Function symmetric_division_deg_index 

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

Compute the symmetric division deg index.

SDD(G) = Σ_{(u,v)∈E} (d_u² + d_v²) / (d_u · d_v)

Equivalently, each edge contributes d_u/d_v + d_v/d_u. For regular graphs every edge contributes 2, so SDD = 2m.

Self-loops are skipped. Edges with d_u · d_v = 0 are skipped.

Examples

use rust_igraph::{Graph, symmetric_division_deg_index};

// K_3: all degrees 2 → each edge contributes 2, SDD = 6
let g = Graph::from_edges(&[(0,1),(1,2),(0,2)], false, Some(3)).unwrap();
assert!((symmetric_division_deg_index(&g).unwrap() - 6.0).abs() < 1e-10);