Function first_redefined_zagreb 

pub fn first_redefined_zagreb(graph: &Graph) -> IgraphResult<f64>

Compute the first redefined Zagreb index.

ReZG₁(G) = Σ_{(u,v)∈E} (d(u) + d(v)) / (d(u) · d(v))

Edges where either endpoint has degree 0 or self-loops are skipped.

Examples

use rust_igraph::{Graph, first_redefined_zagreb};

// K_3: each edge (2+2)/(2·2)=1, 3 edges → 3
let g = Graph::from_edges(&[(0,1),(1,2),(0,2)], false, Some(3)).unwrap();
assert!((first_redefined_zagreb(&g).unwrap() - 3.0).abs() < 1e-10);