Code source de qiskit.algorithms.evolvers.evolution_problem

# This code is part of Qiskit.
#
# (C) Copyright IBM 2022.
#
# 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 http://www.apache.org/licenses/LICENSE-2.0.
#
# 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.

"""Evolution problem class."""

from __future__ import annotations

from qiskit import QuantumCircuit
from qiskit.circuit import Parameter
from qiskit.opflow import OperatorBase, StateFn
from qiskit.utils.deprecation import deprecate_func
from ..list_or_dict import ListOrDict


class EvolutionProblem:
    """Deprecated: Evolution problem class.

    The EvolutionProblem class has been superseded by the
    :class:`qiskit.algorithms.time_evolvers.TimeEvolutionProblem` class.
    This class will be deprecated in a future release and subsequently
    removed after that.

    This class is the input to time evolution algorithms and must contain information on the total
    evolution time, a quantum state to be evolved and under which Hamiltonian the state is evolved.
    """

    @deprecate_func(
        additional_msg=(
            "Instead, use the class ``qiskit.algorithms.time_evolvers.TimeEvolutionProblem``. "
            "See https://qisk.it/algo_migration for a migration guide."
        ),
        since="0.24.0",
    )
    def __init__(
        self,
        hamiltonian: OperatorBase,
        time: float,
        initial_state: StateFn | QuantumCircuit | None = None,
        aux_operators: ListOrDict[OperatorBase] | None = None,
        truncation_threshold: float = 1e-12,
        t_param: Parameter | None = None,
        param_value_dict: dict[Parameter, complex] | None = None,
    ):
        """
        Args:
            hamiltonian: The Hamiltonian under which to evolve the system.
            time: Total time of evolution.
            initial_state: The quantum state to be evolved for methods like Trotterization.
                For variational time evolutions, where the evolution happens in an ansatz,
                this argument is not required.
            aux_operators: Optional list of auxiliary operators to be evaluated with the
                evolved ``initial_state`` and their expectation values returned.
            truncation_threshold: Defines a threshold under which values can be assumed to be 0.
                Used when ``aux_operators`` is provided.
            t_param: Time parameter in case of a time-dependent Hamiltonian. This
                free parameter must be within the ``hamiltonian``.
            param_value_dict: Maps free parameters in the problem to values. Depending on the
                algorithm, it might refer to e.g. a Hamiltonian or an initial state.

        Raises:
            ValueError: If non-positive time of evolution is provided.
        """

        self.t_param = t_param
        self.param_value_dict = param_value_dict
        self.hamiltonian = hamiltonian
        self.time = time
        self.initial_state = initial_state
        self.aux_operators = aux_operators
        self.truncation_threshold = truncation_threshold

    @property
    def time(self) -> float:
        """Returns time."""
        return self._time

    @time.setter
    def time(self, time: float) -> None:
        """
        Sets time and validates it.

        Raises:
            ValueError: If time is not positive.
        """
        if time <= 0:
            raise ValueError(f"Evolution time must be > 0 but was {time}.")
        self._time = time

    def validate_params(self) -> None:
        """
        Checks if all parameters present in the Hamiltonian are also present in the dictionary
        that maps them to values.

        Raises:
            ValueError: If Hamiltonian parameters cannot be bound with data provided.
        """
        if isinstance(self.hamiltonian, OperatorBase):
            t_param_set = set()
            if self.t_param is not None:
                t_param_set.add(self.t_param)
            hamiltonian_dict_param_set: set[Parameter] = set()
            if self.param_value_dict is not None:
                hamiltonian_dict_param_set = hamiltonian_dict_param_set.union(
                    set(self.param_value_dict.keys())
                )
            params_set = t_param_set.union(hamiltonian_dict_param_set)
            hamiltonian_param_set = set(self.hamiltonian.parameters)

            if hamiltonian_param_set != params_set:
                raise ValueError(
                    f"Provided parameters {params_set} do not match Hamiltonian parameters "
                    f"{hamiltonian_param_set}."
                )