(L, M) = leaders(Z, T):
Returns the root nodes in a hierarchical clustering corresponding to a cut defined by a flat cluster assignment vector T. See the fcluster function for more information on the format of T.
For each flat cluster of the flat clusters represented in the nsized flat cluster assignment vector T, this function finds the lowest cluster node in the linkage tree Z such that:
 leaf descendents belong only to flat cluster j (i.e. T[p]==j for all in where is the set of leaf ids of leaf nodes descendent with cluster node )
 there does not exist a leaf that is not descendent with that also belongs to cluster (i.e. T[q]!=j for all not in ). If this condition is violated, T is not a valid cluster assignment vector, and an exception will be thrown.
Arguments : 


Returns :  (L, M)
