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package de.lmu.ifi.dbs.elki.utilities.scaling.outlier;
/*
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 de.lmu.ifi.dbs.elki.database.ids.DBID;
import de.lmu.ifi.dbs.elki.result.outlier.OutlierResult;
import de.lmu.ifi.dbs.elki.utilities.documentation.Reference;
/**
* Scaling function to invert values basically by computing 1/x, but in a variation
* that maps the values to the [0:1] interval and avoiding division by 0.
*
* The exact formula can be written as
*
* 1 / (value * max_{x!=0}(1 / abs(x))) = min_{x != 0}(abs(x)) / x
*
* with 1 / 0 := 1
*
* @author Erich Schubert
*/
@Reference(authors="H.-P. Kriegel, P. Kröger, E. Schubert, A. Zimek", title="Interpreting and Unifying Outlier Scores", booktitle="Proc. 11th SIAM International Conference on Data Mining (SDM), Mesa, AZ, 2011", url="http://www.dbs.ifi.lmu.de/~zimek/publications/SDM2011/SDM11-outlier-preprint.pdf")
public class MultiplicativeInverseScaling implements OutlierScalingFunction {
/**
* Constructor, adhering to
* {@link de.lmu.ifi.dbs.elki.utilities.optionhandling.Parameterizable}
*/
public MultiplicativeInverseScaling() {
super();
}
/**
* Scaling value, set by {@link #prepare}.
*/
double scaleval = 0;
@Override
public double getScaled(double value) {
assert (scaleval != 0) : "prepare() was not run prior to using the scaling function.";
try {
return 1.0 / (value * scaleval);
}
catch(ArithmeticException e) {
return 1.0;
}
}
@Override
public void prepare(OutlierResult or) {
scaleval = getScaleValue(or);
}
/**
* Compute the scaling value in a linear scan over the annotation.
*
* @param or Outlier result
* @return Scaling value.
*/
private static double getScaleValue(OutlierResult or) {
double max = Double.MIN_VALUE;
for(DBID id : or.getScores().iterDBIDs()) {
double val = or.getScores().get(id);
double inv = Math.abs(1.0 / val);
if(!Double.isInfinite(inv) && !Double.isNaN(inv)) {
max = Math.max(max, inv);
}
}
return max;
}
@Override
public double getMin() {
return 0.0;
}
@Override
public double getMax() {
return 1.0;
}
}
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