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Graph definitions and algorithms.
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package com.googlecode.blaisemath.graph.metrics;

/*
 * #%L
 * BlaiseGraphTheory
 * --
 * Copyright (C) 2009 - 2019 Elisha Peterson
 * --
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 * #L%
 */

import com.google.common.graph.Graph;
import com.googlecode.blaisemath.graph.GraphUtils;

import java.util.Map;

import static com.google.common.base.Preconditions.checkArgument;

/**
 * Provides a metric describing the decay centrality of a node in a graph.
 * This computation can be slow for large graphs since it uses all nodes in a
 * component. The computation depends on a single decay
 * parameter... a node at distance 1 contributes this parameter, at distance
 * 2 the parameter squared, and so on. As the parameter approaches 1, the
 * metric's value approaches the size of the node's component. As the parameter
 * approaches 0, the metric's value also approaches the parameter times the size
 * of the node's neighborhood.
 *
 * @author Elisha Peterson
 */
public class DecayCentrality extends AbstractGraphNodeMetric {

    /** Decay parameter */
    protected double parameter = 0.5;

    /** Construct with default decay parameter of 0.5 */
    public DecayCentrality() {
        this(0.5);
    }

    /**
     * Construct with specified parameter.
     * @param parameter value of decay parameter
     * @throws IllegalArgumentException if value is outside of the range [0,1]
     */
    public DecayCentrality(double parameter) {
        super("Decay centrality");
        setParameter(parameter);
    }

    @Override
    public String toString() {
        return "DecayCentrality (" + parameter + ")";
    }

    //region PROPERTIES

    /**
     * Get decay parameter.
     * @return value of decay parameter
     */
    public double getParameter() {
        return parameter;
    }

    /**
     * Set new decay parameter.
     * @param newValue new value of decay parameter
     */
    public final void setParameter(double newValue) {
        checkArgument(newValue >= 0 && newValue <= 1, 
                "Parameter for DecayCentrality must be between 0 and 1: " + newValue);
        parameter = newValue;
    }

    //endregion

    @Override
    public  Double apply(Graph graph, N node) {
        Map nvg = GraphUtils.geodesicTree(graph, node);
        return nvg.values().stream().mapToDouble(i -> Math.pow(parameter, i)).sum();
    }
    
}