Junction Tree

class pgmpy.models.JunctionTree.JunctionTree(ebunch=None)

Class for representing Junction Tree.

Junction tree is undirected graph where each node represents a clique (list, tuple or set of nodes) and edges represent sepset between two cliques. Each sepset in G separates the variables strictly on one side of edge to other.

Parameters:

data (input graph) – Data to initialize graph. If data=None (default) an empty graph is created. The data is an edge list.

Examples

Create an empty JunctionTree with no nodes and no edges

>>> from pgmpy.models import JunctionTree
>>> G = JunctionTree()

G can be grown by adding clique nodes.

Nodes:

Add a tuple (or list or set) of nodes as single clique node.

>>> G.add_node(('a', 'b', 'c'))
>>> G.add_nodes_from([('a', 'b'), ('a', 'b', 'c')])

Edges:

G can also be grown by adding edges.

>>> G.add_edge(('a', 'b', 'c'), ('a', 'b'))

or a list of edges

>>> G.add_edges_from([(('a', 'b', 'c'), ('a', 'b')),
...                   (('a', 'b', 'c'), ('a', 'c'))])

add_edge(u, v, **kwargs)

Add an edge between two clique nodes.

Parameters:

• u (nodes) – Nodes can be any list or set or tuple of nodes forming a clique.

• v (nodes) – Nodes can be any list or set or tuple of nodes forming a clique.

Examples

>>> from pgmpy.models import JunctionTree
>>> G = JunctionTree()
>>> G.add_nodes_from([('a', 'b', 'c'), ('a', 'b'), ('a', 'c')])
>>> G.add_edges_from([(('a', 'b', 'c'), ('a', 'b')),
...                   (('a', 'b', 'c'), ('a', 'c'))])

check_model()

Check the model for various errors. This method checks for the following errors. In the same time also updates the cardinalities of all the random variables.

• Checks if clique potentials are defined for all the cliques or not.

• Check for running intersection property is not done explicitly over here as it done in the add_edges method.

Returns:

check – True if all the checks are passed

Return type:

boolean

copy()

Returns a copy of JunctionTree.

Returns:

JunctionTree

Return type:

copy of JunctionTree

Examples

>>> import numpy as np
>>> from pgmpy.factors.discrete import DiscreteFactor
>>> from pgmpy.models import JunctionTree
>>> G = JunctionTree()
>>> G.add_edges_from([(('a', 'b', 'c'), ('a', 'b')), (('a', 'b', 'c'), ('a', 'c'))])
>>> phi1 = DiscreteFactor(['a', 'b'], [1, 2], np.random.rand(2))
>>> phi2 = DiscreteFactor(['a', 'c'], [1, 2], np.random.rand(2))
>>> G.add_factors(phi1,phi2)
>>> modelCopy = G.copy()
>>> modelCopy.edges()
EdgeView([(('a', 'b'), ('a', 'b', 'c')), (('a', 'c'), ('a', 'b', 'c'))])
>>> G.factors
[<DiscreteFactor representing phi(a:1, b:2) at 0xb720ee4c>,
 <DiscreteFactor representing phi(a:1, c:2) at 0xb4e1e06c>]
>>> modelCopy.factors
[<DiscreteFactor representing phi(a:1, b:2) at 0xb4bd11ec>,
 <DiscreteFactor representing phi(a:1, c:2) at 0xb4bd138c>]

property states

Returns a dictionary mapping each node to its list of possible states.

Returns:

state_dict – Dictionary of nodes to possible states

Return type:

dict