Module constructors 

Deterministic graph generators (igraph_constructors.h).

This module turns igraph’s deterministic constructors into associated functions of Graph returning Result<Graph>: given the same arguments they always build the very same graph, with the same vertex and edge ids. (Random generators live in crate::games.)

use igraph::prelude::*;

// The Petersen graph, three ways: by name, as G(5, 2), and from its LCF code.
let by_name = Graph::famous("Petersen").unwrap();
let gp = Graph::generalized_petersen(5, 2).unwrap();
assert_eq!((by_name.vcount(), by_name.ecount()), (10, 15));
assert_eq!((gp.vcount(), gp.ecount()), (10, 15));
// Both are 3-regular.
for g in [&by_name, &gp] {
    let degrees = g.degree(VertexSelector::All, NeighborMode::All, Loops::Twice).unwrap();
    assert!(degrees.iter().all(|&d| d == 3));
}

// A 3x4 grid, a 6-cycle and a star with 5 leaves.
let grid = Graph::square_lattice(&[3, 4], 1, false, false, None).unwrap();
assert_eq!((grid.vcount(), grid.ecount()), (12, 17));
let c6 = Graph::cycle_graph(6, false, false).unwrap();
assert_eq!(c6.ecount(), 6);
let star = Graph::star(6, StarMode::Undirected, 0).unwrap();
assert_eq!(star.degree_of(0, NeighborMode::All, Loops::Twice).unwrap(), 5);

Provided functionality

Family	Functions
From matrices	Graph::adjacency, Graph::weighted_adjacency, Graph::sparse_adjacency, Graph::sparse_weighted_adjacency
From edge lists	Graph::small (see also Graph::from_edges)
Paths, cycles, stars	Graph::ring, Graph::path_graph, Graph::cycle_graph, Graph::star, Graph::wheel
Complete graphs	Graph::full, Graph::full_citation, Graph::full_multipartite, Graph::turan
Lattices	Graph::square_lattice, Graph::triangular_lattice, Graph::hexagonal_lattice, Graph::hypercube
Trees	Graph::kary_tree, Graph::symmetric_tree, Graph::regular_tree, Graph::tree_from_parent_vector, Graph::from_prufer
Circulant-like	Graph::circulant, Graph::generalized_petersen, Graph::lcf, Graph::extended_chordal_ring
Word graphs	Graph::de_bruijn, Graph::kautz
Named graphs	Graph::famous (with FamousGraph), Graph::atlas, Graph::mycielski_graph
Degree sequences	Graph::realize_degree_sequence, Graph::realize_bipartite_degree_sequence
Derived graphs	Graph::linegraph

The corresponding chapter of the C documentation is Deterministic graph generators.

Conventions

• Vertex counts and sizes are usize; values that may legitimately be negative (shifts, parent ids, degrees coming from Graph::degree) are i64.
• Every function returns an Error rather than panicking on invalid input; most errors are ErrorKind::InvalidValue.

See also

Need	Where
Random graphs (Erdős–Rényi, random regular, random trees, degree sequences, …)	crate::games, e.g. Graph::erdos_renyi_game_gnm, Graph::k_regular_game, Graph::tree_game, Graph::degree_sequence_game
The inverse conversions (graph → matrix, tree → Prüfer code)	Graph::get_adjacency, Graph::get_adjacency_sparse, Graph::to_prufer in crate::conversion
Bipartite constructors	Graph::full_bipartite, BipartiteGraph in crate::bipartite
Graphs derived from other graphs	Graph::complementer, Graph::mycielskian, Graph::disjoint_union in crate::operators
Is a degree sequence realizable at all?	is_graphical, is_bigraphical
Comparing generated graphs up to relabelling	Graph::isomorphic, Graph::count_automorphisms in crate::isomorphism
Drawing them	Graph::layout_circle (rings), Graph::layout_star, Graph::layout_grid (lattices), Graph::layout_reingold_tilford (trees) in crate::layout
Reading graphs from files	crate::foreign

use igraph::prelude::*;

// LCF notation and the named graph agree up to relabelling: the Heawood
// graph two ways.
let heawood = Graph::famous("Heawood")?;
assert!(Graph::lcf(14, &[5, -5], 7)?.isomorphic(&heawood)?);
// Its automorphism group PGL(2, 7) has order 336, and its girth is 6.
assert_eq!(heawood.count_automorphisms(None)?, 336.0);
assert_eq!(heawood.girth()?, Some(6));

// Round trip through the adjacency matrix of the conversion module.
let a = heawood.get_adjacency(GetAdjacency::Both, None, Loops::Twice)?;
assert_eq!(Graph::adjacency(&a, Adjacency::Undirected, Loops::Twice)?, heawood);

Differences from the C library

A few defects of igraph 1.0.0 and 1.0.1 (the generator sources are unchanged in 1.0.1) are worked around on the Rust side, so the wrappers behave as documented:

• Graph::sparse_adjacency / Graph::sparse_weighted_adjacency agree with their dense counterparts even when an entry below the diagonal has no mirror entry (igraph drops it in the unweighted Max mode and in the weighted Max, Min and Plus modes), and when explicit zeros are given in the Undirected mode (igraph’s structural symmetry test would reject them).
• Graph::adjacency and Graph::sparse_adjacency reject NaN, infinite, negative and fractional edge counts (igraph casts them to integers unchecked).
• Graph::star and Graph::wheel with n = 1 give the singleton graph (igraph returns the null graph).
• Graph::lcf with n = 0 gives the null graph (igraph divides by zero), and LCF shifts and chordal ring offsets are reduced modulo the number of vertices (igraph adds them without overflow checks).
• Graph::extended_chordal_ring accepts a chord matrix without columns (igraph divides by the number of columns).

Re-exports

pub use crate::constants::AllowedEdgeTypes;

Enums

FamousGraph

The named graphs known to Graph::famous.