// --- BEGIN LICENSE BLOCK ---
/*
* Copyright (c) 2009, Mikio L. Braun
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* * Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following
* disclaimer in the documentation and/or other materials provided
* with the distribution.
*
* * Neither the name of the Technische Universität Berlin nor the
* names of its contributors may be used to endorse or promote
* products derived from this software without specific prior
* written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
// --- END LICENSE BLOCK ---
package org.jblas.util;
import java.util.Random;
import org.jblas.DoubleMatrix;
import org.jblas.FloatMatrix;
/**
* Functions which generate random permutations.
*
* @author Mikio L. Braun
*/
public class Permutations {
/**
* Create a random permutation of the numbers 0, ..., size - 1.
*
* see Algorithm P, D.E. Knuth: The Art of Computer Programming, Vol. 2, p. 145
*/
public static int[] randomPermutation(int size) {
Random r = new Random();
int[] result = new int[size];
for (int j = 0; j < size; j++) {
result[j] = j;
}
for (int j = size - 1; j > 0; j--) {
int k = r.nextInt(j);
int temp = result[j];
result[j] = result[k];
result[k] = temp;
}
return result;
}
/**
* Get a random sample of k out of n elements.
*
* See Algorithm S, D. E. Knuth, The Art of Computer Programming, Vol. 2, p.142.
*/
public static int[] randomSubset(int k, int n) {
assert(0 < k && k <= n);
Random r = new Random();
int t = 0, m = 0;
int[] result = new int[k];
while (m < k) {
double u = r.nextDouble();
if ( (n - t) * u < k - m ) {
result[m] = t;
m++;
}
t++;
}
return result;
}
/**
* Create a permutation matrix from a LAPACK-style 'ipiv' vector.
*
* @param ipiv row i was interchanged with row ipiv[i]
*/
public static DoubleMatrix permutationDoubleMatrixFromPivotIndices(int size, int[] ipiv) {
int n = ipiv.length;
//System.out.printf("size = %d n = %d\n", size, n);
int indices[] = new int[size];
for (int i = 0; i < size; i++)
indices[i] = i;
//for (int i = 0; i < n; i++)
// System.out.printf("ipiv[%d] = %d\n", i, ipiv[i]);
for (int i = 0; i < n; i++) {
int j = ipiv[i] - 1;
int t = indices[i];
indices[i] = indices[j];
indices[j] = t;
}
DoubleMatrix result = new DoubleMatrix(size, size);
for (int i = 0; i < size; i++)
result.put(indices[i], i, 1.0);
return result;
}
/**
* Create a permutation matrix from a LAPACK-style 'ipiv' vector.
*
* @param ipiv row i was interchanged with row ipiv[i]
*/
public static FloatMatrix permutationFloatMatrixFromPivotIndices(int size, int[] ipiv) {
int n = ipiv.length;
//System.out.printf("size = %d n = %d\n", size, n);
int indices[] = new int[size];
for (int i = 0; i < size; i++)
indices[i] = i;
//for (int i = 0; i < n; i++)
// System.out.printf("ipiv[%d] = %d\n", i, ipiv[i]);
for (int i = 0; i < n; i++) {
int j = ipiv[i] - 1;
int t = indices[i];
indices[i] = indices[j];
indices[j] = t;
}
FloatMatrix result = new FloatMatrix(size, size);
for (int i = 0; i < size; i++)
result.put(indices[i], i, 1.0f);
return result;
}
}