# Source code for qiskit.algorithms.time_evolvers.classical_methods.scipy_imaginary_evolver

# This code is part of Qiskit.
#
#
# obtain a copy of this license in the LICENSE.txt file in the root directory
#
# Any modifications or derivative works of this code must retain this
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"""Classical Quantum Imaginary Time Evolution."""

from ..time_evolution_problem import TimeEvolutionProblem
from ..time_evolution_result import TimeEvolutionResult
from ..imaginary_time_evolver import ImaginaryTimeEvolver
from .evolve import _evolve

[docs]class SciPyImaginaryEvolver(ImaginaryTimeEvolver):
r"""Classical Evolver for imaginary time evolution.

Evolves an initial state :math:|\Psi\rangle for an imaginary time :math:\tau = it
under a Hamiltonian :math:H, as provided in the evolution_problem.
Note that the precision of the evolver does not depend on the number of
timesteps taken.
"""

def __init__(self, num_timesteps: int):
r"""
Args:
num_timesteps: The number of timesteps in the simulation.
Raises:
ValueError: If num_timesteps is not a positive integer.
"""
self.num_timesteps = num_timesteps

[docs]    def evolve(self, evolution_problem: TimeEvolutionProblem) -> TimeEvolutionResult:
r"""Perform imaginary time evolution :math:\exp(-\tau H)|\Psi\rangle.

Evolves an initial state :math:|\Psi\rangle for an imaginary time :math:\tau
under a Hamiltonian :math:H, as provided in the evolution_problem.

Args:
evolution_problem: The definition of the evolution problem.

Returns:
Evolution result which includes an evolved quantum state.
"""
return _evolve(evolution_problem, self.num_timesteps, real_time=False)