Fragment of Bayesian networks¶

This class proposes a shallow copy of a part of Bayesian network. It can be used as a Bayesian network for inference algorithms (for instance).

class pyAgrum.BayesNetFragment(bn)¶

BayesNetFragment represents a part of a Bayesian network (subset of nodes). By default, the arcs and the CPTs are the same as the BN but local CPTs can be build to express different local dependencies. All the non local CPTs are not copied. Therefore a BayesNetFragment is a light object.

BayesNetFragment(BayesNet bn) -> BayesNetFragment

Parameters:

bn (pyAgrum.BayesNet) – the bn refered by the fragment

Parameters: bn (IBayesNet) –

addArcs(listArcs)¶

add a list of arcs in te model.

Parameters: listArcs (List[Tuple[intstr,intstr]]) – the list of arcs

addStructureListener(whenNodeAdded=None, whenNodeDeleted=None, whenArcAdded=None, whenArcDeleted=None)¶

Add the listeners in parameters to the list of existing ones.

Parameters

whenNodeAdded (lambda expression) – a function for when a node is added
whenNodeDeleted (lambda expression) – a function for when a node is removed
whenArcAdded (lambda expression) – a function for when an arc is added
whenArcDeleted (lambda expression) – a function for when an arc is removed

addVariables(listFastVariables, default_nbr_mod=2)¶

Add a list of variable in the form of ‘fast’ syntax.

Parameters

listFastVariables (List[str]) – the list of variables in ‘fast’ syntax.
default_nbr_mod (int) – the number of modalities for the variable if not specified following fast syntax. Note that default_nbr_mod=1 is mandatory to create variables with only one modality (for utility for instance).

Returns

the list of created ids.

Return type

List[int]

ancestors(norid)¶

give the set of nodeid of ancestors of a node

Parameters: norid (str|int) – the name or the id of the node
Returns: the set of ids of the ancestors of node norid.
Return type: Set[int]

arcs()¶

Returns: The lisf of arcs in the IBayesNet
Return type: list

check()¶

Check if the BayesNet is consistent (variables, CPT, …)

Returns: list of found issues
Return type: List[str]

checkConsistency(*args)¶

If a variable is added to the fragment but not its parents, there is no CPT consistant for this variable. This function checks the consistency for a variable of for all.

Parameters

n (int, str (optional)) – the id or the name of the variable. If no argument, the function checks all the variables.

Returns

True if the variable(s) is consistant.

Return type

boolean

Raises

pyAgrum.NotFound –
if the node is not found. –

children(norid)¶

Parameters

id (int) – the id of the parent
norid (object) –

Returns

the set of all the children

Return type

Set

completeInstantiation()¶

Give an instantiation over all the variables of the model

Returns: a complete Instantiation for the model
Return type: pyAgrum.Instantiation

connectedComponents()¶

connected components from a graph/BN

Compute the connected components of a pyAgrum’s graph or Bayesian Network (more generally an object that has nodes, children/parents or neighbours methods)

The firstly visited node for each component is called a ‘root’ and is used as a key for the component. This root has been arbitrarily chosen during the algorithm.

Returns: dict of connected components (as set of nodeIds (int)) with a nodeId (root) of each component as key.
Return type: dict(int,Set[int])

cpt(*args)¶

Returns the CPT of a variable.

Parameters

VarId (int) – A variable’s id in the pyAgrum.IBayesNet.
name (str) – A variable’s name in the pyAgrum.IBayesNet.

Returns

The variable’s CPT.

Return type

pyAgrum.Potential

Raises

pyAgrum.NotFound – If no variable’s id matches varId.

dag()¶

Returns: a constant reference to the dag of this BayesNet.
Return type: pyAgrum.DAG

descendants(norid)¶

give the set of nodeid of descendants of a node

Parameters: norid (str|int) – the name or the id of the node
Returns: the set of ids of the descendants of node norid.
Return type: Set[int]

dim()¶

Returns the dimension (the number of free parameters) in this BayesNet.

Returns: the dimension of the BayesNet
Return type: int

empty()¶

Check if there are some variables in the model.

