Source code for qiskit.aqua.components.uncertainty_models.multivariate_variational_distribution

# This code is part of Qiskit.
#
# (C) Copyright IBM 2019, 2021.
#
# 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.

"""The Multivariate Variational Distribution."""

from typing import Optional, List, Union
import numpy as np

from qiskit import QuantumRegister, ClassicalRegister, QuantumCircuit
from .multivariate_distribution import MultivariateDistribution

# pylint: disable=invalid-name


class MultivariateVariationalDistribution(MultivariateDistribution):
    """The Multivariate Variational Distribution."""

    def __init__(self,
                 num_qubits: Union[List[int], np.ndarray],
                 var_form: QuantumCircuit,
                 params: Union[List[float], np.ndarray],
                 low: Optional[Union[List[float], np.ndarray]] = None,
                 high: Optional[Union[List[float], np.ndarray]] = None) -> None:
        """
        Args:
            num_qubits: List with the number of qubits per dimension
            var_form: Variational form
            params: Parameters for variational form
            low: List with the lower bounds per dimension, set to 0 for each dimension if None
            high: List with the upper bounds per dimension, set to 1 for each dimension if None
        """
        if low is None:
            low = np.zeros(len(num_qubits))
        if high is None:
            high = np.ones(len(num_qubits))
        self._num_qubits = num_qubits
        self._var_form = var_form

        # fix the order of the parameters in the circuit
        self._var_form_params = sorted(self._var_form.parameters, key=lambda p: p.name)

        self.params = params
        probabilities = np.zeros(2 ** sum(num_qubits))
        super().__init__(num_qubits, probabilities, low, high)  # type: ignore
        self._var_form = var_form
        self.params = params

    @staticmethod
    def _replacement():
        return 'a parameterized qiskit.QuantumCircuit'

    def build(self, qc, q, q_ancillas=None, params=None):
        param_dict = dict(zip(self._var_form_params, self.params))
        circuit_var_form = self._var_form.assign_parameters(param_dict)
        qc.append(circuit_var_form.to_instruction(), q)

    def set_probabilities(self, quantum_instance):
        """Set Probabilities

        Args:
            quantum_instance (QuantumInstance): Quantum Instance
        """
        q_ = QuantumRegister(self._num_qubits, name='q')
        qc_ = QuantumCircuit(q_)
        param_dict = dict(zip(self._var_form_params, self.params))
        circuit_var_form = self._var_form.assign_parameters(param_dict)

        qc_.append(circuit_var_form.to_instruction(), qc_.qubits)

        if quantum_instance.is_statevector:
            pass
        else:
            c_ = ClassicalRegister(self._num_qubits, name='c')
            qc_.add_register(c_)
            qc_.measure(q_, c_)
        result = quantum_instance.execute(qc_)
        if quantum_instance.is_statevector:
            result = result.get_statevector(qc_)
            values = np.multiply(result, np.conj(result))
            values = list(values.real)
        else:
            result = result.get_counts(qc_)
            keys = list(result)
            values = list(result.values())
            values = [float(v) / np.sum(values) for v in values]
            values = [x for _, x in sorted(zip(keys, values))]

        probabilities = values
        self._probabilities = np.array(probabilities)