package de.lmu.ifi.dbs.elki.distance.distancefunction;
/*
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.BitSet;
import de.lmu.ifi.dbs.elki.data.NumberVector;
import de.lmu.ifi.dbs.elki.data.SparseNumberVector;
import de.lmu.ifi.dbs.elki.database.query.distance.PrimitiveDistanceQuery;
import de.lmu.ifi.dbs.elki.database.relation.Relation;
import de.lmu.ifi.dbs.elki.distance.distancevalue.DoubleDistance;
import de.lmu.ifi.dbs.elki.math.linearalgebra.Vector;
/**
* Abstract base class for Cosine and ArcCosine distances.
*
* @author Erich Schubert
*/
public abstract class AbstractCosineDistanceFunction extends AbstractVectorDoubleDistanceFunction {
/**
* Constructor.
*/
public AbstractCosineDistanceFunction() {
super();
}
/**
* Compute the angle between two vectors.
*
* @param v1 first vector
* @param v2 second vector
* @return Angle
*/
protected double angle(NumberVector<?, ?> v1, NumberVector<?, ?> v2) {
if(v1 instanceof SparseNumberVector<?, ?> && v2 instanceof SparseNumberVector<?, ?>) {
return angleSparse((SparseNumberVector<?, ?>) v1, (SparseNumberVector<?, ?>) v2);
}
Vector m1 = v1.getColumnVector();
m1.normalize();
Vector m2 = v2.getColumnVector();
m2.normalize();
return m1.transposeTimes(m2);
}
/**
* Compute the angle for sparse vectors.
*
* @param v1 First vector
* @param v2 Second vector
* @return angle
*/
protected double angleSparse(SparseNumberVector<?, ?> v1, SparseNumberVector<?, ?> v2) {
BitSet b1 = v1.getNotNullMask();
BitSet b2 = v2.getNotNullMask();
BitSet both = (BitSet) b1.clone();
both.and(b2);
// Length of first vector
double l1 = 0.0;
for(int i = b1.nextSetBit(0); i >= 0; i = b1.nextSetBit(i + 1)) {
final double val = v1.doubleValue(i);
l1 += val * val;
}
l1 = Math.sqrt(l1);
// Length of second vector
double l2 = 0.0;
for(int i = b2.nextSetBit(0); i >= 0; i = b2.nextSetBit(i + 1)) {
final double val = v2.doubleValue(i);
l2 += val * val;
}
l2 = Math.sqrt(l2);
// Cross product
double cross = 0.0;
for(int i = both.nextSetBit(0); i >= 0; i = both.nextSetBit(i + 1)) {
cross += v1.doubleValue(i) * v2.doubleValue(i);
}
return cross / (l1 * l2);
}
@Override
public <T extends NumberVector<?, ?>> PrimitiveDistanceQuery<T, DoubleDistance> instantiate(Relation<T> relation) {
return new PrimitiveDistanceQuery<T, DoubleDistance>(relation, this);
}
}