Function graph_from 

pub fn graph_from<S, N, E, F, G>(
    nodes: &[S],
    edges: &[(S, S)],
    node_weight: F,
    edge_weight: G,
) -> Graph<N, E, Undirected, u32>
where
    S: PartialEq,
    F: FnMut(&S) -> N,
    G: FnMut(&(S, S)) -> E,

Turns the nodes and edges into a Graph. The node and edge weights are computed via the provided functions node_weight and edge_weight.