Function coverage 

pub fn coverage(
    edges: &[(usize, usize, f64)],
    n_nodes: usize,
    communities: &[usize],
) -> f64

Compute coverage: the fraction of edge weight inside communities.

coverage = Σ_{intra} w_{ij} / Σ_{all} w_{ij}

Arguments

• edges – Weighted edge list.
• n_nodes – Total number of nodes.
• communities – Community assignment for each node.