# ![PECOS](images/pecos_logo.svg)

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**Performance Estimator of Codes On Surfaces (PECOS)** is a library/framework dedicated to the study, development, and
evaluation of quantum error-correction protocols. It also offers tools for the study and evaluation of hybrid
quantum/classical compute execution models.

Initially conceived and developed in 2014 to verify lattice-surgery procedures presented in
[arXiv:1407.5103](https://arxiv.org/abs/1407.5103) and released publicly in 2018, PECOS filled the gap in
the QEC/QC tools available at that time. Over the years, it has grown into a framework for studying general QECCs and
hybrid computation.

## Features

- Quantum Error-Correction Tools: Advanced tools for studying quantum error-correction protocols and error models.
- Hybrid Quantum/Classical Execution: Evaluate advanced hybrid compute models, including support for classical compute,
calls to Wasm VMs, conditional branching, and more.
- Fast Simulation: Leverages a fast stabilizer simulation algorithm.
- Multi-language extensions: Core functionalities implemented via Rust for performance and safety. Additional add-ons
and extension support in C/C++ via Cython.
- LLVM IR Support: Execute LLVM Intermediate Representation programs for hybrid quantum/classical computing. LLVM support is optional - PECOS can be built without LLVM by using `--no-default-features` when building the Rust crates. When LLVM is enabled (default), requires LLVM version 14.

## Getting Started

Explore the capabilities of PECOS by delving into the [documentation](https://quantum-pecos.readthedocs.io).

## Repository Structure

PECOS now consists of multiple interconnected components:

- `/python/`: Contains Python packages
  - `/python/quantum-pecos/`: Main Python package (imports as `pecos`)
  - `/python/pecos-rslib/`: Python package with Rust extensions that utilize the `pecos` crate
- `/crates/`: Contains Rust crates
  - `/crates/pecos/`: Main Rust crate that collects the functionality of the other crates into one library
  - `/crates/pecos-core/`: Core Rust functionalities
  - `/crates/pecos-qsims/`: A collection of quantum simulators
  - `/crates/pecos-qec/`: Rust code for analyzing and exploring quantum error correction (QEC)
  - `/crates/pecos-qasm/`: Implementation of QASM parsing and execution
  - `/crates/pecos-llvm-runtime/`: Implementation of LLVM IR execution for hybrid quantum-classical programs
  - `/crates/pecos-engines/`: Quantum and classical engines for simulations
  - `/crates/pecos/`: Main PECOS library (includes CLI with `cli` feature)
  - `/crates/pecos-build/`: Developer tools CLI (LLVM setup, dependency management)
  - `/crates/pecos-python/`: Rust code for Python extensions
  - `/crates/benchmarks/`: A collection of benchmarks to test the performance of the crates
- `/julia/`: Contains Julia packages (experimental)
  - `/julia/PECOS.jl/`: Main Julia package
  - `/julia/pecos-julia-ffi/`: Rust FFI library for Julia bindings

### Quantum Error Correction Decoders

PECOS includes LDPC (Low-Density Parity-Check) quantum error correction decoders as optional components. See [DECODERS.md](DECODERS.md) for detailed information about:
- LDPC decoder algorithms and variants
- How to build and use decoders
- Performance considerations
- Architecture and development guide

You may find most of these crates in crates.io if you wish to utilize only a part of PECOS, e.g., the simulators.

## Versioning

We follow semantic versioning principles. However, before version 1.0.0, the MAJOR.MINOR.BUG format sees the roles
of MAJOR and MINOR shifted down a step. This means potential breaking changes might occur between MINOR increments, such
as moving from versions 0.1.0 to 0.2.0.

All Python packages and all Rust crates will have the same version amongst their
respective languages; however, Python and Rust versioning will differ.

## Latest Development

Stay updated with the latest developments on the
[PECOS Development branch](https://quantum-pecos.readthedocs.io/en/development/).

## Installation

### Python Package

To install the main Python package for general usage:

```sh
pip install quantum-pecos
```

This will install both `quantum-pecos` and its dependency `pecos-rslib`.

For optional dependencies:

```sh
pip install quantum-pecos[all]
```

**NOTE:** The `quantum-pecos` package is imported like: `import pecos` and not `import quantum_pecos`.

**NOTE:** To install pre-releases (the latest development code) from pypi you may have to specify the version you are
interested like so (e.g., for version `0.6.0.dev5`):
```sh
pip install quantum-pecos==0.6.0.dev5
```

**NOTE:** Certain simulators have special requirements and are not installed by the command above. Installation instructions for
these are provided [here](#simulators-with-special-requirements).


