Function edge_inverse_degree_sum 

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

Compute the inverse degree-sum index over edges.

Σ_{(u,v)∈E} 1 / (d(u) + d(v))

Self-loops and edges with a zero-degree endpoint are skipped. Related to the inverse sum indeg index (ISD) but sums over edges rather than vertex neighborhoods.

Examples

use rust_igraph::{Graph, edge_inverse_degree_sum};

// K_3: 3 edges, each (2,2) → 3·(1/4) = 0.75
let g = Graph::from_edges(&[(0,1),(1,2),(0,2)], false, Some(3)).unwrap();
assert!((edge_inverse_degree_sum(&g).unwrap() - 0.75).abs() < 1e-10);