/* Copyright 2009-2016 David Hadka
*
* This file is part of the MOEA Framework.
*
* The MOEA Framework is free software: you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation, either version 3 of the License, or (at your
* option) any later version.
*
* The MOEA Framework 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 Lesser General Public
* License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with the MOEA Framework. If not, see <http://www.gnu.org/licenses/>.
*/
package org.moeaframework.util.sequence;
import org.moeaframework.core.PRNG;
/**
* Generates sequences using Latin hypercube sampling (LHS). Each axis is
* divided into {@code N} stripes and exactly one point may exist in each
* stripe.
* <p>
* References:
* <ol>
* <li>McKay M.D., Beckman, R.J., and Conover W.J. "A Comparison of Three
* Methods for Selecting Values of Input Variables in the Analysis of Output
* from a Computer Code." Technometrics, 21(2):239-245, 1979.
* </ol>
*/
public class LatinHypercube implements Sequence {
/**
* Constructs a Latin hypercube sequence generator.
*/
public LatinHypercube() {
super();
}
@Override
public double[][] generate(int N, int D) {
double[][] result = new double[N][D];
double[] temp = new double[N];
double d = 1.0 / N;
for (int i = 0; i < D; i++) {
for (int j = 0; j < N; j++) {
temp[j] = PRNG.nextDouble(j * d, (j + 1) * d);
}
PRNG.shuffle(temp);
for (int j = 0; j < N; j++) {
result[j][i] = temp[j];
}
}
return result;
}
}