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package de.lmu.ifi.dbs.elki.math.linearalgebra.randomprojections;
/*
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/>.
*/
import de.lmu.ifi.dbs.elki.math.linearalgebra.Matrix;
import de.lmu.ifi.dbs.elki.utilities.RandomFactory;
import de.lmu.ifi.dbs.elki.utilities.documentation.Reference;
import de.lmu.ifi.dbs.elki.utilities.optionhandling.OptionID;
import de.lmu.ifi.dbs.elki.utilities.optionhandling.constraints.CommonConstraints;
import de.lmu.ifi.dbs.elki.utilities.optionhandling.parameterization.Parameterization;
import de.lmu.ifi.dbs.elki.utilities.optionhandling.parameters.DoubleParameter;
/**
* Random projections as suggested by Dimitris Achlioptas.
*
* Reference:
* <p>
* Database-friendly random projections: Johnson-Lindenstrauss with binary coins
* <br />
* Dimitris Achlioptas<br />
* In: Proceedings of the twentieth ACM SIGMOD-SIGACT-SIGART symposium on
* Principles of database systems
* </p>
*
* @author Erich Schubert
*/
@Reference(title = "Database-friendly random projections: Johnson-Lindenstrauss with binary coins", authors = "Dimitris Achlioptas", booktitle = "Proceedings of the twentieth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems", url = "http://dx.doi.org/10.1145/375551.375608")
public class AchlioptasRandomProjectionFamily extends AbstractRandomProjectionFamily {
/**
* Projection sparsity.
*/
private double sparsity;
/**
* Constructor.
*
* @param sparsity Projection sparsity
* @param random Random number generator.
*/
public AchlioptasRandomProjectionFamily(double sparsity, RandomFactory random) {
super(random);
this.sparsity = sparsity;
}
@Override
public Projection generateProjection(int idim, int odim) {
final double pPos = .5 / sparsity;
final double pNeg = pPos + pPos; // Threshold
double baseValuePart = Math.sqrt(this.sparsity);
Matrix projectionMatrix = new Matrix(odim, idim);
for(int i = 0; i < odim; ++i) {
for(int j = 0; j < idim; ++j) {
final double r = random.nextDouble();
final double value;
if(r < pPos) {
value = baseValuePart;
}
else if(r < pNeg) {
value = -baseValuePart;
}
else {
value = 0.;
}
projectionMatrix.set(i, j, value);
}
}
return new MatrixProjection(projectionMatrix);
}
/**
* Parameterization class.
*
* @author Erich Schubert
*
* @apiviz.exclude
*/
public static class Parameterizer extends AbstractRandomProjectionFamily.Parameterizer {
/**
* Parameter for the projection sparsity.
*/
public static final OptionID SPARSITY_ID = new OptionID("achlioptas.sparsity", "Frequency of zeros in the projection matrix.");
/**
* Projection sparsity
*/
private double sparsity = 3.;
@Override
protected void makeOptions(Parameterization config) {
super.makeOptions(config);
DoubleParameter sparsP = new DoubleParameter(SPARSITY_ID);
sparsP.setDefaultValue(3.);
sparsP.addConstraint(CommonConstraints.GREATER_EQUAL_ONE_DOUBLE);
if(config.grab(sparsP)) {
sparsity = sparsP.doubleValue();
}
}
@Override
protected AchlioptasRandomProjectionFamily makeInstance() {
return new AchlioptasRandomProjectionFamily(sparsity, random);
}
}
}
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