# -*- coding: utf-8 -*-
# This code is part of Qiskit.
#
# (C) Copyright IBM 2018, 2020.
#
# 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.
"""
This module contains the definition of data mapping function for feature map.
"""
import functools
import numpy as np
[docs]def self_product(x: np.ndarray) -> float:
"""
Define a function map from R^n to R.
Args:
x: data
Returns:
float: the mapped value
"""
coeff = x[0] if len(x) == 1 else \
functools.reduce(lambda m, n: m * n, np.pi - x)
return coeff