I have a graph with 39 nodes. Nodes number 32, 33 and 37 have a specific property(Black start power plant). I want to cluster the graph to 3 clusters by the k-medoids method.How can I cluster the graph such that none of the nodes numbered 32, 33 and 37 belong to the similar clusters?In other words,I want to perform clustering such that foregoing nodes be as a center of each 3 clusters and each cluster include more than one node.