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package edu.cmu.tetrad.bayes;

import edu.cmu.tetrad.graph.Graph;
import org.apache.commons.math3.util.FastMath;

/**
 * <p>Provides a static method for finding the Euclidean distance between a pair
 * of BayesIm's.  That is, it computes the square root of the sum of the squares
 * of the differences between corresponding parameters of the two Bayes
 * nets.&gt; 0 <p>The BayesPm's should be equal in the sense of the "equals"
 * method of that class.&gt; 0
 *
 * @author Frank Wimberly
 */
final class BayesImDistanceFunction {

    /**
     * The static distance method's arguments are the two BayesIM's whose
     * BayesPm's are "equal".
     */
    public static double distance(BayesIm firstBn, BayesIm secondBn) {
        if (!firstBn.getBayesPm().equals(secondBn.getBayesPm())) {
            throw new IllegalArgumentException("BayesPms must be equal.");
        }

        Graph graph = firstBn.getBayesPm().getDag();
        int numNodes = graph.getNumNodes();

        double sum = 0.0;

        for (int i = 0; i < numNodes; i++) {
            int numRows = firstBn.getNumRows(i);

            for (int j = 0; j < numRows; j++) {
                int numCols = firstBn.getNumColumns(i);

                for (int k = 0; k < numCols; k++) {
                    double diff = firstBn.getProbability(i, j, k) -
                            secondBn.getProbability(i, j, k);
                    sum += diff * diff;
                }
            }
        }

        return FastMath.sqrt(sum);
    }
}





