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) 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 java.util.ArrayList;
import java.util.Collection;
import de.lmu.ifi.dbs.elki.data.NumberVector;
import de.lmu.ifi.dbs.elki.database.ids.DBID;
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.optionhandling.parameters.Flag;
/**
* Star-based strategy to pick reference points.
*
* @author Erich Schubert
*
* @param <V> Object type
*/
public class StarBasedReferencePoints<V extends NumberVector<V, ?>> implements ReferencePointsHeuristic<V> {
/**
* Parameter to specify the grid resolution.
* <p>
* Key: {@code -star.nocenter}
* </p>
*/
public static final OptionID NOCENTER_ID = OptionID.getOrCreateOptionID("star.nocenter", "Do not use the center as extra reference point.");
/**
* Parameter to specify the extra scaling of the space, to allow
* out-of-data-space reference points.
* <p>
* Key: {@code -star.scale}
* </p>
*/
public static final OptionID SCALE_ID = OptionID.getOrCreateOptionID("star.scale", "Scale the reference points by the given factor. This can be used to obtain reference points outside the used data space.");
/**
* Holds the value of {@link #NOCENTER_ID}.
*/
protected boolean nocenter;
/**
* Holds the value of {@link #SCALE_ID}.
*/
protected double scale;
/**
* Constructor.
*
* @param nocenter
* @param scale
*/
public StarBasedReferencePoints(boolean nocenter, double scale) {
super();
this.nocenter = nocenter;
this.scale = scale;
}
@Override
public <T extends V> Collection<V> getReferencePoints(Relation<T> db) {
Relation<V> database = DatabaseUtil.relationUglyVectorCast(db);
V factory = DatabaseUtil.assumeVectorField(database).getFactory();
int dim = DatabaseUtil.dimensionality(db);
// Compute minimum, maximum and centroid
double[] centroid = new double[dim];
double[] min = new double[dim];
double[] max = new double[dim];
for(int d = 0; d < dim; d++) {
centroid[d] = 0;
min[d] = Double.MAX_VALUE;
max[d] = -Double.MAX_VALUE;
}
for(DBID objID : database.iterDBIDs()) {
V obj = database.get(objID);
for(int d = 0; d < dim; d++) {
double val = obj.doubleValue(d + 1);
centroid[d] += val;
min[d] = Math.min(min[d], val);
max[d] = Math.max(max[d], val);
}
}
// finish centroid, scale min, max
for(int d = 0; d < dim; d++) {
centroid[d] = centroid[d] / database.size();
min[d] = (min[d] - centroid[d]) * scale + centroid[d];
max[d] = (max[d] - centroid[d]) * scale + centroid[d];
}
ArrayList<V> result = new ArrayList<V>(2 * dim + 1);
if(!nocenter) {
result.add(factory.newInstance(centroid));
}
// Plus axis end points through centroid
double[] vec = new double[dim];
for(int i = 0; i < dim; i++) {
for(int d = 0; d < dim; d++) {
if(d != i) {
vec[d] = centroid[d];
}
}
vec[i] = min[i];
result.add(factory.newInstance(vec));
vec[i] = max[i];
result.add(factory.newInstance(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 #NOCENTER_ID}.
*/
protected boolean nocenter;
/**
* Holds the value of {@link #SCALE_ID}.
*/
protected double scale;
@Override
protected void makeOptions(Parameterization config) {
super.makeOptions(config);
Flag nocenterF = new Flag(NOCENTER_ID);
if(config.grab(nocenterF)) {
nocenter = nocenterF.getValue();
}
DoubleParameter scaleP = new DoubleParameter(SCALE_ID, new GreaterEqualConstraint(0.0), 1.0);
if(config.grab(scaleP)) {
scale = scaleP.getValue();
}
}
@Override
protected StarBasedReferencePoints<V> makeInstance() {
return new StarBasedReferencePoints<V>(nocenter, scale);
}
}
}