optimal.community() was renamed to cluster_optimal() to create a more
consistent API.
optimal.community(graph, weights = NULL)The input graph. It may be undirected or directed.
The weights of the edges. It must be a positive numeric
vector, NULL or NA. If it is NULL and the input graph has a
‘weight’ edge attribute, then that attribute will be used. If
NULL and no such attribute is present, then the edges will have equal
weights. Set this to NA if the graph was a ‘weight’ edge
attribute, but you don't want to use it for community detection. A larger
edge weight means a stronger connection for this function.