Belief Propagation

class pgmpy.inference.ExactInference.BeliefPropagation(model)

Class for performing inference using Belief Propagation method.

Creates a Junction Tree or Clique Tree (JunctionTree class) for the input probabilistic graphical model and performs calibration of the junction tree so formed using belief propagation.

Parameters:

model (BayesianNetwork, MarkovNetwork, FactorGraph, JunctionTree) – model for which inference is to performed

calibrate()

Calibration using belief propagation in junction tree or clique tree.

Examples

>>> from pgmpy.models import BayesianNetwork
>>> from pgmpy.factors.discrete import TabularCPD
>>> from pgmpy.inference import BeliefPropagation
>>> G = BayesianNetwork([('diff', 'grade'), ('intel', 'grade'),
...                    ('intel', 'SAT'), ('grade', 'letter')])
>>> diff_cpd = TabularCPD('diff', 2, [[0.2], [0.8]])
>>> intel_cpd = TabularCPD('intel', 3, [[0.5], [0.3], [0.2]])
>>> grade_cpd = TabularCPD('grade', 3,
...                        [[0.1, 0.1, 0.1, 0.1, 0.1, 0.1],
...                         [0.1, 0.1, 0.1, 0.1, 0.1, 0.1],
...                         [0.8, 0.8, 0.8, 0.8, 0.8, 0.8]],
...                        evidence=['diff', 'intel'],
...                        evidence_card=[2, 3])
>>> sat_cpd = TabularCPD('SAT', 2,
...                      [[0.1, 0.2, 0.7],
...                       [0.9, 0.8, 0.3]],
...                      evidence=['intel'], evidence_card=[3])
>>> letter_cpd = TabularCPD('letter', 2,
...                         [[0.1, 0.4, 0.8],
...                          [0.9, 0.6, 0.2]],
...                         evidence=['grade'], evidence_card=[3])
>>> G.add_cpds(diff_cpd, intel_cpd, grade_cpd, sat_cpd, letter_cpd)
>>> bp = BeliefPropagation(G)
>>> bp.calibrate()

get_clique_beliefs()

Returns clique beliefs. Should be called after the clique tree (or junction tree) is calibrated.

get_cliques()

Returns cliques used for belief propagation.

get_sepset_beliefs()

Returns sepset beliefs. Should be called after clique tree (or junction tree) is calibrated.

map_query(variables=None, evidence=None, virtual_evidence=None, show_progress=True)

MAP Query method using belief propagation. Returns the highest probable state in the joint distributon of variables.

Parameters:

• variables (list) – list of variables for which you want to compute the probability

• virtual_evidence (list (default:None)) – A list of pgmpy.factors.discrete.TabularCPD representing the virtual evidences.

• evidence (dict) – a dict key, value pair as {var: state_of_var_observed} None if no evidence

• show_progress (boolean) – If True, shows a progress bar.

Examples

>>> from pgmpy.factors.discrete import TabularCPD
>>> from pgmpy.models import BayesianNetwork
>>> from pgmpy.inference import BeliefPropagation
>>> bayesian_model = BayesianNetwork([('A', 'J'), ('R', 'J'), ('J', 'Q'),
...                                 ('J', 'L'), ('G', 'L')])
>>> cpd_a = TabularCPD('A', 2, [[0.2], [0.8]])
>>> cpd_r = TabularCPD('R', 2, [[0.4], [0.6]])
>>> cpd_j = TabularCPD('J', 2,
...                    [[0.9, 0.6, 0.7, 0.1],
...                     [0.1, 0.4, 0.3, 0.9]],
...                    ['R', 'A'], [2, 2])
>>> cpd_q = TabularCPD('Q', 2,
...                    [[0.9, 0.2],
...                     [0.1, 0.8]],
...                    ['J'], [2])
>>> cpd_l = TabularCPD('L', 2,
...                    [[0.9, 0.45, 0.8, 0.1],
...                     [0.1, 0.55, 0.2, 0.9]],
...                    ['G', 'J'], [2, 2])
>>> cpd_g = TabularCPD('G', 2, [[0.6], [0.4]])
>>> bayesian_model.add_cpds(cpd_a, cpd_r, cpd_j, cpd_q, cpd_l, cpd_g)
>>> belief_propagation = BeliefPropagation(bayesian_model)
>>> belief_propagation.map_query(variables=['J', 'Q'],
...                              evidence={'A': 0, 'R': 0, 'G': 0, 'L': 1})

max_calibrate()

Max-calibration of the junction tree using belief propagation.

