GraphEliminationTest.java

/*******************************************************************************
 * Copyright (c) 2013 Michael Kutschke.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     Michael Kutschke - initial API and implementation
 ******************************************************************************/
package org.eclipse.recommenders.jayes.util.triangulation;

import static org.eclipse.recommenders.jayes.util.GraphTest.createTestGraph;
import static org.hamcrest.CoreMatchers.hasItems;
import static org.hamcrest.core.Is.is;
import static org.junit.Assert.*;

import java.util.Arrays;
import java.util.Iterator;
import java.util.List;

import org.eclipse.recommenders.jayes.util.Graph;
import org.junit.Test;

public class GraphEliminationTest {

    /**
     * <pre>
     * 1-3
     * |/
     * 0--2
     *
     * where 3 has higher weight just for predictability
     * </pre>
     */
    @Test
    public void testMinFillIn() {
        Graph graph = createTestGraph();

        double[] weights = new double[] { 0d, 0d, 1d, 0d };

        GraphElimination minFillIn = new GraphElimination(graph, weights, new MinFillIn());
        Iterator<List<Integer>> it = minFillIn.iterator();
        List<Integer> first = it.next();
        // eliminate 1
        assertThat(first, hasItems(0, 1, 3));
        assertThat(first.size(), is(3));
        List<Integer> second = it.next();
        // eliminate 3
        assertThat(second, hasItems(0, 3));
        assertThat(second.size(), is(2));
        List<Integer> third = it.next();
        // eliminate 0 - here because eliminating it before would cause fillIn
        assertThat(third, hasItems(0, 2));
        assertThat(third.size(), is(2));
        List<Integer> fourth = it.next();
        // eliminate 2 - here because it has higher weight
        assertThat(fourth, is(Arrays.asList(2)));

        assertFalse(it.hasNext()); // sanity check
    }

    @Test
    public void testQuotientGraph() {
        Graph graph = createTestGraph();
        QuotientGraph q = new QuotientGraph(graph);

        // check that initially everything is as we expect
        assertThat(q.getNeighbors(0), hasItems(1, 2, 3));
        assertThat(q.getNeighbors(0).size(), is(3));
        assertThat(q.getNeighbors(1), hasItems(0, 3));
        assertThat(q.getNeighbors(1).size(), is(2));
        assertThat(q.getNeighbors(2), hasItems(0));
        assertThat(q.getNeighbors(2).size(), is(1));
        assertThat(q.getNeighbors(3), hasItems(0, 1));
        assertThat(q.getNeighbors(3).size(), is(2));

        q.eliminate(1); // this only removes node 1

        assertThat(q.getNeighbors(0), hasItems(2, 3));
        assertThat(q.getNeighbors(0).size(), is(2));
        assertThat(q.getNeighbors(1).size(), is(0));
        assertThat(q.getNeighbors(2), hasItems(0));
        assertThat(q.getNeighbors(2).size(), is(1));
        assertThat(q.getNeighbors(3), hasItems(0));
        assertThat(q.getNeighbors(3).size(), is(1));

        q.eliminate(0); // node 2 and 3 get connected

        assertThat(q.getNeighbors(0).size(), is(0));
        assertThat(q.getNeighbors(1).size(), is(0));
        assertThat(q.getNeighbors(2), hasItems(3));
        assertThat(q.getNeighbors(2).size(), is(1));
        assertThat(q.getNeighbors(3), hasItems(2));
        assertThat(q.getNeighbors(3).size(), is(1));
    }

}