Function inverse_degree_index 

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

Compute the inverse degree index (zeroth-order Randić index).

ID(G) = Σ_{v∈V, d(v)≥1} 1/d(v)

Isolated vertices are excluded.

Examples

use rust_igraph::{Graph, inverse_degree_index};

// Star S_4: degrees [4,1,1,1,1] → ID = 1/4 + 4·1 = 4.25
let g = Graph::from_edges(&[(0,1),(0,2),(0,3),(0,4)], false, Some(5)).unwrap();
assert!((inverse_degree_index(&g).unwrap() - 4.25).abs() < 1e-10);