Function lexicographic_product 

pub fn lexicographic_product(g1: &Graph, g2: &Graph) -> IgraphResult<Graph>

Computes the lexicographic product of two graphs.

The result has |V1| * |V2| vertices. Vertex (i, j) is identified by i * |V2| + j. An edge exists between (i, j) and (k, l) iff:

• (i, k) is an edge in g1 (regardless of j and l), OR
• i == k and (j, l) is an edge in g2.

Note: unlike the other products, the lexicographic product is NOT commutative.

Both graphs must have the same directedness.

Arguments

• g1 — the first factor graph (outer).
• g2 — the second factor graph (inner).

Errors

Returns InvalidArgument if the graphs differ in directedness, or if the product vertex count overflows u32.

Examples

use rust_igraph::{Graph, lexicographic_product};

let mut g1 = Graph::with_vertices(2);
g1.add_edge(0, 1).unwrap();
let g2 = Graph::with_vertices(3); // 3 isolated vertices

let p = lexicographic_product(&g1, &g2).unwrap();
assert_eq!(p.vcount(), 6);
// 1 edge in g1 × 3² = 9 cross-edges (undirected, so 9 unique pairs)
assert_eq!(p.ecount(), 9);