Function degree_neighbor_range_sum 

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

Compute the sum of neighbor degree ranges.

Σ_{v: d(v)>0} (max_{u ∈ N(v)} d(u) - min_{u ∈ N(v)} d(u))

For each non-isolated vertex, computes the range (max - min) of neighbor degrees and sums them. Returns 0 for edgeless or regular graphs.

Examples

use rust_igraph::{Graph, degree_neighbor_range_sum};

// K_3: each vertex sees [2,2] → range 0 → sum 0
let g = Graph::from_edges(&[(0,1),(1,2),(0,2)], false, Some(3)).unwrap();
assert_eq!(degree_neighbor_range_sum(&g).unwrap(), 0);