In this example I will try to create the Alarm Bayesian Network using pgmpy and do some simple queries on the network. This network is mentioned in Bayesian Artificial Intelligence - Section 2.5.1 (https://bayesian-intelligence.com/publications/bai/book/BAI_Chapter2.pdf)



In [9]:

    
#Importing Library
from pgmpy.models import BayesianModel
from pgmpy.inference import VariableElimination



In [10]:

    
#Defining network structure

alarm_model = BayesianModel([('Burglary', 'Alarm'), 
                              ('Earthquake', 'Alarm'),
                              ('Alarm', 'JohnCalls'),
                              ('Alarm', 'MaryCalls')])

#Defining the parameters using CPT
from pgmpy.factors.discrete import TabularCPD

cpd_burglary = TabularCPD(variable='Burglary', variable_card=2,
                      values=[[.999], [0.001]])
cpd_earthquake = TabularCPD(variable='Earthquake', variable_card=2,
                       values=[[0.998], [0.002]])
cpd_alarm = TabularCPD(variable='Alarm', variable_card=2,
                        values=[[0.999, 0.71, 0.06, 0.05],
                                [0.001, 0.29, 0.94, 0.95]],
                        evidence=['Burglary', 'Earthquake'],
                        evidence_card=[2, 2])
cpd_johncalls = TabularCPD(variable='JohnCalls', variable_card=2,
                      values=[[0.95, 0.1], [0.05, 0.9]],
                      evidence=['Alarm'], evidence_card=[2])
cpd_marycalls = TabularCPD(variable='MaryCalls', variable_card=2,
                      values=[[0.1, 0.7], [0.9, 0.3]],
                      evidence=['Alarm'], evidence_card=[2])

# Associating the parameters with the model structure
alarm_model.add_cpds(cpd_burglary, cpd_earthquake, cpd_alarm, cpd_johncalls, cpd_marycalls)



In [11]:

    
# Checking if the cpds are valid for the model
alarm_model.check_model()









    Out[11]:





True



In [12]:

    
# Viewing nodes of the model
alarm_model.nodes()









    Out[12]:





NodeView(('Burglary', 'Alarm', 'Earthquake', 'JohnCalls', 'MaryCalls'))



In [13]:

    
# Viewing edges of the model
alarm_model.edges()









    Out[13]:





OutEdgeView([('Burglary', 'Alarm'), ('Alarm', 'JohnCalls'), ('Alarm', 'MaryCalls'), ('Earthquake', 'Alarm')])



In [15]:

    
#Checking independcies of a node
alarm_model.local_independencies('Burglary')









    Out[15]:





(Burglary _|_ Earthquake)



In [16]:

    
#Listing all Independencies
alarm_model.get_independencies()









    Out[16]:





(Burglary _|_ Earthquake)
(Burglary _|_ MaryCalls, JohnCalls | Alarm)
(Burglary _|_ JohnCalls | MaryCalls, Alarm)
(Burglary _|_ MaryCalls, JohnCalls | Alarm, Earthquake)
(Burglary _|_ MaryCalls | JohnCalls, Alarm)
(Burglary _|_ JohnCalls | MaryCalls, Alarm, Earthquake)
(Burglary _|_ MaryCalls | Alarm, JohnCalls, Earthquake)
(Earthquake _|_ Burglary)
(Earthquake _|_ MaryCalls, JohnCalls | Alarm)
(Earthquake _|_ MaryCalls, JohnCalls | Burglary, Alarm)
(Earthquake _|_ JohnCalls | MaryCalls, Alarm)
(Earthquake _|_ MaryCalls | JohnCalls, Alarm)
(Earthquake _|_ JohnCalls | Burglary, MaryCalls, Alarm)
(Earthquake _|_ MaryCalls | Burglary, JohnCalls, Alarm)
(JohnCalls _|_ Burglary, MaryCalls, Earthquake | Alarm)
(JohnCalls _|_ MaryCalls, Earthquake | Burglary, Alarm)
(JohnCalls _|_ Burglary, Earthquake | MaryCalls, Alarm)
(JohnCalls _|_ Burglary, MaryCalls | Alarm, Earthquake)
(JohnCalls _|_ Earthquake | Burglary, MaryCalls, Alarm)
(JohnCalls _|_ MaryCalls | Burglary, Alarm, Earthquake)
(JohnCalls _|_ Burglary | MaryCalls, Alarm, Earthquake)
(MaryCalls _|_ Burglary, JohnCalls, Earthquake | Alarm)
(MaryCalls _|_ JohnCalls, Earthquake | Burglary, Alarm)
(MaryCalls _|_ Burglary, JohnCalls | Alarm, Earthquake)
(MaryCalls _|_ Burglary, Earthquake | JohnCalls, Alarm)
(MaryCalls _|_ JohnCalls | Burglary, Alarm, Earthquake)
(MaryCalls _|_ Earthquake | Burglary, JohnCalls, Alarm)
(MaryCalls _|_ Burglary | Alarm, JohnCalls, Earthquake)