Naive method for computing minimum distance - slower but needs less memory. - Java java.lang

Java examples for java.lang:Math Geometry Distance

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Description

Naive method for computing minimum distance - slower but needs less memory.

Demo Code

/*//from  ww w.  ja v a2s  . co m
 *  Java Information Dynamics Toolkit (JIDT)
 *  Copyright (C) 2012, Joseph T. Lizier
 *  
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU 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 General Public License for more details.
 *  
 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
//package com.java2s;

public class Main {
    /**
     * Naive method for computing minimum distance - slower but needs less memory.
     * Made public for debugging only. O(d.n^2) speed
     * 
     * @param observations
     * @return
     */
    public static double[] computeMinEuclideanDistancesNaive(
            double[][] observations) {
        int numObservations = observations.length;
        int dimensions = observations[0].length;
        double[] distances = new double[numObservations];
        for (int t = 0; t < numObservations; t++) {
            double minDistance = Double.POSITIVE_INFINITY;
            for (int t2 = 0; t2 < numObservations; t2++) {
                if (t == t2) {
                    continue;
                }
                double thisDistance = 0.0;
                for (int d = 0; (d < dimensions)
                        && (thisDistance < minDistance); d++) {
                    double distanceOnThisVar = (observations[t][d] - observations[t2][d]);
                    thisDistance += distanceOnThisVar * distanceOnThisVar;
                }
                // Now we need to sqrt the distance sum
                thisDistance = Math.sqrt(thisDistance);
                // Now check if this is a lower distance
                if (thisDistance < minDistance) {
                    minDistance = thisDistance;
                }
            }
            distances[t] = minDistance;
        }
        return distances;
    }
}

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