code: def cluster(self, linkageMethod="single"):
      
      if self._overlaps is None:
        self._populateOverlaps()
      overlaps = self._overlaps
  
      linkage = scipy.cluster.hierarchy.linkage(-overlaps, method=linkageMethod)
      self._linkage = linkage
docs: Perform hierarchical clustering on training vectors using specified linkage
      method. Results can be obtained using getLinkageMatrix(), etc.
      
      @param linkageMethod (string) Linkage method for computing between-class
          dissimilarities. Valid options are: "single" (aka min), "complete"
          (aka max), "average", and "weighted". For more information, see
          http://docs.scipy.org/doc/scipy-0.16.0/reference/generated/scipy.cluster.hierarchy.linkage.html