Source code for fraud_eagle.likelihood

#
# likelihood.py
#
# Copyright (c) 2016-2017 Junpei Kawamoto
#
# This file is part of rgmining-fraud-eagle.
#
# rgmining-fraud-eagle is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# rgmining-fraud-eagle is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
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# You should have received a copy of the GNU General Public License
# along with rgmining-fraud-eagle. If not, see <http://www.gnu.org/licenses/>.
#
# pylint: disable=too-many-branches
"""Define likelihood functions.

This module defines a likelihood of a pair of user and product.
See :meth:`psi` for the detailed definition of the likelihood.
"""
from __future__ import absolute_import
from fraud_eagle.constants import PLUS, MINUS, GOOD, BAD, HONEST, FRAUD


[docs]def psi(user, product, review, epsilon): """Likelihood of a pair of user and product. The likelihood is dependent on the review of the user gives the product. The review is one of {+, -}. We defined constant representing "+" and "-", thus the review is one of the {:data:`PLUS<fraud_eagle.constants.PLUS>`, :data:`MINUS<fraud_eagle.constants.MINUS>`}. On the other hand, epsilon is a given parameter. The likelihood :math:`\\psi_{ij}^{s}`, where :math:`i` and :math:`j` are indexes of user and produce, respectively, and :math:`s` is a review i.e. :math:`s \\in {+, -}`, is given as following tables. If the review is :data:`PLUS<fraud_eagle.constants.PLUS>`, .. csv-table:: :header: review: +, Product: Good, Product: Bad User: Honest, 1 - :math:`\\epsilon`, :math:`\\epsilon` User: Fraud, 2 :math:`\\epsilon`, 1 - 2 :math:`\\epsilon` If the review is :data:`MINUS<fraud_eagle.constants.MINUS>`, .. csv-table:: :header: review: -, Product: Good, Product: Bad User: Honest, :math:`\\epsilon`, 1 - :math:`\\epsilon` User: Fraud, 1 - 2 :math:`\\epsilon`, 2 :math:`\\epsilon` Args: user: user label which must be one of the { \ :data:`HONEST<fraud_eagle.constants.HONEST>`, \ :data:`FRAUD<fraud_eagle.constants.FRAUD>`}. product: product label which must be one of the \ {:data:`GOOD<fraud_eagle.constants.GOOD>`, \ :data:`BAD<fraud_eagle.constants.BAD>`}. review: review label which must be one of the \ {:data:`PLUS<fraud_eagle.constants.PLUS>`, \ :data:`MINUS<fraud_eagle.constants.MINUS>`}. epsilon: a float parameter in :math:`[0,1]`. Returns: Float value representing a likelihood of the given values. """ if review == PLUS: if user == HONEST: if product == GOOD: return 1 - epsilon elif product == BAD: return epsilon elif user == FRAUD: if product == GOOD: return 2 * epsilon elif product == BAD: return 1 - 2 * epsilon elif review == MINUS: if user == HONEST: if product == GOOD: return epsilon elif product == BAD: return 1 - epsilon elif user == FRAUD: if product == GOOD: return 1 - 2 * epsilon elif product == BAD: return 2 * epsilon raise ValueError("Given arguments are invalid.", user, product, review)