Function degree_neighbor_max_sum 

pub fn degree_neighbor_max_sum(graph: &Graph) -> IgraphResult<u64>

Compute the sum of maximum neighbor degrees.

Σ_{v: d(v)>0} max_{u ∈ N(v)} d(u)

For each non-isolated vertex, finds the highest degree among its neighbors and sums these maxima. Returns 0 for edgeless graphs.

Examples

use rust_igraph::{Graph, degree_neighbor_max_sum};

// Star S_5: center max=1, 4 leaves max=4 → 1 + 4·4 = 17
let g = Graph::from_edges(&[(0,1),(0,2),(0,3),(0,4)], false, Some(5)).unwrap();
assert_eq!(degree_neighbor_max_sum(&g).unwrap(), 17);