Function isomorphic 

pub fn isomorphic(graph1: &Graph, graph2: &Graph) -> IgraphResult<bool>

Decide whether two graphs are isomorphic, choosing a backend automatically.

Mirrors igraph_isomorphic: the dispatch picks whichever engine fits the input. Only the Boolean verdict is returned — call isomorphic_vf2 or isomorphic_bliss directly when you also need the vertex mapping.

The dispatch is:

1. directed vs. undirected → IgraphError::InvalidArgument;
2. if either graph has multi-edges, both are reduced with simplify_and_colorize and compared by colour-aware VF2 (self-loops become vertex colours, parallel-edge multiplicities become edge colours);
3. otherwise, differing vertex or edge counts → false;
4. otherwise the canonical-form (BLISS) test decides.

Upstream takes an O(1) precomputed-isoclass shortcut for tiny graphs (directed 3–4, undirected 3–6 vertices) before falling back to BLISS; the canonical-form test returns the identical verdict, so this port uses it uniformly. Self-loops are supported (folded into the BLISS vertex invariant).

Errors

Returns IgraphError::InvalidArgument if the two graphs differ in directedness. Propagates backend errors otherwise.

Examples

use rust_igraph::{Graph, isomorphic};

// A 4-cycle and its relabelling are isomorphic.
let mut a = Graph::new(4, false).unwrap();
for (u, v) in [(0, 1), (1, 2), (2, 3), (3, 0)] {
    a.add_edge(u, v).unwrap();
}
let mut b = Graph::new(4, false).unwrap();
for (u, v) in [(0, 2), (2, 1), (1, 3), (3, 0)] {
    b.add_edge(u, v).unwrap();
}
assert!(isomorphic(&a, &b).unwrap());

// A 4-cycle is not isomorphic to a path on 4 vertices.
let mut p = Graph::new(4, false).unwrap();
for (u, v) in [(0, 1), (1, 2), (2, 3)] {
    p.add_edge(u, v).unwrap();
}
assert!(!isomorphic(&a, &p).unwrap());