Function reduced_sum_connectivity 

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

Compute the reduced sum-connectivity index.

χ_red(G) = Σ_{(u,v)∈E} 1/√((du-1)+(dv-1))

Edges where du + dv - 2 == 0 (both endpoints degree 1) are skipped. Self-loops are skipped.

Examples

use rust_igraph::{Graph, reduced_sum_connectivity};

// K_3: 3 edges, d=(2,2), each 1/√(1+1)=1/√2 → 3/√2
let g = Graph::from_edges(&[(0,1),(1,2),(0,2)], false, Some(3)).unwrap();
let expected = 3.0 / 2.0_f64.sqrt();
assert!((reduced_sum_connectivity(&g).unwrap() - expected).abs() < 1e-10);