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package de.lmu.ifi.dbs.elki.index.tree.metrical.mtreevariants.mktrees.mkapp;
/*
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.utilities.FormatUtil;
/**
* Provides an polynomial approximation bo + b1*k + b2*k^2 + ... + bp*k^p
* for knn-distances consisting of parameters b0, ..., bp.
*
* @author Elke Achtert
*/
public class PolynomialApproximation implements Externalizable {
private static final long serialVersionUID = 1;
/**
* The parameters b0, ..., bp.
*/
private double[] b;
/**
* Empty constructor for serialization purposes.
*/
public PolynomialApproximation() {
// empty constructor
}
/**
* Provides an polynomial approximation bo + b1*k + b2*k^2 + ... + bp*k^p
* for knn-distances consisting of parameters b0, ..., bp.
*
* @param b the parameters b0, ..., bi
*/
public PolynomialApproximation(double[] b) {
this.b = b;
}
/**
* Returns the parameter bp at the specified index p.
*
* @param p the index
* @return the parameter bp at the specified index p
*/
public double getB(int p) {
return b[p];
}
/**
* Returns a copy of the the array of coefficients b0, ..., bp.
* @return the a copy of the array of coefficients b0, ..., bp
*/
public double[] getCoefficients() {
double[] result = new double[b.length];
System.arraycopy(b, 0, result, 0, b.length);
return result;
}
/**
* Returns the order of the polynom.
*
* @return the order of the polynom
*/
public int getPolynomialOrder() {
return b.length;
}
/**
* Returns the function value of the polynoial approximation
* at the specified k.
*
* @param k the value for which the polynoial approximation should be returned
* @return the function value of the polynoial approximation
* at the specified k
*/
public double getValueAt(int k) {
double result = 0;
double log_k = Math.log(k);
for (int p = 0; p < b.length; p++) {
result += b[p] * Math.pow(log_k, p);
}
return result;
}
/**
* 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.writeInt(b.length);
for (double aB : b) {
out.writeDouble(aB);
}
}
/**
* 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 {
b = new double[in.readInt()];
for (int p = 0; p < b.length; p++) {
b[p] = in.readDouble();
}
}
/**
* Returns a string representation of the object.
*
* @return a string representation of the object.
*/
@Override
public String toString() {
return FormatUtil.format(b, 4);
}
}
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