Returns: True if there is no variable in the model.
Return type: bool

exists(node)¶

Check if a node with this name or id exists

Parameters

norid (str|int) – name or id of the searched node
node (int) –

Returns

True if there is a node with such a name or id

Return type

bool

existsArc(*args)¶

Check if an arc exists

Parameters

tail (str|int) – the name or id of the tail of the arc
head (str|int) – the name or the id of the head of the arc

Returns

True if tail->head is an arc.

Return type

bool

family(norid)¶

give the set of parents of a node and the node

Parameters: norid (str|int) – the node
Returns: the set of nodeId of the family of the node norid
Return type: Set[int]

hasSameStructure(other)¶

Parameters: pyAgrum.DAGmodel – a direct acyclic model
Returns: True if all the named node are the same and all the named arcs are the same
Return type: bool

idFromName(name)¶

Returns a variable’s id given its name in the graph.

Parameters: name (str) – The variable’s name from which the id is returned.
Returns: The variable’s node id.
Return type: int
Raises: pyAgrum.NotFound – If name does not match a variable in the graph

ids(names)¶

List of ids for a list of names of variables in the model

Parameters

lov (List[str]) – List of variable names
names (List[str]) –

Returns

The ids for the list of names of the graph variables

Return type

List[int]

installAscendants(*args)¶

Add the variable and all its ascendants in the fragment. No inconsistant node are created.

Parameters

n (int, str) – the id or the name of the variable.

Raises

pyAgrum.NotFound –
if the node is not found. –

Return type

None

installCPT(*args)¶

Install a local CPT for a node. Doing so, it changes the parents of the node in the fragment.

Parameters

n (int, str) – the id or the name of the variable.
pot (Potential) – the Potential to install

Raises

pyAgrum.NotFound – if the node is not found.

Return type

None

installMarginal(*args)¶

Install a local marginal for a node. Doing so, it removes the parents of the node in the fragment.

Parameters

n (int, str) – the id or the name of the variable.
pot (Potential) – the Potential (marginal) to install

Raises

pyAgrum.NotFound – if the node is not found.

Return type

None

installNode(*args)¶

Add a node to the fragment. The arcs that can be added between installed nodes are created. No specific CPT are created. Then either the parents of the node are already in the fragment and the node is consistant, or the parents are not in the fragment and the node is not consistant.

Parameters: n (int, str) – the id or the name of the variable.
Raises: pyAgrum.NotFound – if the node is not found.
Return type: None

isIndependent(*args)¶

check if nodes X and nodes Y are independent given nodes Z

Parameters

X (str|intList[str|int]) – a list of of nodeIds or names
Y (str|intList[str|int]) – a list of of nodeIds or names
Z (str|intList[str|int]) – a list of of nodeIds or names

Raises

InvalidArgument – if X and Y share variables

Returns

True if X and Y are independent given Z in the model

Return type

bool

isInstalledNode(*args)¶

Check if a node is in the fragment

Parameters: n (int, str) – the id or the name of the variable.
Return type: bool

jointProbability(i)¶

Parameters: i (pyAgrum.instantiation) – an instantiation of the variables
Returns: a parameter of the joint probability for the BayesNet
Return type: float

Warning

a variable not present in the instantiation is assumed to be instantiated to 0

log10DomainSize()¶

returns the log10 of the domain size of the model defined as the product of the domain sizes of the variables in the model.

Returns: the log10 domain size.
Return type: float

log2JointProbability(i)¶

Parameters: i (pyAgrum.instantiation) – an instantiation of the variables
Returns: a parameter of the log joint probability for the BayesNet
Return type: float

Warning

a variable not present in the instantiation is assumed to be instantiated to 0

maxNonOneParam()¶

Returns: The biggest value (not equal to 1) in the CPTs of the BayesNet
Return type: float

maxParam()¶

Returns: the biggest value in the CPTs of the BayesNet
Return type: float

maxVarDomainSize()¶

Returns: the biggest domain size among the variables of the BayesNet
Return type: int

minNonZeroParam()¶

Returns: the smallest value (not equal to 0) in the CPTs of the IBayesNet
Return type: float

minParam()¶

Returns: the smallest value in the CPTs of the IBayesNet
Return type: float

minimalCondSet(*args)¶

Returns, given one or many targets and a list of variables, the minimal set of those needed to calculate the target/targets.

