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raxis

raxis is a from-scratch re-implementation of the core of PyTorch, the ATen tensor library and the autograd engine, in C++20 with Python bindings. It is distilled from the PyTorch source: it keeps the techniques that make ATen fast (TensorIterator, vectorized kernels with runtime CPU dispatch, BLAS/MKL) without the breadth and indirection that make the original hard to read.

The goal is a codebase that someone curious about how PyTorch works inside can read end to end, while running at PyTorch speed on CPU.

Status: alpha. CPU only. Tensors with views and broadcasting, type promotion, elementwise ops, reductions, matmul, autograd, and an nn/optim package with enough to train MLPs. CNN layers and CUDA are next.

Install

pip install raxis

Wheels for Windows and Linux (x86-64), Python 3.10 to 3.14. raxis has no runtime dependencies; numpy is optional (.numpy(), raxis.from_numpy).

import raxis
from raxis import nn, optim

model = nn.Sequential(nn.Linear(784, 128), nn.ReLU(), nn.Linear(128, 10))
optimizer = optim.SGD(model.parameters(), lr=0.01, momentum=0.9)

x, y = raxis.randn((64, 784)), raxis.randint(0, 10, (64,))
loss = nn.functional.cross_entropy(model(x), y)
optimizer.zero_grad()
loss.backward()
optimizer.step()

The API follows PyTorch's, so most code only needs torch replaced by raxis.

Inside

Path What it holds
libraxis/raxis/tensor TensorImpl and storage, views and strides, type promotion, TensorIterator
libraxis/raxis/ops Operators and their CPU kernels, compiled once per ISA (AVX2, NEON, ...) and picked at runtime
libraxis/raxis/autograd Graph, engine and backward functions
libraxis/bindings pybind11 module raxis._C
raxis/ Python package: nn, optim, tensor printing

Code taken from PyTorch keeps a // From: aten/src/ATen/... comment pointing to the original.

Build from source

Requirements: a C++20 compiler (MSVC 17+, GCC 12+, Clang 14+), CMake 3.22+ and uv.

git clone --recursive https://github.com/pgmesa/raxis.git
cd raxis
uv sync --extra dev --extra cpu        # or --extra cu130 for CUDA PyTorch
uv run python scripts/build_libraxis.py
uv run pytest tests

uv sync installs the pinned build and test dependencies from uv.lock, including Intel MKL from PyPI and PyTorch, the reference the tests compare against. build_libraxis.py builds libraxis with CMake and installs it into the raxis/ package. To work on the C++ side, libraxis/CMakePresets.json has debug and release presets; CMakeLists.txt lists the build options (RAXIS_USE_*).

scripts/bench_ops.py benchmarks each op against PyTorch and NumPy, and examples/ has notebooks that train MLPs on two moons and MNIST with either raxis or PyTorch.

License

MIT. raxis includes code derived from PyTorch (BSD-3-Clause) and links SLEEF, mimalloc and Intel MKL: see THIRD_PARTY_NOTICES.txt.

Metadata

Release files for raxis 0.1.0

For a detailed explanation of source distributions (sdists) and built distributions (wheels), please see the package formats documentation.

Built distributions (wheels)

Table of built distributions (wheels) for raxis 0.1.0
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raxis-0.1.0-cp314-cp314-win_amd64.whl CPython 3.14 CPython 3.14 Windows x86-64 Details for raxis-0.1.0-cp314-cp314-win_amd64.whl
raxis-0.1.0-cp314-cp314-manylinux_2_27_x86_64.manylinux_2_28_x86_64.whl CPython 3.14 CPython 3.14 Linux glibc 2.27+ x86-64, Linux glibc 2.28+ x86-64 Details for raxis-0.1.0-cp314-cp314-manylinux_2_27_x86_64.manylinux_2_28_x86_64.whl
raxis-0.1.0-cp313-cp313-win_amd64.whl CPython 3.13 CPython 3.13 Windows x86-64 Details for raxis-0.1.0-cp313-cp313-win_amd64.whl
raxis-0.1.0-cp313-cp313-manylinux_2_27_x86_64.manylinux_2_28_x86_64.whl CPython 3.13 CPython 3.13 Linux glibc 2.28+ x86-64, Linux glibc 2.27+ x86-64 Details for raxis-0.1.0-cp313-cp313-manylinux_2_27_x86_64.manylinux_2_28_x86_64.whl
raxis-0.1.0-cp312-cp312-win_amd64.whl CPython 3.12 CPython 3.12 Windows x86-64 Details for raxis-0.1.0-cp312-cp312-win_amd64.whl
raxis-0.1.0-cp312-cp312-manylinux_2_27_x86_64.manylinux_2_28_x86_64.whl CPython 3.12 CPython 3.12 Linux glibc 2.27+ x86-64, Linux glibc 2.28+ x86-64 Details for raxis-0.1.0-cp312-cp312-manylinux_2_27_x86_64.manylinux_2_28_x86_64.whl
raxis-0.1.0-cp311-cp311-win_amd64.whl CPython 3.11 CPython 3.11 Windows x86-64 Details for raxis-0.1.0-cp311-cp311-win_amd64.whl
raxis-0.1.0-cp311-cp311-manylinux_2_27_x86_64.manylinux_2_28_x86_64.whl CPython 3.11 CPython 3.11 Linux glibc 2.28+ x86-64, Linux glibc 2.27+ x86-64 Details for raxis-0.1.0-cp311-cp311-manylinux_2_27_x86_64.manylinux_2_28_x86_64.whl
raxis-0.1.0-cp310-cp310-win_amd64.whl CPython 3.10 CPython 3.10 Windows x86-64 Details for raxis-0.1.0-cp310-cp310-win_amd64.whl
raxis-0.1.0-cp310-cp310-manylinux_2_27_x86_64.manylinux_2_28_x86_64.whl CPython 3.10 CPython 3.10 Linux glibc 2.27+ x86-64, Linux glibc 2.28+ x86-64 Details for raxis-0.1.0-cp310-cp310-manylinux_2_27_x86_64.manylinux_2_28_x86_64.whl

Total release size: 74.1 MB

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