Calculates the cophenetic distances between each observation in the hierarchical clustering defined by the linkage Z.
Suppose p and q are original observations in disjoint clusters s and t, respectively and s and t are joined by a direct parent cluster u. The cophenetic distance between observations i and j is simply the distance between clusters s and t.
Parameters :  Z : ndarray
Y : ndarray (optional)


Returns :  c : ndarray
d : ndarray
