modularsnf 0.4.0

A Python module for Smith Normal Form calculations over Z/N rings

Smith Normal form of Integer matrices mod N (Storjohann)

This is a Python module that follows the deterministic algorithms presented in Arne Storjohann's PhD Dissertation Algorithms for Matrix Canonical Forms (ETH No. 13922, 2000).

It implements the Lemmas and subsequent subroutines that are necessary for calculating the SNF without exponential intermediate values.

It validates against SymPy using a known equivalence between calculating the Smith Normal form of an integer matrix, and then taking mod N, compared to solving it natively in the ring.

Quick Start

from modularsnf import smith_normal_form_mod

S, U, V = smith_normal_form_mod([[2, 4, 0],
                                  [6, 8, 3],
                                  [0, 3, 9]], modulus=36)
# S = U @ A @ V  (mod 36)
# S, U, V are plain Python list[list[int]].

S is the diagonal Smith Normal Form, U and V are unimodular transforms over $\mathbb{Z}/N\mathbb{Z}$. The return order (S, U, V) — diagonal first — follows the SymPy / SageMath convention. Rectangular matrices are supported; S, U, V shapes match the input dimensions.

A matrix is unimodular over $\mathbb{Z}/N\mathbb{Z}$ when $\gcd(\det(M),, N) = 1$, the modular analogue of $|\det(U)| = 1$ over $\mathbb{Z}$.

Lower-level API

For direct access to RingMatrix objects:

from modularsnf.ring import RingZModN
from modularsnf.matrix import RingMatrix
from modularsnf.snf import smith_normal_form

ring = RingZModN(12)
A = RingMatrix(ring, [[2, 4], [6, 8]])
U, V, S = smith_normal_form(A)   # note: (U, V, S) order

For details on the algorithm (band reduction, diagonalization, Storjohann's lemmas), see docs/algorithm.md.

Development Workflow (modern Python)

This repository supports both standard pip workflows and uv workflows.

Using uv

uv venv
uv sync --extra dev
uv run pytest
uv run ruff check .

Using pip

python -m venv .venv
source .venv/bin/activate
pip install -e .[dev]
pytest
ruff check .