# Function bevy::utils::petgraph::operator::complement

``````pub fn complement<N, E, Ty, Ix>(
input: &Graph<N, E, Ty, Ix>,
output: &mut Graph<N, E, Ty, Ix>,
weight: E
)where
Ty: EdgeType,
Ix: IndexType,
E: Clone,
N: Clone,``````
Expand description

[Generic] complement of the graph

Computes the graph complement of the input Graph and stores it in the provided empty output Graph.

The function does not create self-loops.

Computes in O(|V|^2*log(|V|)) time (average).

Returns the complement.

## Example

``````use petgraph::Graph;
use petgraph::operator::complement;
use petgraph::prelude::*;

let mut graph: Graph<(),(),Directed> = Graph::new();
let a = graph.add_node(()); // node with no weight
let b = graph.add_node(());
let c = graph.add_node(());
let d = graph.add_node(());

graph.extend_with_edges(&[
(a, b),
(b, c),
(c, d),
]);
// a ----> b ----> c ----> d

let mut output: Graph<(), (), Directed> = Graph::new();

complement(&graph, &mut output, ());

let mut expected_res: Graph<(), (), Directed> = Graph::new();
let a = expected_res.add_node(());
let b = expected_res.add_node(());
let c = expected_res.add_node(());
let d = expected_res.add_node(());
expected_res.extend_with_edges(&[
(a, c),
(a, d),
(b, a),
(b, d),
(c, a),
(c, b),
(d, a),
(d, b),
(d, c),
]);

for x in graph.node_indices() {
for y in graph.node_indices() {
assert_eq!(output.contains_edge(x, y), expected_res.contains_edge(x, y));
}
}``````