Calculate the ground states of a 2d quantum Ising model using threading

Calculate the ground states of a 2d quantum Ising model using threading to parallelize within one machine.

# pylint: disable=invalid-name

import numpy as np

import qtealeaves as qtl
from qtealeaves.models import get_quantum_ising_2d


def main(tn_type=5, input_folder=None, output_folder=None):
    """
    Main method for the ground state simulation of a
    quantum Ising model in 2D. This setup uses threading
    on the python side.

    **Arguments**

    tn_type : int, optional
        Choose 5 for python-TTN, 6 for python-MPS.
        Default to 5.

    input_folder : str | None, optional
        Input folder. Default to None.

    output_folder : str | None, optional
        Output folder. Default to None.
    """
    gfields = np.linspace(0, 2, 21)

    if input_folder is None:
        input_folder = lambda params: "QI2d/input_g%2.4f" % (params["g"])
    if output_folder is None:
        output_folder = lambda params: "QI2d/output_g%2.4f" % (params["g"])

    model, my_ops = get_quantum_ising_2d()

    my_conv = qtl.convergence_parameters.TNConvergenceParameters(
        max_iter=5, max_bond_dimension=16
    )
    my_obs = qtl.observables.TNObservables()

    simulation = qtl.QuantumGreenTeaSimulation(
        model,
        my_ops,
        my_conv,
        my_obs,
        tn_type=tn_type,
        folder_name_input=input_folder,
        folder_name_output=output_folder,
        has_log_file=True,
        store_checkpoints=False,
    )

    params = []
    for gfield in gfields:
        params.append(
            {
                "L": 8,
                # model parameters
                "J": 1.0,
                "g": gfield,
            }
        )

    simulation.run(params, delete_existing_folder=True, nthreads=8)

    for elem in params:
        results = simulation.get_static_obs(elem)
        print(
            "TTN ground state energy is %4.8f at field g=%2.4f"
            % (results["energy"], elem["g"])
        )

    print(f"\nExample `{__file__}` ran successfully; no asserts implemented.")

    return


if __name__ == "__main__":
    main()