n²) — for correctness; production uses FFT).

idft

1D Inverse DFT.

power_spectrum

Power spectrum (magnitude² of DFT coefficients).

spectral_heat_step

Solve the 1D heat equation spectrally: u_t = α * u_xx on periodic domain [0, L].