quatint 0.0.4

A quatint class, for using quaternions backed by integers and half-integers (Hurwitz integers).

quatint

Exact (integer-backed) quaternion arithmetic for the Hurwitz integers.

quatint provides a fast, mypyc-friendly hurwitzint type that behaves like a small, practical numeric object: addition/subtraction/multiplication/power, norms and conjugation, plus left/right Euclidean division, left/right gcd, and deterministic factorization utilities.

Why this exists

Python’s built-in numeric types don’t provide an exact, integer-backed quaternion type—especially not one that can represent the Hurwitz order (a + b i + c j + d k) / 2 without floating point.

quatint keeps everything as integers under the hood while still letting you work with both:

• Lipschitz integers: $a, b, c, d ∈ Z$
• Hurwitz “half” integers: $(a + b i + c j + d k)/2$ with a parity constraint

Key features

• Exact arithmetic (no floats required for quaternion values)
• Hurwitz order representation with parity enforcement
• Non-commutative multiplication
• Reduced norm $N(q) ∈ Z$ and quaternion conjugation
• Euclidean division (norm-Euclidean) via:
  • divmod(a, b) for left-quotient division (a = q*b + r)
  • a.rdivmod(b) (or quatint.rdivmod(a, b)) for right-quotient division (a = b*q + r)
• Left/right gcd (gcd_left, gcd_right) built on the corresponding division
• Deterministic factorization into content, unit, and Hurwitz primes (by prime norms)

Installation

python -m pip install quatint

This project is designed to compile cleanly with mypyc for speed (CI/test setups often ensure the compiled artifact is what’s running).

Quick start

from quatint import hurwitzint

a = hurwitzint(1, 2, 3, 4)
b = hurwitzint(2, 3, 4, 5)

print(a)         # (1+2i+3j+4k)
print(a * b)     # quaternion product (non-commutative)
print(b * a)     # generally different

Half-integers (Hurwitz elements)

Use half=True to provide numerator components of a /2 element:

from quatint import hurwitzint

h = hurwitzint(1, 3, 5, 7, half=True)
print(h)  # (1+3i+5j+7k)/2

Division (left-quotient)

divmod(a, b) defines quotient on the left:

from quatint import hurwitzint

a = hurwitzint(2, 3, 4, 53)
b = hurwitzint(1, 2, 3, 4)

q, r = divmod(a, b)
assert q * b + r == a

Right-division (right-quotient)

Use rdivmod (method or helper) to define quotient on the right:

from quatint import hurwitzint, rdivmod

a = hurwitzint(2, 3, 4, 53)
b = hurwitzint(1, 2, 3, 4)

q, r = rdivmod(a, b)
assert b * q + r == a

GCD (left and right)

Because multiplication is non-commutative, there are two natural gcd notions:

from quatint import hurwitzint

a = hurwitzint(2, 3, 4, 53)
b = hurwitzint(1, 2, 3, 4)

gl = a.gcd_left(b)    # common left divisor (a = gl*x, b = gl*y)
gr = a.gcd_right(b)   # common right divisor (a = x*gr, b = y*gr)

Factorization

Factorization returns a compact normal form:

• content: maximal positive integer scalar dividing the element (in the Hurwitz sense)
• unit: a norm-1 Hurwitz unit (deterministically chosen)
• primes: Hurwitz primes (each with prime rational norm), normalized via unit migration

from quatint import hurwitzint

n = hurwitzint(2, 3, 4, 53)

fr = n.factor_right()
assert fr.prod_right() == n

fl = n.factor_left()
assert fl.prod_left() == n

Representation & guarantees

Internal representation

Values are stored in numerator units:

(A + B i + C j + D k) / 2

This means:

• Lipschitz integers are stored with even numerators.
• True Hurwitz half-integers are stored with odd numerators.
• The constructor enforces the parity constraint.

Scalar coercions

int and float inputs are accepted as scalars and converted via int(...) (i.e., truncation semantics). Quaternion values themselves remain exact.

Public API (high level)

• hurwitzint(a=0, b=0, c=0, d=0, *, half=False)
• hurwitzint.conjugate()
• abs(h) → reduced norm N(h) (an int)
• divmod(a, b) → left-quotient Euclidean division
• a.rdivmod(b) / rdivmod(a, b) → right-quotient Euclidean division
• a.gcd_left(b) / gcd_left(a, b)
• a.gcd_right(b) / gcd_right(a, b)
• a.factor_left() / a.factor_right() → HurwitzFactorization
• HurwitzFactorization.prod_left() / .prod_right()