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package de.lmu.ifi.dbs.elki.math.linearalgebra.pca.weightfunctions;
/*
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/>.
*/
/**
* Exponential Weight function, scaled such that the result it 0.1 at distance
* == max
*
* stddev * exp(-.5 * distance/stddev)
*
* This is similar to the Gaussian weight function, except distance/stddev is
* not squared.
*
* @author Erich Schubert
*/
public final class ExponentialStddevWeight implements WeightFunction {
/**
* Get exponential weight, max is ignored.
*/
@Override
public double getWeight(double distance, double max, double stddev) {
if(stddev <= 0) {
return 1;
}
double scaleddistance = distance / stddev;
return stddev * java.lang.Math.exp(-.5 * scaleddistance);
}
}
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