Function first_gourava_index 

pub fn first_gourava_index(graph: &Graph) -> IgraphResult<u64>

Compute the first Gourava index.

GO₁(G) = Σ_{(u,v)∈E} [d(u) + d(v) + d(u)·d(v)]

Self-loops are skipped.

Examples

use rust_igraph::{Graph, first_gourava_index};

// K_3: each edge (2+2+4)=8, 3 edges → 24
let g = Graph::from_edges(&[(0,1),(1,2),(0,2)], false, Some(3)).unwrap();
assert_eq!(first_gourava_index(&g).unwrap(), 24);