divergence 1.2.0

Information Theoretic Measures of Entropy and Divergence

Divergence

The Dissolution of Uncertainty — One Bit at a Time

---

Divergence is a Python package for computing information-theoretic measures of entropy and divergence from probability distributions and samples.

In 1948, Claude Shannon published "A Mathematical Theory of Communication", laying the foundation for information theory and giving us a rigorous way to quantify uncertainty. Divergence puts Shannon's toolkit — and the extensions built upon it over the following decades — into your hands.

What You Can Compute

Measure	Discrete	Continuous	What it tells you
Entropy	yes	yes	How much uncertainty a distribution carries
Cross Entropy	yes	yes	The cost of encoding one distribution using another's code
KL Divergence	yes	yes	How much information is lost when approximating one distribution with another
Jensen-Shannon Divergence	yes	yes	A symmetric, bounded measure of distributional difference
Mutual Information	yes	yes	How much knowing one variable tells you about another
Joint Entropy	yes	yes	The total uncertainty in a pair of variables
Conditional Entropy	yes	yes	The remaining uncertainty in one variable after observing another

All measures support configurable logarithm bases: base=np.e (nats, default), base=2 (bits), base=10 (hartleys).

In a Bayesian context, relative entropy can be used as a measure of the information gained by moving from a prior distribution q to a posterior distribution p.

Installation

pip install divergence

Quick Start

import numpy as np
from divergence import entropy_from_samples, relative_entropy_from_samples

# How much uncertainty does this distribution carry?
sample = np.random.normal(0, 1, size=10000)
h = entropy_from_samples(sample, discrete=False)

# How different are these two distributions?
p = np.random.normal(0, 1, size=10000)
q = np.random.normal(0.5, 1.2, size=10000)
kl = relative_entropy_from_samples(p, q, discrete=False)

Explore the Notebook

The interactive Divergence notebook walks through every measure with explanations, historical context, and worked examples — a self-contained introduction to information theory through code.

Development Setup

Requires uv (a fast Python package manager):

git clone https://github.com/michaelnowotny/divergence.git
cd divergence

# Create an isolated virtual environment and install everything
uv venv .venv --python 3.12
source .venv/bin/activate          # Windows: .venv\Scripts\activate
uv pip install -e ".[dev]"

Run the Notebook

./scripts/lab

This script ensures Jupyter Lab runs inside the project's virtual environment with all dependencies correctly installed — no version conflicts, no wrong Python.

Tip: Always launch Jupyter from within the activated .venv environment. Running jupyter lab from a system Python or different environment will fail to find the divergence package.

Run Tests and Linting

pytest                              # All 122 tests (~18s)
pytest tests/test_discrete.py       # Discrete tests only (fast, ~2s)

ruff check src/ tests/              # Lint
ruff format src/ tests/             # Format

References

1. Shannon, C. E. (1948). "A Mathematical Theory of Communication." Bell System Technical Journal, 27(3), 379-423.
2. Kullback, S. & Leibler, R. A. (1951). "On Information and Sufficiency." Annals of Mathematical Statistics, 22(1), 79-86.
3. Cover, T. M. & Thomas, J. A. (2006). Elements of Information Theory, 2nd edition. Wiley.
4. Entropy (information theory) — Wikipedia
5. Kullback-Leibler divergence — Wikipedia
6. Jensen-Shannon divergence — Wikipedia
7. Mutual information — Wikipedia

License

MIT