aGrUM  0.13.2
How to use the graph classes

The basic idea of the implementation of graphs in aGrUM is to leave it "as pure as possible". Hence graphs consist of integers (gum::NodeId) and binary relations between them (Edge, Arc).

# The Graph Hierarchy

Precisely a graph contains a compact representation of a set of gum::NodeId, and can contain a set of gum::Arc and a set of gum::Edge.

In aGrUM,

(as shown in the inheritance diagram for gum::MixedGraph, the class hierarchy for graphs in aGrUM uses multiple inheritance.)

This pattern of inheritance allows aGrUM to have a quite standardized API for all basic operations in graphs: manipulating and iterating over nodes, edges and arcs.

# IDs, iterators and properties

Such representation of graphs has two major drawbacks that aGrUM has to face:

• how to certify that all node ids are unique in a graph?
• how to iterate on nodes, arcs, edges in a graph ?
• how to put properties (name/position/integer/flag) on nodes, edges and arcs?

#### ID factory

For aGrUM, each node has (is) an id. IDs begin from 1 (id>0).

For the uniqueness of ids, addNode() in NodeGraphPart contains an internal idFactory which guarantees this property.

There are two ways to bypass the idFactory :

Good programmers should treat with respect the idFactory.

#### Iterators

gum::NodeSet, gum::EdgeSet and gum::ArcSet have their own iterators (see gum::NodeSetIterator etc.). However aGrUM gives specialized iterators for graphs. These iterators are herited from the different 3 graphs part and may be (or not) a typedef for set iterators. We encourage to use these iterators when iterating on a graph.

For a graph gr of type G (G is gum::DiGraph, gum::DAG, gum::UndiGraph or gum::MixedGraph, etc.) :

G gr;
// iterate on nodes
for(const auto node : gr.nodes()) {
... // node is a gum::NodeId
}
// iterate on edges (if possible)
for(const auto & edge : gr.edges()) {
... // edge is a const gum::Edge&
}
// iterate on arcs (if possible)
for(const auto & arc =gr.arcs()) {
... // arc is a const gum::Arc&
}

#### Properties

Properties are the way to put (dynamic) informations within nodes, edges and arcs. Properties are just HashTable in which keys are gum::NodeId, Edge or Arc. NodeProperty, ArcProperty and EdgeProperty are the names of these classes.

for ( auto nodeId : g.nodes()) {
is_id_odd.set( nodeId, nodeId % 2 == 0 );
}
std::cout<<is_id_odd<<std::cout<<std::endl;
for ( auto i : is_id_odd)
std::cout<<i.first()<<" : "<<i.second()<<std::endl;

Equivalently, you could have written :

bool is_it_odd(const gum::NodeId& i) {
return i%2==0;
}