Function difference 

pub fn difference(orig: &Graph, sub: &Graph) -> IgraphResult<Graph>

Returns orig \ sub: the multiset difference of the edges.

The result has orig.vcount() vertices — vertices in sub beyond orig.vcount() are simply ignored. For each endpoint pair (u, v), the multiplicity in the result equals max(0, count_orig - count_sub).

Both inputs must agree on directedness; an undirected edge (u, v) is canonicalised to (min(u, v), max(u, v)) before counting, while directed edges are tallied as-is.

Output edges are emitted in lexicographic (src, tgt) order; two edges sharing the same canonicalised pair appear consecutively.

Errors

• IgraphError::InvalidArgument if directedness diverges.

Examples

use rust_igraph::{Graph, difference};

// Triangle \ path: edges {(0,1), (1,2), (2,0)} \ {(0,1), (1,2)}
// → {(0,2)} on 3 vertices (canonicalised (0,2) for undirected).
let mut a = Graph::with_vertices(3);
a.add_edge(0, 1).unwrap();
a.add_edge(1, 2).unwrap();
a.add_edge(2, 0).unwrap();
let mut b = Graph::with_vertices(3);
b.add_edge(0, 1).unwrap();
b.add_edge(1, 2).unwrap();

let d = difference(&a, &b).unwrap();
assert_eq!(d.vcount(), 3);
assert_eq!(d.ecount(), 1);