stats.MessageLengthFactorialComputer.java Source code

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Here is the source code for stats.MessageLengthFactorialComputer.java

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/*******************************************************************************
 * Copyright (C) 2015 Francois Petitjean
 * 
 * This file is part of Chordalysis.
 * 
 * Chordalysis 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, version 3 of the License.
 * 
 * Chordalysis 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 Chordalysis.  If not, see <http://www.gnu.org/licenses/>.
 ******************************************************************************/
package stats;

import java.util.BitSet;
import java.util.HashMap;

import lattice.Lattice;
import lattice.LatticeNode;

import org.apache.commons.math3.util.FastMath;

/**
 * This class aims at computing the length of the message transmitting the data
 * associated with a clique of variables, given that the frequencies have know
 * by the receiver. See paper
 * "A statistically efficient and scalable method for log-linear analysis of high-dimensional data, ICDM 2014"
 * 
 * @see http://www.tiny-clues.eu/Research/
 * @author Dr Francois Petitjean
 */
public class MessageLengthFactorialComputer {
    public long nbCellsEverParsed;
    HashMap<BitSet, Double> lookup;
    double[] logs;
    double[] logFactorials;

    Lattice lattice;
    int nbInstances;
    double lnN;

    public MessageLengthFactorialComputer(int nbInstances, Lattice lattice) {
        this.lookup = new HashMap<BitSet, Double>();
        this.lattice = lattice;
        this.nbInstances = nbInstances;

        int nbFactorials = this.nbInstances + 2;
        int nbVariables = lattice.getNbVariables();
        int nbMaxEdges = nbVariables * (nbVariables - 1) / 2;
        if (nbMaxEdges + 2 > nbFactorials) {
            nbFactorials = nbMaxEdges + 3;
        }

        this.logs = new double[nbFactorials];
        for (int i = 0; i < logs.length; i++) {
            logs[i] = FastMath.log(i);
        }
        lnN = logs[nbInstances];

        this.logFactorials = new double[nbFactorials];
        logFactorials[0] = logs[1];
        logFactorials[1] = logs[1];
        for (int i = 2; i < logFactorials.length; i++) {
            logFactorials[i] = logFactorials[i - 1] + logs[i];
        }
        nbCellsEverParsed = 0;

        lookup.put(new BitSet(lattice.getNbVariables()), 0.0);

    }

    public double computeLengthData(BitSet clique) {
        Double computedLength = lookup.get(clique);
        if (computedLength != null) {
            // System.out.println("sending "+clique+" costs "+computedLength+" nits");
            return computedLength;
        }

        LatticeNode node = lattice.getNode(clique);
        int nbCells = node.getNbCells();
        nbCellsEverParsed += nbCells;

        double length = 0.0;
        // stating the position in data
        length += logFactorials[nbInstances];
        for (int i = 0; i < nbCells; i++) {
            int O = node.getMatrixCell(i);
            length -= logFactorials[O];
        }
        lookup.put(clique, length);
        // System.out.println("sending "+clique+" costs "+length+" nits");
        return length;
    }

    public int getNbInstances() {
        return nbInstances;
    }

    public int getNbVariables() {
        return lattice.getNbVariables();
    }

    public double[] getLogFactorials() {
        return logFactorials;
    }

    public double[] getLogs() {
        return logs;
    }

    public final double getLogFromTable(int i) {
        return logs[i];
    }

}