Function is_graphical 

pub fn is_graphical(
    out_degrees: &[u32],
    in_degrees: Option<&[u32]>,
    edge_types: EdgeTypeFilter,
) -> bool

Test whether a degree sequence is graphical (realizable as some graph).

For undirected graphs, pass in_degrees = None. For directed graphs, pass out_degrees and Some(in_degrees).

Algorithms

• Simple undirected: Erdős–Gallai theorem (Cloteaux 2015 linear-time).
• Loopy-simple undirected: Cairns–Mendan modification of Erdős–Gallai.
• Loopless multi undirected: even sum + sum ≥ 2·max.
• Loopy multi undirected: even sum only.
• Simple directed: Fulkerson–Chen–Anstee theorem (Berger 2014 relaxation).
• Loopy-simple directed: reduces to bigraphical simple (Gale–Ryser).
• Loopless multi directed: sum_in == sum_out + sum_out >= max_total.
• Loopy multi directed: sum_in == sum_out only.

Examples

use rust_igraph::{EdgeTypeFilter, is_graphical};

// Star K_{1,4}: center has degree 4, leaves have degree 1
assert!(is_graphical(&[4, 1, 1, 1, 1], None, EdgeTypeFilter::Simple));

// Odd sum → not graphical
assert!(!is_graphical(&[3, 1, 1], None, EdgeTypeFilter::Simple));