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package de.lmu.ifi.dbs.elki.index.tree.metrical.mtreevariants.mktrees.mkcop;
/*
This file is part of ELKI:
Environment for Developing KDD-Applications Supported by Index-Structures
Copyright (C) 2012
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.io.Externalizable;
import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectOutput;
import de.lmu.ifi.dbs.elki.database.query.distance.DistanceQuery;
import de.lmu.ifi.dbs.elki.distance.distancevalue.NumberDistance;
/**
* Provides an approximation for knn-distances line consisting of incline m,
* axes intercept t and a start value for k.
*
* @author Elke Achtert
*/
public class ApproximationLine implements Externalizable {
private static final long serialVersionUID = 1;
/**
* The incline.
*/
private double m;
/**
* The axes intercept.
*/
private double t;
/**
* The start value for k.
*/
private int k_0;
/**
* Empty constructor for serialization purposes.
*/
public ApproximationLine() {
// empty constructor
}
/**
* Provides an approximation for knn-distances line consisting of incline m,
* axes intercept t and a start value for k.
*
* @param k_0 the start value for k
* @param m the incline
* @param t the axes intercept
*/
public ApproximationLine(int k_0, double m, double t) {
this.k_0 = k_0;
this.m = m;
this.t = t;
}
/**
* Returns the incline.
*
* @return the incline
*/
public double getM() {
return m;
}
/**
* Returns the axes intercept.
*
* @return the axes intercept
*/
public double getT() {
return t;
}
/**
* Returns the start value for k.
*
* @return the start value for k
*/
public int getK_0() {
return k_0;
}
/**
* Returns the function value of the approximation line at the specified k.
*
* @param k the value for which the function value of the approximation line
* should be returned
* @return the function value of the approximation line at the specified k
*/
public double getValueAt(int k) {
if(k < k_0) {
return Double.POSITIVE_INFINITY;
}
return m * StrictMath.log(k) + t;
}
/**
* Returns the approximated knn-distance at the specified k.
*
* @param <O> Object type
* @param <D> Distance type
* @param k the value for which the knn-distance should be returned
* @param distanceFunction the distance function
* @return the approximated knn-distance at the specified k
*/
public <O, D extends NumberDistance<D, ?>> D getApproximatedKnnDistance(int k, DistanceQuery<O, D> distanceFunction) {
if(k < k_0) {
return distanceFunction.nullDistance();
}
return distanceFunction.getDistanceFactory().parseString("" + StrictMath.exp(getValueAt(k)));
}
/**
* The object implements the writeExternal method to save its contents by
* calling the methods of DataOutput for its primitive values or calling the
* writeObject method of ObjectOutput for objects, strings, and arrays.
*
* @param out the stream to write the object to
*/
@Override
public void writeExternal(ObjectOutput out) throws IOException {
out.writeDouble(m);
out.writeDouble(t);
}
/**
* The object implements the readExternal method to restore its contents by
* calling the methods of DataInput for primitive types and readObject for
* objects, strings and arrays. The readExternal method must read the values
* in the same sequence and with the same types as were written by
* writeExternal.
*
* @param in the stream to read data from in order to restore the object
*/
@Override
public void readExternal(ObjectInput in) throws IOException {
m = in.readDouble();
t = in.readDouble();
}
/**
* Returns true</code> if this object is the same as the o argument;
* <code>false</code> otherwise.
*
* @param o the reference object with which to compare.
* @return <code>true</code> if this object is the same as the obj argument;
* <code>false</code> otherwise.
*/
@Override
public boolean equals(Object o) {
if(this == o) {
return true;
}
if(o == null || getClass() != o.getClass()) {
return false;
}
final ApproximationLine that = (ApproximationLine) o;
return Double.compare(that.m, m) == 0 && Double.compare(that.t, t) == 0;
}
/**
* Returns a hash code value for this object
*
* @return a hash code value for this object.
*/
@Override
public int hashCode() {
int result;
long temp;
temp = m != 0.0d ? Double.doubleToLongBits(m) : 0L;
result = (int) (temp ^ (temp >>> 32));
temp = t != 0.0d ? Double.doubleToLongBits(t) : 0L;
result = 29 * result + (int) (temp ^ (temp >>> 32));
return result;
}
/**
* Returns a string representation of the object.
*
* @return a string representation of the object.
*/
@Override
public String toString() {
return "m = " + m + ", t = " + t + " k_0 " + k_0;
}
}
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