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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/>.
*/
/**
* Quadratic weight function, scaled using the standard deviation.
*
* We needed another scaling here, we chose the cutoff point to be 3*stddev. If
* you need another value, you have to reimplement this class.
*
* max(0.0, 1.0 - (distance/(3*stddev))^2
*
* @author Erich Schubert
*/
public final class QuadraticStddevWeight implements WeightFunction {
/**
* Scaling: at scaling * stddev the function will hit 0.0
*/
private static final double scaling = 3;
/**
* Evaluate weight function at given parameters. max is ignored.
*/
@Override
public double getWeight(double distance, double max, double stddev) {
if(stddev <= 0) {
return 1;
}
double scaleddistance = distance / (scaling * stddev);
// After this, the result would be negative.
if(scaleddistance >= 1.0) {
return 0.0;
}
return 1.0 - scaleddistance * scaleddistance;
}
}
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