mdopt — Discrete Optimisation in the MPS-MPO Language

mdopt is a python package built on top of numpy for discrete optimisation in the tensor-network (specifically, MPS-MPO) language.

Installation

To install the current release, use the package manager pip.

pip install mdopt

Otherwise, clone the repository and use poetry.

poetry install

mdopt at a glance

import logging
import numpy as np
import qecstruct as qec
from mdopt.mps.utils import create_custom_product_state
from mdopt.optimiser.utils import (
    SWAP,
    XOR_BULK,
    XOR_LEFT,
    XOR_RIGHT,
)
from examples.decoding.decoding import (
    linear_code_constraint_sites,
    linear_code_prepare_message,
)
from examples.decoding.decoding import (
    apply_bitflip_bias,
    apply_constraints,
    decode_message,
)

logging.basicConfig(
    level=logging.INFO, format="%(asctime)s - %(levelname)s - %(message)s"
)

NUM_BITS = 24
CHI_MAX = 256
NUM_EXPERIMENTS = 10

SEED = 123
seed_seq = np.random.SeedSequence(SEED)

error_rates = np.linspace(0.1, 0.3, 10)
failures_statistics = {}

for ERROR_RATE in error_rates:
    logging.info(
        f"Starting experiments for NUM_BITS={NUM_BITS}, CHI_MAX={CHI_MAX}, ERROR_RATE={ERROR_RATE}"
    )
    failures = []

    for l in range(NUM_EXPERIMENTS):
        new_seed = seed_seq.spawn(1)[0]
        rng = np.random.default_rng(new_seed)
        random_integer = rng.integers(1, 10**8 + 1)
        SEED = random_integer

        CHECK_DEGREE, BIT_DEGREE = 4, 3
        NUM_CHECKS = int(BIT_DEGREE * NUM_BITS / CHECK_DEGREE)
        if NUM_BITS / NUM_CHECKS != CHECK_DEGREE / BIT_DEGREE:
            raise ValueError("The Tanner graph of the code must be bipartite.")
        PROB_BIAS = ERROR_RATE

        code = qec.random_regular_code(
            NUM_BITS, NUM_CHECKS, BIT_DEGREE, CHECK_DEGREE, qec.Rng(SEED)
        )
        code_constraint_sites = linear_code_constraint_sites(code)

        INITIAL_CODEWORD, PERTURBED_CODEWORD = linear_code_prepare_message(
            code, ERROR_RATE, error_model=qec.BinarySymmetricChannel, seed=SEED
        )
        tensors = [XOR_LEFT, XOR_BULK, SWAP, XOR_RIGHT]

        initial_codeword_state = create_custom_product_state(
            INITIAL_CODEWORD, form="Right-canonical"
        )
        perturbed_codeword_state = create_custom_product_state(
            PERTURBED_CODEWORD, form="Right-canonical"
        )

        logging.info("Applying bitflip bias to the perturbed codeword state.")
        perturbed_codeword_state = apply_bitflip_bias(
            mps=perturbed_codeword_state,
            sites_to_bias="All",
            prob_bias_list=PROB_BIAS,
            renormalise=True,
        )

        try:
            logging.info("Applying constraints to the perturbed codeword state.")
            perturbed_codeword_state = apply_constraints(
                perturbed_codeword_state,
                code_constraint_sites,
                tensors,
                chi_max=CHI_MAX,
                renormalise=True,
                result_to_explicit=False,
                strategy="Optimised",
                silent=False,
            )
            logging.info("Decoding the perturbed codeword state using DMRG.")
            dmrg_container, success = decode_message(
                message=perturbed_codeword_state,
                codeword=initial_codeword_state,
                chi_max_dmrg=CHI_MAX,
            )
            if success == 1:
                logging.info("Decoding successful.")
            else:
                logging.info("Decoding failed.")
        except Exception as e:
            logging.error(f"Failed in DMRG decoding: {str(e)}", exc_info=True)
            success = 0

        failures.append(1 - success)
        logging.info(
            f"Finished experiment {l} for NUM_BITS={NUM_BITS}, CHI_MAX={CHI_MAX}, ERROR_RATE={ERROR_RATE}"
        )

    failures_statistics[(NUM_BITS, CHI_MAX, ERROR_RATE)] = failures
    failures_key = (
        f"numbits{NUM_BITS}_bonddim{CHI_MAX}_errorrate{ERROR_RATE}"
    )
    logging.info(
        f"Completed experiments for {failures_key} with {np.mean(failures)*100:.2f}% failure rate."
    )

For more examples, see the mdopt examples folder.

Cite

If you happen to find mdopt useful in your research, please consider supporting development by citing it.

@software{mdopt2022,
  author = {Aleksandr Berezutskii},
  title = {mdopt: Discrete optimisation in the tensor-network (specifically, MPS-MPO) language.},
  url = {https://github.com/quicophy/mdopt},
  year = {2022},
}

Contribution guidelines

If you want to contribute to mdopt, be sure to follow GitHub's contribution guidelines. This project adheres to our code of conduct. By participating, you are expected to uphold this code.

We use GitHub issues for tracking requests and bugs, please direct specific questions to the maintainers.

The mdopt project strives to abide by generally accepted best practices in open-source software development, such as:

• apply the desired changes and resolve any code conflicts,
• run the tests and ensure they pass,
• build the package from source.