Module operators 

Graph operators: unions, intersections, complements, subgraphs, simplification, rewiring and graph products (igraph_operators.h).

This module turns the operators of igraph’s Graph Operators chapter into methods of Graph. Operators that build a new graph borrow their operands (&self) and return a fresh Graph; operators that igraph performs in place take &mut self (simplify, contract_vertices, connect_neighborhood, reverse_edges, rewire). Clone the graph first if you need to keep the original.

Operators working on many graphs at once (e.g. Graph::union_many) are associated functions accepting any iterator of graph references, such as [&g1, &g2, &g3] or graphs.iter().

As in igraph, vertex ids are never “matched by name”: two graphs are combined by identifying vertices with the same id. Unless stated otherwise, the operands must have the same directedness, and graph, vertex and edge attributes are not handled by these wrappers.

Example

use igraph::prelude::*;

// A 4-cycle and a "diagonal" graph on the same vertex set.
let square = Graph::ring(4, false, false, true).unwrap();
let diagonals = Graph::from_edges(&[(0, 2), (1, 3)], 4, false).unwrap();

// Their union is K4, the complement of the square is the diagonals.
let k4 = square.union(&diagonals).unwrap();
assert_eq!(k4, Graph::full(4, false, false).unwrap());
assert_eq!(square.complementer(false).unwrap(), diagonals);
assert_eq!(k4.difference(&square).unwrap(), diagonals);

// Two disjoint copies of the square, then the subgraph induced by one of them.
let two = square.disjoint_union(&square).unwrap();
assert_eq!((two.vcount(), two.ecount()), (8, 8));
let back = two.induced_subgraph(4..8, SubgraphImplementation::Auto).unwrap();
assert_eq!(back, square);

// The Cartesian product of two edges is a square (up to relabeling).
let edge = Graph::full(2, false, false).unwrap();
let prod = edge.product(&edge, Product::Cartesian).unwrap();
assert!(prod.isomorphic(&square).unwrap());

Provided functionality

Rust	C function	What it does
Graph::disjoint_union	igraph_disjoint_union	side-by-side copy of two graphs
Graph::disjoint_union_many	igraph_disjoint_union_many	side-by-side copy of many graphs
Graph::union, Graph::union_map	igraph_union	edges in either graph (+ edge maps)
Graph::union_many, Graph::union_many_map	igraph_union_many	edges in any graph (+ edge maps)
Graph::intersection, Graph::intersection_map	igraph_intersection	edges in both graphs (+ edge maps)
Graph::intersection_many, Graph::intersection_many_map	igraph_intersection_many	edges in all graphs (+ edge maps)
Graph::difference	igraph_difference	edges of the first graph missing from the second
Graph::join	igraph_join	disjoint union plus all edges between the two parts
Graph::complementer	igraph_complementer	complement graph
Graph::compose, Graph::compose_map	igraph_compose	composition of relations
Graph::contract_vertices	igraph_contract_vertices	merge groups of vertices (in place)
Graph::permute_vertices	igraph_permute_vertices	relabel vertices
Graph::connect_neighborhood	igraph_connect_neighborhood	connect vertices within k steps (in place)
Graph::graph_power	igraph_graph_power	the k-th power of a graph
Graph::rewire	igraph_rewire	degree-preserving random edge switches (in place)
Graph::simplify	igraph_simplify	remove multi-edges and/or loops (in place)
Graph::induced_subgraph	igraph_induced_subgraph	subgraph induced by a vertex set
Graph::induced_subgraph_map	igraph_induced_subgraph_map	same, with the vertex id maps
Graph::induced_subgraph_edges	igraph_induced_subgraph_edges	ids of the edges inside a vertex set
Graph::subgraph_from_edges	igraph_subgraph_from_edges	subgraph spanned by an edge set
Graph::reverse_edges	igraph_reverse_edges	flip the direction of some edges (in place)
Graph::product	igraph_product	Cartesian, lexicographic, strong, tensor, modular products
Graph::rooted_product	igraph_rooted_product	rooted product
Graph::mycielskian	igraph_mycielskian	iterated Mycielski construction

igraph_add_edge, also declared in this header, is wrapped by the core method Graph::add_edge.

See also

• Ready-made graphs to feed these operators: Graph::famous, Graph::full, Graph::ring, Graph::square_lattice, Graph::hypercube, Graph::wheel, Graph::mycielski_graph (constructors) and Graph::full_bipartite (bipartite).
• Comparing results: == compares labelled graphs (Graph::is_same_graph); Graph::isomorphic and Graph::canonical_permutation (isomorphism) compare structure up to relabeling.
• Other ways to cut a graph apart: Graph::delete_vertices (core), Graph::decompose and Graph::neighborhood_graphs (components).
• Other randomizations: Graph::rewire_edges and Graph::degree_sequence_game (games).
• Changing directedness rather than edges: Graph::to_directed and Graph::to_undirected (conversion).

Structs

EdgeMapped

A graph produced by a binary operator, together with the edge maps that relate its edges to the edges of the two operands.

EdgeMappedMany

A graph produced by an operator on many graphs, together with one edge map per operand (see Graph::union_many_map and Graph::intersection_many_map).

InducedSubgraph

An induced subgraph together with the correspondence between its vertices and the vertices of the original graph (see Graph::induced_subgraph_map).

RewiringStats

Statistics of a Graph::rewire run (igraph_rewiring_stats_t).