xact-py

Python wrapper for XAct.jl — a native Julia port of the Wolfram xAct tensor algebra library for general relativity.

Note: All code in this repository is generated by AI. It was built under strict engineering practices but is not warranted to be absolutely correct. See the full disclaimer.

Installation

Install the latest published release from PyPI:

pip install xact-py

On first import, xact-py resolves the Julia package XAct from the Julia registries via juliapkg/juliacall.

If you need unreleased changes from this repository, install from a local checkout in editable mode and point juliapkg at a shared Julia project that develops the local XAct.jl checkout:

git clone https://github.com/sashakile/XAct.jl.git
cd XAct.jl
uv pip install -e packages/xact-py
export PYTHON_JULIAPKG_PROJECT="$PWD/.juliapkg-xact"
julia --project="$PYTHON_JULIAPKG_PROJECT" -e 'using Pkg; Pkg.develop(path=pwd()); Pkg.instantiate()'

Julia is managed automatically via juliacall.

Quick Start

import xact

xact.reset()
M = xact.Manifold("M", 4, ["a", "b", "c", "d"])
T = xact.Tensor("T", ["-a", "-b"], M, symmetry="Symmetric[{-a,-b}]")
xact.canonicalize("T[-b,-a] - T[-a,-b]")  # returns "0"

Features

• Canonicalization — Butler-Portugal algorithm for tensor index canonicalization
• Contraction & Simplification — metric contraction, iterative simplification
• Covariant Derivatives — commutation, sorting, Riemann identities
• Perturbation Theory — multinomial Leibniz expansion, curvature perturbations
• Coordinate Components (xCoba) — basis changes, Christoffel symbols, CTensor
• Riemann Invariants (xInvar) — classification and database of Riemann polynomial invariants
• Variational Calculus — Euler-Lagrange operator, integration by parts

Example: Metric and Curvature

import xact

xact.reset()
M = xact.Manifold("M", 4, ["a", "b", "c", "d", "e", "f"])
g = xact.Metric("g", ["-a", "-b"], M)

# Riemann symmetry: R_abcd + R_abdc = 0
xact.canonicalize("RiemannCD[-a,-b,-c,-d] + RiemannCD[-a,-b,-d,-c]")
# returns "0"

# Simplify a contracted Riemann expression
xact.simplify("RicciCD[-a,-b] - RiemannCD[-a,-c,-b,-d] * g[c,d]")
# returns "0"

Documentation

Full documentation at saxa.xyz/XAct.jl.

License

GPL-3.0 — see LICENSE.