flowrs-dsp
Copyright 2024-2026 David Charlot and the flowRS contributors

Licensed under either of the Apache License, Version 2.0 (LICENSE-APACHE) or the MIT
license (LICENSE-MIT), at your option. This crate is part of flowRS.

Third-party material:

Ports from SciPy (BSD-3-Clause, LICENSES/SciPy-BSD-3-Clause.txt):

    SciPy, Copyright (c) 2001-2002 Enthought, Inc. 2003, SciPy Developers.

  - src/filters.rs: Cascade::filtfilt and its section seeding (scipy.signal.sosfiltfilt,
    sosfilt_zi) and odd_ext (scipy.signal._arraytools.odd_ext);
  - src/elliptic.rs: ellipdeg (scipy.signal._filter_design._ellipdeg) and asne
    (scipy.signal._filter_design._arc_jac_sn);
  - src/filters.rs: the Bessel pole table, values computed with scipy.signal.besselap.

SciPy and NumPy are also the oracles the designers are checked against
(tools/verify_filters.py in flowRS): values in the tests come from running them.

Methods implemented from published sources, with no code taken: the real-argument Jacobi
functions by the arithmetic-geometric mean and the complex-argument addition theorems
(Abramowitz & Stegun, Handbook of Mathematical Functions, 16.4 and 16.21); the elliptic
pole and zero placement (Sophocles J. Orfanidis, Lecture Notes on Elliptic Filter Design,
Rutgers University, 2006); the biquad formulas (Robert Bristow-Johnson, Audio EQ
Cookbook); spectral-flux onset detection (Bello et al., 2005).