### Rust Crates

To use PECOS in your Rust project, add the following to your `Cargo.toml`:

```toml
[dependencies]
pecos = "0.x.x"  # Replace with the latest version
```

#### Optional Dependencies

- **LLVM version 14**: Required for LLVM IR execution support (optional)

  PECOS provides an automated installer or you can install manually:

  ```sh
  # Quick setup with automated installer (recommended):
  cargo run -p pecos --features cli -- llvm install
  cargo build
  ```

  The installer automatically configures PECOS after installation.

  For detailed LLVM installation instructions for all platforms (macOS, Linux, Windows), see the [**Getting Started Guide**](docs/user-guide/getting-started.md#llvm-for-qis-support).

  For full development environment setup, see the [**Development Setup Guide**](docs/development/DEVELOPMENT.md).

  **Building without LLVM:** If you don't need LLVM IR support:
  ```sh
  cargo build --no-default-features
  ```

### Julia Package (Experimental)

PECOS also provides experimental Julia bindings. To use the Julia package from the development branch:

```julia
using Pkg
Pkg.add(url="https://github.com/PECOS-packages/PECOS#dev", subdir="julia/PECOS.jl")
```

Then you can use it:

```julia
using PECOS
println(pecos_version())  # Prints PECOS version
```

**Note**: The Julia package requires the Rust FFI library to be built. Currently, you need to build it locally:
1. Clone the repository
2. Build the FFI library: `cd julia/pecos-julia-ffi && cargo build --release`
3. Add the package locally: `Pkg.develop(path="julia/PECOS.jl")`

## Development Setup

If you are interested in editing or developing the code in this project, see this
[development documentation](docs/development/DEVELOPMENT.md) to get started.

## Simulators with special requirements

Certain simulators from `pecos.simulators` require external packages that are not installed by `pip install .[all]`.

### GPU-Accelerated Simulators (CuStateVec and MPS)

- **`CuStateVec`** and **`MPS`** require:
  - Linux machine with NVIDIA GPU (Compute Capability 7.0+)
  - CUDA Toolkit 13 or 12 (system-level installation)
  - Python packages: `cupy-cuda13x`, `cuquantum-python-cu13`, `pytket-cutensornet`

**Installation:** See the comprehensive [CUDA Setup Guide](docs/user-guide/cuda-setup.md) for detailed step-by-step instructions.

**Quick install** (after installing CUDA Toolkit):
```bash
uv pip install quantum-pecos[cuda]

# For development with CUDA support:
make build-cuda  # Build with CUDA
make devc        # Full dev cycle (clean + build-cuda + test)
make devcl       # Dev cycle + linting
```

**Note:** When using `uv` or `pip`, install CUDA Toolkit via system package manager (e.g., `sudo apt install cuda-toolkit-13`), then install Python packages. Conda environments may conflict with `uv`/`venv` workflows.

## Uninstall

To uninstall:

```sh
pip uninstall quantum-pecos
```

## Citing

For publications utilizing PECOS, kindly cite PECOS such as:

```bibtex
@misc{pecos,
 author={Ciar\'{a}n Ryan-Anderson},
 title={PECOS: Performance Estimator of Codes On Surfaces},
 publisher = {GitHub},
 journal = {GitHub repository},
 howpublished={\url{https://github.com/PECOS-packages/PECOS}},
 URL = {https://github.com/PECOS-packages/PECOS},
 year={2018}
}
```
And/or the PhD thesis PECOS was first described in:
```bibtex
@phdthesis{crathesis,
 author={Ciar\'{a}n Ryan-Anderson},
 school = {University of New Mexico},
 title={Quantum Algorithms, Architecture, and Error Correction},
 journal={arXiv:1812.04735},
 URL = {https://digitalrepository.unm.edu/phyc_etds/203},
 year={2018}
}
```

You can also use the [Zenodo DOI](https://zenodo.org/records/13700104), which would result in a bibtex like:
```bibtex
@software{pecos_[year],
  author       = {Ciar\'{a}n Ryan-Anderson},
  title        = {PECOS-packages/PECOS: [version]]},
  month        = [month],
  year         = [year],
  publisher    = {Zenodo},
  version      = {[version]]},
  doi          = {10.5281/zenodo.13700104},
  url          = {https://doi.org/10.5281/zenodo.13700104}
}
```


## License

This project is licensed under the Apache-2.0 License - see the [LICENSE](./LICENSE) and [NOTICE](NOTICE) files for
details.

## Supported by

[![Quantinuum](./images/Quantinuum_(word_trademark).svg)](https://www.quantinuum.com/)
