Function variable_sum_exdeg 

pub fn variable_sum_exdeg(graph: &Graph, a: f64) -> IgraphResult<f64>

Compute the variable sum exdeg index.

SEI_a(G) = Σ_v d(v) · a^{d(v)} for a > 0, a ≠ 1.

Returns 0.0 for empty graphs or when a ≤ 0.

Examples

use rust_igraph::{Graph, variable_sum_exdeg};

// K_3: d=(2,2,2), a=2 → 3·2·4 = 24
let g = Graph::from_edges(&[(0,1),(1,2),(0,2)], false, Some(3)).unwrap();
assert!((variable_sum_exdeg(&g, 2.0).unwrap() - 24.0).abs() < 1e-10);