Function second_zagreb_connection 

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

Compute the second Zagreb connection index.

ZC₂(G) = Σ_{(u,v)∈E} τ(u) · τ(v)

Examples

use rust_igraph::{Graph, second_zagreb_connection};

// Path 0-1-2: τ=[1,0,1]
// (0,1): 1·0=0, (1,2): 0·1=0 → ZC₂=0
let g = Graph::from_edges(&[(0,1),(1,2)], false, Some(3)).unwrap();
assert!((second_zagreb_connection(&g).unwrap()).abs() < 1e-10);