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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) 2014
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.database.relation.RelationUtil;
import de.lmu.ifi.dbs.elki.logging.Logging;
import de.lmu.ifi.dbs.elki.math.MathUtil;
import de.lmu.ifi.dbs.elki.math.linearalgebra.Vector;
import de.lmu.ifi.dbs.elki.utilities.exceptions.AbortException;
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.CommonConstraints;
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.IntParameter;
/**
* Grid-based strategy to pick reference points.
*
* @author Erich Schubert
*/
public class GridBasedReferencePoints implements ReferencePointsHeuristic {
/**
* Class logger.
*/
private static final Logging LOG = Logging.getLogger(GridBasedReferencePoints.class);
/**
* Holds the grid resolution.
*/
protected int gridres;
/**
* Holds the grid scale.
*/
protected double gridscale;
/**
* Constructor.
*
* @param gridres Grid resolution
* @param gridscale Grid scaling
*/
public GridBasedReferencePoints(int gridres, double gridscale) {
super();
this.gridres = gridres;
this.gridscale = gridscale;
}
@Override
public Collection<? extends NumberVector> getReferencePoints(Relation<? extends NumberVector> db) {
double[][] minmax = RelationUtil.computeMinMax(db);
final int dim = minmax[0].length;
// Compute mean from minmax.
double[] mean = new double[dim];
for(int d = 0; d < dim; d++) {
mean[d] = (minmax[0][d] + minmax[1][d]) * .5;
}
if(gridres <= 0) {
LOG.warning("Grid of resolution " + gridres + " will have a single point only.");
ArrayList<Vector> result = new ArrayList<>(1);
result.add(new Vector(mean));
return result;
}
final int grids = gridres + 1;
final int gridpoints = MathUtil.ipowi(grids, dim);
if(gridpoints < 0) {
throw new AbortException("Grids with more than 2^31 are not supported, or meaningful.");
}
if(gridpoints < 0 || gridpoints > db.size()) {
LOG.warning("Grid has " + gridpoints + " points, but you only have " + db.size() + " observations.");
}
ArrayList<Vector> result = new ArrayList<>(gridpoints);
double[] delta = new double[dim];
for(int d = 0; d < dim; d++) {
delta[d] = (minmax[1][d] - minmax[0][d]) / gridres;
}
double halfgrid = gridres * .5;
for(int i = 0; i < gridpoints; i++) {
double[] vec = new double[dim]; // Will be returned!
int acc = i;
for(int d = 0; d < dim; d++) {
int coord = acc % grids;
acc /= grids;
vec[d] = mean[d] + (coord - halfgrid) * delta[d] * gridscale;
}
result.add(new Vector(vec));
}
return result;
}
/**
* Parameterization class.
*
* @author Erich Schubert
*
* @apiviz.exclude
*/
public static class Parameterizer extends AbstractParameterizer {
// TODO: add "grid sampling" option.
/**
* Parameter to specify the grid resolution.
* <p>
* Key: {@code -grid.size}
* </p>
*/
public static final OptionID GRID_ID = new OptionID("grid.size", "The number of partitions in each dimension. Points will be placed on the edges of the grid, except for a grid size of 0, where only the mean is generated as reference point.");
/**
* Parameter to specify the extra scaling of the space, to allow
* out-of-data-space reference points.
* <p>
* Key: {@code -grid.oversize}
* </p>
*/
public static final OptionID GRID_SCALE_ID = new OptionID("grid.scale", "Scale the grid by the given factor. This can be used to obtain reference points outside the used data space.");
/**
* Holds the value of {@link #GRID_ID}.
*/
protected int gridres;
/**
* Holds the value of {@link #GRID_SCALE_ID}.
*/
protected double gridscale;
@Override
protected void makeOptions(Parameterization config) {
super.makeOptions(config);
IntParameter gridP = new IntParameter(GRID_ID, 1);
gridP.addConstraint(CommonConstraints.GREATER_EQUAL_ZERO_INT);
if(config.grab(gridP)) {
gridres = gridP.getValue();
}
DoubleParameter gridscaleP = new DoubleParameter(GRID_SCALE_ID, 1.0);
gridscaleP.addConstraint(CommonConstraints.GREATER_EQUAL_ZERO_DOUBLE);
if(config.grab(gridscaleP)) {
gridscale = gridscaleP.getValue();
}
}
@Override
protected GridBasedReferencePoints makeInstance() {
return new GridBasedReferencePoints(gridres, gridscale);
}
}
}
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