Function vmd 

pub fn vmd(signal: &Signal<f64>, config: &VMDConfig) -> Result<VMDResult>

Decompose signal into config.num_modes band-limited modes via VMD.

Follows the ADMM iteration in Dragomiretskiy & Zosso (2014) §3.2 verbatim, with input mirror-extension matching the reference MATLAB implementation (signal padded to 2N via symmetric reflection, ADMM run on extended signal, central N samples returned).

Errors

• WaveletError::InvalidParameter if num_modes < 1, tolerance ≤ 0, max_iterations == 0, or alpha resolves non-finite.
• WaveletError::SignalTooShort for signals of length < 4.
• WaveletError::NumericError if any input sample is non-finite or the ADMM produces non-finite spectra (indicates an ill-conditioned α).