Function first_inverse_nirmala 

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

Compute the first inverse Nirmala index.

IN₁(G) = Σ_{(u,v)∈E} 1/√(d(u) + d(v))

Self-loops and edges where both endpoints have degree 0 are skipped.

Examples

use rust_igraph::{Graph, first_inverse_nirmala};

// K_3: 3 edges × 1/√4 = 3×0.5 = 1.5
let g = Graph::from_edges(&[(0,1),(1,2),(0,2)], false, Some(3)).unwrap();
assert!((first_inverse_nirmala(&g).unwrap() - 1.5).abs() < 1e-10);