code: public boolean addChild(ClusteringTreeNode e) {
  		assert (this.center.length == e.center.length);
  		return this.children.add(e);
  	}
docs: Adds a child node.
  
  @param e
  the child node to add
  @return <code>true</code>
  @see java.util.List#add(java.lang.Object)