<< Click to Display Table of Contents >> Navigation:  Tutorials > Tutorial 2: Inference with a Bayesian Network > Tutorial2.py

import pysmile

 

# Tutorial2 loads the XDSL file created by Tutorial1,

# then performs the series of inference calls,

# changing evidence each time.

 

class Tutorial2:

    def __init__(self):

        print("Starting Tutorial2...")

        net = pysmile.Network()

        

        # load the network created by Tutorial1

        net.read_file("tutorial1.xdsl")

        

        print("Posteriors with no evidence set:")

        net.update_beliefs()

        self.print_all_posteriors(net)

        

        print("Setting Forecast=Good.")

        self.change_evidence_and_update(net, "Forecast", "Good")

        

        print("Adding Economy=Up.")

        self.change_evidence_and_update(net, "Economy", "Up")

        

        print("Changing Forecast to Poor, keeping Economy=Up.")

        self.change_evidence_and_update(net, "Forecast", "Poor")

        

        print("Removing evidence from Economy, keeping Forecast=Poor.")

        self.change_evidence_and_update(net, "Economy", None)

        

        print("Tutorial2 complete.")

 

 

    def print_posteriors(self, net, node_handle):

        node_id = net.get_node_id(node_handle)

        if net.is_evidence(node_handle):

            print(node_id + " has evidence set (" +

                  net.get_outcome_id(node_handle, 

                                     net.get_evidence(node_handle)) + ")")

        else :

            posteriors = net.get_node_value(node_handle)

            for i in range(0, len(posteriors)):

                print("P(" + node_id + "=" + 

                      net.get_outcome_id(node_handle, i) +

                      ")=" + str(posteriors[i]))

 

    def print_all_posteriors(self, net):

        for handle in net.get_all_nodes():

            self.print_posteriors(net, handle)

 

    

    def change_evidence_and_update(self, net, node_id, outcome_id):

        if outcome_id is not None:

            net.set_evidence(node_id, outcome_id)        

        else:

            net.clear_evidence(node_id)

        

        net.update_beliefs()

        self.print_all_posteriors(net)

        print("")