package de.lmu.ifi.dbs.elki.utilities.referencepoints;
/*
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.util.ArrayList;
import java.util.Collection;
import de.lmu.ifi.dbs.elki.data.NumberVector;
import de.lmu.ifi.dbs.elki.database.relation.Relation;
import de.lmu.ifi.dbs.elki.utilities.DatabaseUtil;
import de.lmu.ifi.dbs.elki.utilities.optionhandling.AbstractParameterizer;
import de.lmu.ifi.dbs.elki.utilities.optionhandling.OptionID;
import de.lmu.ifi.dbs.elki.utilities.optionhandling.constraints.GreaterEqualConstraint;
import de.lmu.ifi.dbs.elki.utilities.optionhandling.parameterization.Parameterization;
import de.lmu.ifi.dbs.elki.utilities.optionhandling.parameters.DoubleParameter;
import de.lmu.ifi.dbs.elki.utilities.pairs.Pair;
/**
* Strategy to pick reference points by placing them on the axis ends.
*
* This strategy produces n+2 reference points that lie on the edges of the
* surrounding cube.
*
* @author Erich Schubert
*
* @param <V> Vector type
*/
public class AxisBasedReferencePoints<V extends NumberVector<V, ?>> implements ReferencePointsHeuristic<V> {
/**
* Parameter to specify the extra scaling of the space, to allow
* out-of-data-space reference points.
* <p>
* Key: {@code -axisref.scale}
* </p>
*/
public static final OptionID SPACE_SCALE_ID = OptionID.getOrCreateOptionID("axisref.scale", "Scale the data space extension by the given factor.");
/**
* Holds the value of {@link #SPACE_SCALE_ID}.
*/
protected double spacescale;
/**
* Constructor.
*
* @param spacescale
*/
public AxisBasedReferencePoints(double spacescale) {
super();
this.spacescale = spacescale;
}
@Override
public <T extends V> Collection<V> getReferencePoints(Relation<T> db) {
Relation<V> database = DatabaseUtil.relationUglyVectorCast(db);
Pair<V, V> minmax = DatabaseUtil.computeMinMax(database);
V factory = DatabaseUtil.assumeVectorField(database).getFactory();
int dim = DatabaseUtil.dimensionality(db);
// Compute mean and extend from minmax.
double[] mean = new double[dim];
double[] delta = new double[dim];
for(int d = 0; d < dim; d++) {
mean[d] = (minmax.first.doubleValue(d + 1) + minmax.second.doubleValue(d + 1)) / 2;
delta[d] = spacescale * (minmax.second.doubleValue(d + 1) - mean[d]);
}
ArrayList<V> result = new ArrayList<V>(2 + dim);
double[] vec = new double[dim];
// Use min and max
for(int d = 0; d < dim; d++) {
vec[d] = mean[d] - delta[d];
}
result.add(factory.newNumberVector(vec));
for(int d = 0; d < dim; d++) {
vec[d] = mean[d] + delta[d];
}
result.add(factory.newNumberVector(vec));
// Plus axis end points:
for(int i = 0; i < dim; i++) {
for(int d = 0; d < dim; d++) {
if(d != i) {
vec[d] = mean[d] - delta[d];
}
else {
vec[d] = mean[d] + delta[d];
}
}
result.add(factory.newNumberVector(vec));
}
return result;
}
/**
* Parameterization class.
*
* @author Erich Schubert
*
* @apiviz.exclude
*/
public static class Parameterizer<V extends NumberVector<V, ?>> extends AbstractParameterizer {
/**
* Holds the value of {@link #SPACE_SCALE_ID}.
*/
protected double spacescale = 0.0;
@Override
protected void makeOptions(Parameterization config) {
super.makeOptions(config);
DoubleParameter spacescaleP = new DoubleParameter(SPACE_SCALE_ID, new GreaterEqualConstraint(0.0), 1.0);
if(config.grab(spacescaleP)) {
spacescale = spacescaleP.getValue();
}
}
@Override
protected AxisBasedReferencePoints<V> makeInstance() {
return new AxisBasedReferencePoints<V>(spacescale);
}
}
}