docs: private HashSparseVector calculateCentroid (ArrayList<Instance> insts) {
  		HashSparseVector centroid = new HashSparseVector();
  		
  		
  		Iterator i = insts.iterator();
  
  		while (i.hasNext()) {
  			Instance d = (Instance) i.next();
  
  			centroid.plus((HashSparseVector) d.getData());
  		}
  		centroid.scaleDivide(insts.size());
  
  		return centroid;
  	}