Function distance_estrada_index 

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

Compute the distance Estrada index DEE = Σ exp(λ_i(D)).

Examples

use rust_igraph::{Graph, distance_estrada_index};

// K_3: eigenvalues {2, -1, -1}, DEE = e^2 + 2e^{-1}
let g = Graph::from_edges(&[(0,1),(1,2),(0,2)], false, Some(3)).unwrap();
let dee = distance_estrada_index(&g).unwrap();
let expected = 2.0_f64.exp() + 2.0 * (-1.0_f64).exp();
assert!((dee - expected).abs() < 0.1);