Examples

>>> from pgmpy.models import BayesianNetwork
>>> from pgmpy.factors.discrete import TabularCPD
>>> from pgmpy.inference import BeliefPropagation
>>> G = BayesianNetwork([('diff', 'grade'), ('intel', 'grade'),
...                    ('intel', 'SAT'), ('grade', 'letter')])
>>> diff_cpd = TabularCPD('diff', 2, [[0.2], [0.8]])
>>> intel_cpd = TabularCPD('intel', 3, [[0.5], [0.3], [0.2]])
>>> grade_cpd = TabularCPD('grade', 3,
...                        [[0.1, 0.1, 0.1, 0.1, 0.1, 0.1],
...                         [0.1, 0.1, 0.1, 0.1, 0.1, 0.1],
...                         [0.8, 0.8, 0.8, 0.8, 0.8, 0.8]],
...                        evidence=['diff', 'intel'],
...                        evidence_card=[2, 3])
>>> sat_cpd = TabularCPD('SAT', 2,
...                      [[0.1, 0.2, 0.7],
...                       [0.9, 0.8, 0.3]],
...                      evidence=['intel'], evidence_card=[3])
>>> letter_cpd = TabularCPD('letter', 2,
...                         [[0.1, 0.4, 0.8],
...                          [0.9, 0.6, 0.2]],
...                         evidence=['grade'], evidence_card=[3])
>>> G.add_cpds(diff_cpd, intel_cpd, grade_cpd, sat_cpd, letter_cpd)
>>> bp = BeliefPropagation(G)
>>> bp.max_calibrate()

query(variables, evidence=None, virtual_evidence=None, joint=True, show_progress=True)

Query method using belief propagation.

Parameters:

• variables (list) – list of variables for which you want to compute the probability

• evidence (dict) – a dict key, value pair as {var: state_of_var_observed} None if no evidence

• virtual_evidence (list (default:None)) – A list of pgmpy.factors.discrete.TabularCPD representing the virtual evidences.

• joint (boolean) – If True, returns a Joint Distribution over variables. If False, returns a dict of distributions over each of the variables.

• show_progress (boolean) – If True shows a progress bar.

Examples

>>> from pgmpy.factors.discrete import TabularCPD
>>> from pgmpy.models import BayesianNetwork
>>> from pgmpy.inference import BeliefPropagation
>>> bayesian_model = BayesianNetwork([('A', 'J'), ('R', 'J'), ('J', 'Q'),
...                                 ('J', 'L'), ('G', 'L')])
>>> cpd_a = TabularCPD('A', 2, [[0.2], [0.8]])
>>> cpd_r = TabularCPD('R', 2, [[0.4], [0.6]])
>>> cpd_j = TabularCPD('J', 2,
...                    [[0.9, 0.6, 0.7, 0.1],
...                     [0.1, 0.4, 0.3, 0.9]],
...                    ['R', 'A'], [2, 2])
>>> cpd_q = TabularCPD('Q', 2,
...                    [[0.9, 0.2],
...                     [0.1, 0.8]],
...                    ['J'], [2])
>>> cpd_l = TabularCPD('L', 2,
...                    [[0.9, 0.45, 0.8, 0.1],
...                     [0.1, 0.55, 0.2, 0.9]],
...                    ['G', 'J'], [2, 2])
>>> cpd_g = TabularCPD('G', 2, [[0.6], [0.4]])
>>> bayesian_model.add_cpds(cpd_a, cpd_r, cpd_j, cpd_q, cpd_l, cpd_g)
>>> belief_propagation = BeliefPropagation(bayesian_model)
>>> belief_propagation.query(variables=['J', 'Q'],
...                          evidence={'A': 0, 'R': 0, 'G': 0, 'L': 1})