Source code for qiskit_nature.second_q.formats.watson.watson_hamiltonian

# This code is part of a Qiskit project.
# (C) Copyright IBM 2022, 2023.
# This code is licensed under the Apache License, Version 2.0. You may
# obtain a copy of this license in the LICENSE.txt file in the root directory
# of this source tree or at
# Any modifications or derivative works of this code must retain this
# copyright notice, and modified files need to carry a notice indicating
# that they have been altered from the originals.

"""The Watson Hamiltonian."""

from __future__ import annotations

from dataclasses import dataclass
from typing import Generator

import numpy as np

import qiskit_nature.optionals as _optionals

if _optionals.HAS_SPARSE:
    # pylint: disable=import-error
    from sparse import SparseArray, as_coo

    class SparseArray:  # type: ignore
        """Empty SparseArray class
        Replacement if sparse.SparseArray is not present.


    def as_coo(*args):
        """Empty as_coo function
        Replacement if sparse.as_coo is not present.
        del args

[docs]@dataclass class WatsonHamiltonian: r"""A dataclass for the force and kinetic coefficients describing a Watson Hamiltonian. .. math:: \mathcal{H}_{vib}(Q_1, \ldots, Q_L) = - \frac{1}{2} \sum_{l=1}^L \frac{\partial^2}{\partial Q_l^2} + V(Q_1, \ldots, Q_L) """ quadratic_force_constants: SparseArray | np.ndarray """The quadratic-order force constants.""" cubic_force_constants: SparseArray | np.ndarray """The cubic-order force constants.""" quartic_force_constants: SparseArray | np.ndarray """The quartic-order force constants.""" kinetic_coefficients: SparseArray | np.ndarray """The kinetic coefficients.""" @staticmethod def _iter_array( array: SparseArray | np.ndarray, *, kinetic: bool = False, ) -> Generator[tuple[complex, tuple[int, ...]], None, None]: if isinstance(array, np.ndarray): for index in np.ndindex(*array.shape): value = array[index] if value: yield value, tuple((-1) ** kinetic * (i + 1) for i in index) elif isinstance(array, SparseArray): coo = as_coo(array) for value, *idx in zip(, *coo.coords): yield value, tuple((-1) ** kinetic * (i + 1) for i in idx) def __iter__(self) -> Generator[tuple[complex, tuple[int, ...]], None, None]: for value, index in self._iter_array(self.quadratic_force_constants): yield value, index for value, index in self._iter_array(self.cubic_force_constants): yield value, index for value, index in self._iter_array(self.quartic_force_constants): yield value, index for value, index in self._iter_array(self.kinetic_coefficients, kinetic=True): yield value, index