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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) 2014
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.Random;
import de.lmu.ifi.dbs.elki.database.ids.DBID;
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.math.random.RandomFactory;
import de.lmu.ifi.dbs.elki.utilities.documentation.Reference;
import de.lmu.ifi.dbs.elki.utilities.optionhandling.AbstractParameterizer;
import de.lmu.ifi.dbs.elki.utilities.optionhandling.OptionID;
import de.lmu.ifi.dbs.elki.utilities.optionhandling.parameterization.Parameterization;
import de.lmu.ifi.dbs.elki.utilities.optionhandling.parameters.RandomParameter;
/**
* Encapsulates the required methods for a split of a node in an M-Tree. The
* routing objects are chosen according to the RANDOM strategy.
*
* Note: only the routing objects are chosen at random, this is not a random
* assignment!
*
* 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 <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 RandomSplit<O, N extends AbstractMTreeNode<O, N, E>, E extends MTreeEntry> extends MTreeSplit<O, N, E> {
/**
* Random generator.
*/
private Random random;
/**
* Creates a new split object.
*/
public RandomSplit(RandomFactory rnd) {
super();
this.random = rnd.getSingleThreadedRandom();
}
/**
* Selects two objects of the specified node to be promoted and stored into
* the parent node. The m-RAD strategy considers all possible pairs of objects
* and, after partitioning the set of entries, promotes the pair of objects
* for which the sum of covering radiuses is minimum.
*
* @param tree Tree to use
* @param node the node to be split
*/
@Override
public Assignments<E> split(AbstractMTree<O, N, E, ?> tree, N node) {
int pos1 = random.nextInt(node.getNumEntries());
int pos2 = random.nextInt(node.getNumEntries() - 1);
if(pos2 >= pos1) {
++pos2;
}
DBID id1 = node.getEntry(pos1).getRoutingObjectID();
DBID id2 = node.getEntry(pos2).getRoutingObjectID();
return balancedPartition(tree, node, id1, id2);
}
/**
* Parameterization class.
*
* @author Erich Schubert
*
* @apiviz.exclude
*
* @param <O> the type of DatabaseObject to be stored 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 static class Parameterizer<O, N extends AbstractMTreeNode<O, N, E>, E extends MTreeEntry> extends AbstractParameterizer {
/**
* Option ID for the random generator.
*/
public static final OptionID RANDOM_ID = new OptionID("mtree.randomsplit.random", "Random generator / seed for the randomized split.");
/**
* Random generator
*/
RandomFactory rnd = RandomFactory.DEFAULT;
@Override
protected void makeOptions(Parameterization config) {
super.makeOptions(config);
RandomParameter rndP = new RandomParameter(RANDOM_ID);
if(config.grab(rndP)) {
rnd = rndP.getValue();
}
}
@Override
protected RandomSplit<O, N, E> makeInstance() {
return new RandomSplit<>(rnd);
}
}
}
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