magnetron 0.2.3

magnetron

A compact machine learning runtime for developers who want to understand, control, and optimize the full stack.
Native C core, modern Python API, no runtime dependencies, no bloat.

Documentation »

Qwen3 Inference Example · Autoencoder Training Example · GPT-2 Inference Example

About

Magnetron is a machine learning runtime built from scratch in C, with a small modern Python interface for usability.
It implements its own tensor system, operator set, autograd engine, and execution model - without relying on large external frameworks.

The goal is simple:

Keep the stack small enough to understand and be hackable, but powerful enough to run real models.

This makes Magnetron useful in two situations:

• when you want full control over execution and memory
• when you want a clean base for experimentation or new ideas

Why Magnetron?

Magnetron is not trying to compete with PyTorch on ecosystem or feature count.

Instead, it optimizes for a different axis:

If you want to:

• understand how your model actually runs
• experiment with kernels, memory layouts, or execution
• port ML workloads to unusual hardware

Magnetron gives you a much shorter path.

Architecture Overview

Magnetron is built as a single, cohesive runtime, not a collection of loosely coupled libraries.

• Tensor system
  Owns dtype, shape, strides, and memory – supports a full view system with a view solver, enabling complex slicing, reshaping, and broadcasting semantics similar to PyTorch while remaining explicit and predictable.

• Execution model
  Eager execution with a dynamic autograd graph (reverse-mode), constructed per forward pass and traversed during backward.

• Operator backend
  Central dispatch layer mapping high-level operations to architecture-specific kernel implementations.

• CPU backend
  Multi-dispatch design with compile-time optimized kernels for a wide range of microarchitectures (Intel, AMD Zen1–Zen5, ARM).
  At runtime, CPUID-based detection selects the most optimal kernel path automatically.
  Supports multiple SIMD ISAs and extensions, including SSE (1–4), AVX, AVX2, FMA, AVX-512, AVX-512-BF16, AVX-512-FP16, F16C and ARM NEON, combined with multithreaded execution.

• CUDA backend (in progress)
  Kernel layer is implemented - Memory management, execution pipeline, and integration are actively being completed.

• Serialization
  Native .mag format designed for zero-copy, memory-mapped loading, enabling fast startup and efficient large model handling.
  Conversion tools are provided to import weights from external formats.

• Backend extensibility
  The architecture is intentionally clean and modular, making it straightforward to introduce new backends or target additional hardware platforms.

The system is intentionally kept tight and explicit, so each layer is understandable, controllable, and replaceable without hidden complexity.

Highlights

• Practical, not just educational
  Capable of running modern LLM inference (e.g. Qwen3 in BF16), not just toy models.

• Small, controllable ML runtime
  Designed to stay inspectable end-to-end - no hidden execution layers or opaque backends.

• True ownership of execution
  You can reason about memory layout, kernel dispatch, and graph behavior without abstraction barriers.

• Hardware-aware by design
  Not a generic backend wrapper - kernels and execution are written with specific ISAs and microarchitectures in mind.

• Zero-copy model loading
  Memory-mapped .mag format enables fast startup and efficient handling of large models.

• Built for experimentation
  Easy to modify operators, add kernels, or prototype new execution strategies.

• Minimal runtime surface
  Native extension with no required Python dependencies - easy to deploy and embed.

Example Models

End-to-end demos live under examples/.

Operator Cheat Sheet

Magnetron provides a compact but expressive operator set covering:

• elementwise operations (add, mul, div, ...)
• reductions (sum, mean, ...)
• tensor transformations (view, reshape, permute, ...)
• neural building blocks (matmul, softmax, layernorm, ...)
• type casting and memory views

A full reference of operators, data types, and semantics is available here:

→ Magnetron Cheat Sheet

Installation

Magnetron is available on PyPI.

Make sure you are inside a Python virtual environment.

pip install magnetron

or with uv:

uv pip install magnetron

Local Development

Clone the repository and install locally:

git clone --recursive https://github.com/MarioSieg/magnetron
cd magnetron
uv pip install . -v

For C/C++ development, open the project root (containing CMakeLists.txt) in an IDE such as CLion.

Quick start

from magnetron import Tensor, nn, optim

x = Tensor([[0.0, 0.0], [0.0, 1.0], [1.0, 0.0], [1.0, 1.0]])
y = Tensor([[0.0], [1.0], [1.0], [0.0]])

model = nn.Sequential(nn.Linear(2, 2), nn.Tanh(), nn.Linear(2, 1), nn.Tanh())

optimizer = optim.SGD(model.parameters(), lr=1e-1)
criterion = nn.MSELoss()

for epoch in range(2000):
    y_hat = model(x)
    loss = criterion(y_hat, y)
    loss.backward()
    optimizer.step()
    optimizer.zero_grad()

    if epoch % 100 == 0:
        print(f'Epoch {epoch:4d} | Loss {loss.item():.6f}')

y_hat = model(x)
for i in range(x.shape[0]):
    print(f'Expected: {y[i].item():.1f}, Predicted: {y_hat[i].item():.4f}')

Roadmap

• 🚧 CUDA backend
  Finish memory model, execution pipeline, and stabilize for production use.

• 🚧 Multi-GPU execution
  Introduce scalable execution across multiple devices.

• 🚧 New CPU architectures
  Support for LoongArch and RISC-V.

• 🧪 JIT compilation
  Custom SSA-based IR with register allocation and target-specific instruction emission.

History

Magnetron started in 2024 as a personal project to understand how machine learning frameworks work internally: tensor storage, operator dispatch, autograd, and inference execution. What began as a learning project gradually evolved into a full runtime with its own tensor engine, native snapshot format, SIMD-specialized CPU backend, and support for running modern models such as Qwen3 in BF16. Today, Magnetron is developed both as a practical inference/runtime system and as a research platform for experimenting with new backends, execution strategies, and low-level ML systems ideas.

License

(c) 2026 Mario Sieg - mario.sieg.64@gmail.com
Distributed under the Apache 2 License.
Developed in Berlin, Germany.

Similar Projects

• PyTorch
• GGML
• tinygrad
• MLX