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package de.lmu.ifi.dbs.elki.index.tree.metrical.mtreevariants.strategies.split;
/*
This file is part of ELKI:
Environment for Developing KDD-Applications Supported by Index-Structures
Copyright (C) 2013
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 de.lmu.ifi.dbs.elki.database.ids.DBID;
import de.lmu.ifi.dbs.elki.distance.distancevalue.NumberDistance;
import de.lmu.ifi.dbs.elki.index.tree.metrical.mtreevariants.AbstractMTree;
import de.lmu.ifi.dbs.elki.index.tree.metrical.mtreevariants.AbstractMTreeNode;
import de.lmu.ifi.dbs.elki.index.tree.metrical.mtreevariants.MTreeEntry;
import de.lmu.ifi.dbs.elki.utilities.documentation.Reference;
/**
* 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.
*
* Reference:
* <p>
* P. Ciaccia, M. Patella, P. Zezula<br />
* M-tree: An Efficient Access Method for Similarity Search in Metric Spaces<br />
* In Proceedings of 23rd International Conference on Very Large Data Bases
* (VLDB'97), August 25-29, 1997, Athens, Greece
* </p>
*
* @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
*/
@Reference(authors = "P. Ciaccia, M. Patella, P. Zezula", title = "M-tree: An Efficient Access Method for Similarity Search in Metric Spaces", booktitle = "VLDB'97, Proceedings of 23rd International Conference on Very Large Data Bases, August 25-29, 1997, Athens, Greece", url = "http://www.vldb.org/conf/1997/P426.PDF")
public class MLBDistSplit<O, D extends NumberDistance<D, ?>, N extends AbstractMTreeNode<O, D, N, E>, E extends MTreeEntry> extends MTreeSplit<O, D, N, E> {
/**
* Creates a new split object.
*/
public MLBDistSplit() {
super();
}
/**
* 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 tree Tree to use
* @param node the node to be split
*/
@Override
public Assignments<E> split(AbstractMTree<O, D, N, E, ?> tree, N node) {
DBID firstPromoted = null;
DBID secondPromoted = null;
// choose first and second routing object
double currentMaxDist = 0.;
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();
double distance = tree.distance(id1, id2).doubleValue();
if (distance >= currentMaxDist) {
firstPromoted = id1;
secondPromoted = id2;
currentMaxDist = distance;
}
}
}
return balancedPartition(tree, node, firstPromoted, secondPromoted);
}
}
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