Source code for pgmpy.inference.EliminationOrder

from abc import abstractmethod
from itertools import combinations

import numpy as np

from pgmpy.models import BayesianModel


[docs]class BaseEliminationOrder: """ Base class for finding elimination orders. """ def __init__(self, model): """ Init method for the base class of Elimination Orders. Parameters ---------- model: BayesianModel instance The model on which we want to compute the elimination orders. """ if not isinstance(model, BayesianModel): raise ValueError("Model should be a BayesianModel instance") self.bayesian_model = model self.moralized_model = self.bayesian_model.moralize() @abstractmethod
[docs] def cost(self, node): """ The cost function to compute the cost of elimination of each node. This method is just a dummy and returns 0 for all the nodes. Actual cost functions are implemented in the classes inheriting BaseEliminationOrder. Parameters ---------- node: string, any hashable python object. The node whose cost is to be computed. """ return 0
[docs] def get_elimination_order(self, nodes=None): """ Returns the optimal elimination order based on the cost function. The node having the least cost is removed first. Parameters ---------- nodes: list, tuple, set (array-like) The variables which are to be eliminated. Examples -------- >>> import numpy as np >>> from pgmpy.models import BayesianModel >>> from pgmpy.factors.discrete import TabularCPD >>> from pgmpy.inference.EliminationOrder import MinFill >>> model = BayesianModel([('c', 'd'), ('d', 'g'), ('i', 'g'), ... ('i', 's'), ('s', 'j'), ('g', 'l'), ... ('l', 'j'), ('j', 'h'), ('g', 'h')]) >>> cpd_c = TabularCPD('c', 2, np.random.rand(2, 1)) >>> cpd_d = TabularCPD('d', 2, np.random.rand(2, 2), ... ['c'], [2]) >>> cpd_g = TabularCPD('g', 3, np.random.rand(3, 4), ... ['d', 'i'], [2, 2]) >>> cpd_i = TabularCPD('i', 2, np.random.rand(2, 1)) >>> cpd_s = TabularCPD('s', 2, np.random.rand(2, 2), ... ['i'], [2]) >>> cpd_j = TabularCPD('j', 2, np.random.rand(2, 4), ... ['l', 's'], [2, 2]) >>> cpd_l = TabularCPD('l', 2, np.random.rand(2, 3), ... ['g'], [3]) >>> cpd_h = TabularCPD('h', 2, np.random.rand(2, 6), ... ['g', 'j'], [3, 2]) >>> model.add_cpds(cpd_c, cpd_d, cpd_g, cpd_i, cpd_s, cpd_j, ... cpd_l, cpd_h) >>> WeightedMinFill(model).get_elimination_order(['c', 'd', 'g', 'l', 's']) ['c', 's', 'l', 'd', 'g'] >>> WeightedMinFill(model).get_elimination_order(['c', 'd', 'g', 'l', 's']) ['c', 's', 'l', 'd', 'g'] >>> WeightedMinFill(model).get_elimination_order(['c', 'd', 'g', 'l', 's']) ['c', 's', 'l', 'd', 'g'] """ if not nodes: nodes = self.bayesian_model.nodes() ordering = [] while nodes: scores = {node: self.cost(node) for node in nodes} min_score_node = min(scores, key=scores.get) ordering.append(min_score_node) nodes.remove(min_score_node) return ordering
[docs] def fill_in_edges(self, node): """ Return edges needed to be added to the graph if a node is removed. Parameters ---------- node: string (any hashable python object) Node to be removed from the graph. """ return combinations(self.bayesian_model.neighbors(node), 2)
class WeightedMinFill(BaseEliminationOrder): def cost(self, node): """ Cost function for WeightedMinFill. The cost of eliminating a node is the sum of weights of the edges that need to be added to the graph due to its elimination, where a weight of an edge is the product of the weights, domain cardinality, of its constituent vertices. """ edges = combinations(self.moralized_model.neighbors(node), 2) return sum([self.bayesian_model.get_cardinality(edge[0]) * self.bayesian_model.get_cardinality(edge[1]) for edge in edges]) class MinNeighbours(BaseEliminationOrder): def cost(self, node): """ The cost of a eliminating a node is the number of neighbors it has in the current graph. """ return len(self.moralized_model.neighbors(node)) class MinWeight(BaseEliminationOrder): def cost(self, node): """ The cost of a eliminating a node is the product of weights, domain cardinality, of its neighbors. """ return np.prod([self.bayesian_model.get_cardinality(neig_node) for neig_node in self.moralized_model.neighbors(node)]) class MinFill(BaseEliminationOrder): def cost(self, node): """ The cost of a eliminating a node is the number of edges that need to be added (fill in edges) to the graph due to its elimination """ return len(list(self.fill_in_edges(node)))