package de.lmu.ifi.dbs.elki.index.tree.metrical.mtreevariants.split;
/*
This file is part of ELKI:
Environment for Developing KDD-Applications Supported by Index-Structures
Copyright (C) 2011
Ludwig-Maximilians-Universität München
Lehr- und Forschungseinheit für Datenbanksysteme
ELKI Development Team
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU Affero General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU Affero General Public License for more details.
You should have received a copy of the GNU Affero General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import de.lmu.ifi.dbs.elki.database.ids.DBID;
import de.lmu.ifi.dbs.elki.database.query.distance.DistanceQuery;
import de.lmu.ifi.dbs.elki.distance.distancevalue.Distance;
import de.lmu.ifi.dbs.elki.index.tree.DistanceEntry;
import de.lmu.ifi.dbs.elki.index.tree.metrical.mtreevariants.AbstractMTreeNode;
import de.lmu.ifi.dbs.elki.index.tree.metrical.mtreevariants.MTreeEntry;
/**
* Encapsulates the required methods for a split of a node in an M-Tree. The
* routing objects are chosen according to the M_LB_DIST strategy.
*
* @author Elke Achtert
* @param <O> the type of DatabaseObject to be stored in the M-Tree
* @param <D> the type of Distance used in the M-Tree
* @param <N> the type of AbstractMTreeNode used in the M-Tree
* @param <E> the type of MetricalEntry used in the M-Tree
*/
public class MLBDistSplit<O, D extends Distance<D>, N extends AbstractMTreeNode<O, D, N, E>, E extends MTreeEntry<D>> extends MTreeSplit<O, D, N, E> {
/**
* Creates a new split object.
*
* @param node the node to be split
* @param distanceFunction the distance function
*/
public MLBDistSplit(N node, DistanceQuery<O, D> distanceFunction) {
super();
promote(node, distanceFunction);
}
/**
* Selects the second object of the specified node to be promoted and stored
* into the parent node and partitions the entries according to the M_LB_DIST
* strategy.
* <p/>
* This strategy considers all possible pairs of objects and chooses the pair
* of objects for which the distance is maximum.
*
* @param node the node to be split
* @param distanceFunction the distance function
*/
private void promote(N node, DistanceQuery<O, D> distanceFunction) {
DBID firstPromoted = null;
DBID secondPromoted = null;
// choose first and second routing object
D currentMaxDist = distanceFunction.nullDistance();
for(int i = 0; i < node.getNumEntries(); i++) {
DBID id1 = node.getEntry(i).getRoutingObjectID();
for(int j = i + 1; j < node.getNumEntries(); j++) {
DBID id2 = node.getEntry(j).getRoutingObjectID();
D distance = distanceFunction.distance(id1, id2);
if(distance.compareTo(currentMaxDist) >= 0) {
firstPromoted = id1;
secondPromoted = id2;
currentMaxDist = distance;
}
}
}
// partition the entries
List<DistanceEntry<D, E>> list1 = new ArrayList<DistanceEntry<D, E>>();
List<DistanceEntry<D, E>> list2 = new ArrayList<DistanceEntry<D, E>>();
for(int i = 0; i < node.getNumEntries(); i++) {
DBID id = node.getEntry(i).getRoutingObjectID();
D d1 = distanceFunction.distance(firstPromoted, id);
D d2 = distanceFunction.distance(secondPromoted, id);
list1.add(new DistanceEntry<D, E>(node.getEntry(i), d1, i));
list2.add(new DistanceEntry<D, E>(node.getEntry(i), d2, i));
}
Collections.sort(list1);
Collections.sort(list2);
assignments = balancedPartition(node, firstPromoted, secondPromoted, distanceFunction);
}
}