Functions

April 1, 2026 · View on GitHub

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AntroPy is a Python package for computing entropy and fractal dimension measures of time-series. It is designed for speed (Numba JIT compilation) and ease of use, and works on both 1-D and N-D arrays. Typical use cases include feature extraction from physiological signals (e.g. EEG, ECG, EMG), and signal processing research.

  • Documentation <https://raphaelvallat.com/antropy/>_
  • Changelog <https://raphaelvallat.com/antropy/changelog.html>_
  • GitHub <https://github.com/raphaelvallat/antropy>_

Functions

Entropy

.. list-table:: :widths: 35 65 :header-rows: 1

    • Function
    • Description
    • ant.perm_entropy
    • Permutation entropy — captures ordinal patterns in the signal.
    • ant.spectral_entropy
    • Spectral (power-spectrum) entropy via FFT or Welch method.
    • ant.svd_entropy
    • Singular value decomposition entropy of the time-delay embedding matrix.
    • ant.app_entropy
    • Approximate entropy (ApEn) — regularity measure sensitive to the length of the signal.
    • ant.sample_entropy
    • Sample entropy (SampEn) — less biased alternative to ApEn.
    • ant.lziv_complexity
    • Lempel-Ziv complexity for symbolic / binary sequences.
    • ant.num_zerocross
    • Number of zero-crossings.
    • ant.hjorth_params
    • Hjorth mobility and complexity parameters.

Fractal dimension

.. list-table:: :widths: 35 65 :header-rows: 1

    • Function
    • Description
    • ant.petrosian_fd
    • Petrosian fractal dimension.
    • ant.katz_fd
    • Katz fractal dimension.
    • ant.higuchi_fd
    • Higuchi fractal dimension — slope of log curve-length vs log interval.
    • ant.detrended_fluctuation
    • Detrended fluctuation analysis (DFA) — estimates the Hurst / scaling exponent.

Installation

AntroPy requires Python 3.10+ and depends on NumPy (≥ 1.22.4), SciPy (≥ 1.8.0), scikit-learn (≥ 1.2.0), and Numba (≥ 0.57).

.. code-block:: shell

# pip
pip install antropy

# uv
uv pip install antropy

# conda
conda install -c conda-forge antropy

Development installation

.. code-block:: shell

git clone https://github.com/raphaelvallat/antropy.git
cd antropy
uv pip install --group=test --editable .
pytest --verbose

Quick start

Entropy measures

.. code-block:: python

import numpy as np
import antropy as ant

np.random.seed(1234567)
x = np.random.normal(size=3000)

print(ant.perm_entropy(x, normalize=True))
print(ant.spectral_entropy(x, sf=100, method='welch', normalize=True))
print(ant.svd_entropy(x, normalize=True))
print(ant.app_entropy(x))
print(ant.sample_entropy(x))
print(ant.hjorth_params(x))             # mobility in samples⁻¹
print(ant.hjorth_params(x, sf=100))     # mobility in Hz
print(ant.num_zerocross(x))
print(ant.lziv_complexity('01111000011001', normalize=True))

.. parsed-literal::

0.9995              # perm_entropy        (0 = regular, 1 = random)
0.9941              # spectral_entropy     (0 = pure tone, 1 = white noise)
0.9999              # svd_entropy
2.0152              # app_entropy
2.1986              # sample_entropy
(1.4313, 1.2153)    # hjorth (mobility, complexity)
(143.1339, 1.2153)  # hjorth with sf=100 Hz
1531                # num_zerocross
1.3598              # lziv_complexity (normalized)

Fractal dimension

.. code-block:: python

print(ant.petrosian_fd(x))
print(ant.katz_fd(x))
print(ant.higuchi_fd(x))
print(ant.detrended_fluctuation(x))

.. parsed-literal::

1.0311    # petrosian_fd
5.9543    # katz_fd
2.0037    # higuchi_fd   (≈ 2 for white noise)
0.4790    # DFA alpha    (≈ 0.5 for white noise)

N-D arrays

Some functions accept N-D arrays and an axis argument, making it easy to process multi-channel data in a single call:

.. code-block:: python

import numpy as np
import antropy as ant

# 4 channels × 3000 samples
X = np.random.normal(size=(4, 3000))

pe   = ant.perm_entropy(X, normalize=True, axis=-1)          # shape (4,)
mob, com = ant.hjorth_params(X, sf=256, axis=-1)             # shape (4,) each
nzc  = ant.num_zerocross(X, normalize=True, axis=-1)         # shape (4,)
se   = ant.spectral_entropy(X, sf=256, normalize=True)       # shape (4,)

Performance

Benchmarks on a MacBook Pro M1 Max (2021):

.. list-table:: :widths: 32 20 20 28 :header-rows: 1

    • Function
    • 1 000 samples
    • 10 000 samples
    • Complexity
    • ant.perm_entropy
    • 24 µs
    • 87 µs
    • O(n) ¹
    • ant.spectral_entropy
    • 141 µs
    • 863 µs
    • O(n log n) ⁴
    • ant.svd_entropy
    • 35 µs
    • 140 µs
    • O(n·m²) ²
    • ant.app_entropy
    • 1.5 ms
    • 45.9 ms
    • O(n²) worst ⁵
    • ant.sample_entropy
    • 917 µs
    • 46.0 ms
    • O(n²) worst ⁵
    • ant.lziv_complexity
    • 241 µs
    • 25.2 ms
    • O(n²/log n)
    • ant.num_zerocross
    • 2.5 µs
    • 6 µs
    • O(n)
    • ant.hjorth_params
    • 19 µs
    • 44 µs
    • O(n)
    • ant.petrosian_fd
    • 6 µs
    • 14 µs
    • O(n)
    • ant.katz_fd
    • 9 µs
    • 22 µs
    • O(n)
    • ant.higuchi_fd
    • 7 µs
    • 92 µs
    • O(n·kmax) ³
    • ant.detrended_fluctuation
    • 99 µs
    • 1.4 ms
    • O(n log n)

¹ perm_entropy: O(n) for order ∈ {3, 4} (default), O(n·m·log m) for order > 4. ² svd_entropy: m = order (default 3). ³ higuchi_fd: kmax = max interval (default 10). ⁴ spectral_entropy: O(n log n) for FFT method, O(n) for Welch with fixed nperseg (default). ⁵ app_entropy / sample_entropy: O(n²) worst case, empirically ~O(n^1.5) via KDTree average case.

Numba functions (sample_entropy, higuchi_fd, detrended_fluctuation) incur a one-time compilation cost on the first call.

Contributing

AntroPy was created and is maintained by Raphael Vallat <https://raphaelvallat.com>. Contributions are welcome — feel free to open an issue or submit a pull request on GitHub <https://github.com/raphaelvallat/antropy>.

Note: this program is provided with NO WARRANTY OF ANY KIND. Always validate results against known references.

Acknowledgements

Several functions in AntroPy were adapted from:

  • MNE-features <https://github.com/mne-tools/mne-features>_ — Jean-Baptiste Schiratti & Alexandre Gramfort
  • pyEntropy <https://github.com/nikdon/pyEntropy>_ — Nikolay Donets
  • pyrem <https://github.com/gilestrolab/pyrem>_ — Quentin Geissmann
  • nolds <https://github.com/CSchoel/nolds>_ — Christopher Scholzel