Parameters

target (int) – The id of the target
targets (List[int]) – The ids of the targets
list (List[int]) – The list of available variables

Returns

The minimal set of variables

Return type

Set[int]

moralGraph()¶

Returns the moral graph of the BayesNet, formed by adding edges between all pairs of nodes that have a common child, and then making all edges in the graph undirected.

Returns: The moral graph
Return type: pyAgrum.UndiGraph

moralizedAncestralGraph(nodes)¶

build a UndiGraph by moralizing the Ancestral Graph of a list of nodes

Parameters: nodes (str|intList[str|int]) – the list of of nodeIds or names

Warning

gum.UndiGraph only knows NodeId. Hence the moralized ancestral graph does not include the names of the variables.graph

Returns: the moralized ancestral graph of the nodes
Return type: gum.UndiGraph

names()¶

Set of names of variables in the model

Returns: The names of the graph variables
Return type: Set[str]

nodeId(var)¶

Parameters: var (pyAgrum.DiscreteVariable) – a variable
Returns: the id of the variable
Return type: int
Raises: pyAgrum.IndexError – If the graph does not contain the variable

nodes()¶

Returns: the set of ids
Return type: Set[int]

nodeset(names)¶

Set of ids for a list of names of variables in the model

Parameters

lov (List[str]) – List of variable names
names (List[str]) –

Returns

The set of ids for the list of names of the graph variables

Return type

Set[int]

parents(norid)¶

Parameters

id – The id of the child node
norid (object) –

Returns

the set of the parents ids.

Return type

Set

property(name)¶

Returns the value associated to this property.

Properties are a way to keep some (name,value) together with de model.

Parameters: name (str) – the name of the property
Raises: NotFound – if no name property is found
Returns: The value associated to this name
Return type: str

propertyWithDefault(name, byDefault)¶

Returns the value associated to this property or the default value if there is no such property.

Properties are a way to keep some information (name,value) together with de model.

Parameters

name (str) – the name of the property
byDefault (str) – the value by default if no property has been found.

Returns

The value associated to this name or the value by default.

Return type

str

setProperty(name, value)¶

Create or change the couple (name,value) in the properties.

Properties are a way to keep some information (name,value) together with de model.

Parameters

name (str) – the name of the property
value (str) – the value of the property.

Return type

None

size()¶

Returns: the number of nodes in the graph
Return type: int

sizeArcs()¶

Returns: the number of arcs in the graph
Return type: int

toBN()¶

Create a BayesNet from a fragment.

Raises: pyAgrum.OperationNotAllowed – if the fragment is not consistent.
Return type: BayesNet

toDot()¶

Returns: a friendly display of the graph in DOT format
Return type: str

topologicalOrder()¶

Returns: the list of the nodes Ids in a topological order
Return type: List
Raises: pyAgrum.InvalidDirectedCycle – If this graph contains cycles

uninstallCPT(*args)¶

Remove a local CPT. The fragment can become inconsistant.

Parameters: n (int, str) – the id or the name of the variable.
Raises: pyAgrum.NotFound – if the node is not found.
Return type: None

uninstallNode(*args)¶

Remove a node from the fragment. The fragment can become inconsistant.

Parameters: n (int, str) – the id or the name of the variable.
Raises: pyAgrum.NotFound – if the node is not found.
Return type: None

variable(*args)¶

Parameters

id (int) – a variable’s id
name (str) – a variable’s name

Returns

the variable

Return type

pyAgrum.DiscreteVariable

Raises

pyAgrum.IndexError – If the graph does not contain the variable

variableFromName(name)¶

Parameters: name (str) – a variable’s name
Returns: the variable
Return type: pyAgrum.DiscreteVariable
Raises: pyAgrum.IndexError – If the graph does not contain the variable

variableNodeMap()¶

Returns: the variable node map
Return type: pyAgrum.variableNodeMap

whenArcAdded(src, _from, to)¶

Parameters

src (object) –
_from (int) –
to (int) –

Return type

None

whenArcDeleted(src, _from, to)¶

Parameters

src (object) –
_from (int) –
to (int) –

Return type

None

whenNodeAdded(src, id)¶

Parameters

src (object) –
id (int) –

Return type

None

whenNodeDeleted(src, id)¶

Parameters

src (object) –
id (int) –

Return type

None