计算PageRank的示例分析

本篇文章为大家展示了计算PageRank的示例分析，内容简明扼要并且容易理解，绝对能使你眼前一亮，通过这篇文章的详细介绍希望你能有所收获。

Page Rank就是MapReduce的来源，下文是一个简单的计算PageRank的示例。

import java.text.DecimalFormat;/** * Created by jinsong.sun on 2014/7/15. */public class PageRankCaculator {    public static void main(String[] args) {        double[][] g = calcG(genS(), 0.85);        double[] q = genQ();        int i = 0;        while (i++ < 100000) {            q = calcQ(g, q);            printQString(q);        }    }    public static double[][] genS() {        double[] linkA = {0.00, 0.50, 0.50, 0.00, 0.50};        double[] linkB = {0.25, 0.00, 0.00, 0.00, 0.00};        double[] linkC = {0.25, 0.00, 0.00, 1.00, 0.50};        double[] linkD = {0.25, 0.50, 0.50, 0.00, 0.00};        double[] linkE = {0.25, 0.00, 0.00, 0.00, 0.00};        return new double[][]{linkA, linkB, linkC, linkD, linkE};    }    public static double[] genQ() {        return new double[] {1.00, 1.00, 1.00, 1.00, 1.00};    }    /**     * 计算G矩阵。公式：G = α*S + (1-α)*(1/n)*U     *     * @param s     原始矩阵     * @param alpha 权重     * @return  G矩阵     */    public static double[][] calcG(double[][] s, double alpha) {        int size = 5;        //all one matrix        double[][] u = {{1.00, 1.00, 1.00, 1.00, 1.00}, {1.00, 1.00, 1.00, 1.00, 1.00}                        , {1.00, 1.00, 1.00, 1.00, 1.00}, {1.00, 1.00, 1.00, 1.00, 1.00}                        , {1.00, 1.00, 1.00, 1.00, 1.00}};        //计算a*S        double[][] m1 = new double[size][size];        for (int i = 0; i < s.length; i++) {            for (int j = 0; j < s[i].length; j++) {                m1[i][j] = s[i][j] * alpha;            }        }        //(1-α)*(1/n)*U        double[][] m2 = new double[size][size];        for (int i = 0; i < u.length; i++) {            for (int j = 0; j < u[i].length; j++) {                DecimalFormat df = new DecimalFormat("#.0000");                m2[i][j] = Double.parseDouble(df.format((1.0 - alpha) * (1.0 / size) * u[i][j]));            }        }        //G = α*S + (1-α)*(1/n)*U        double[][] m3 = new double[size][size];        for (int i = 0; i < size; i++) {            for (int j = 0; j < size; j++) {                m3[i][j] = m1[i][j] + m2[i][j];                DecimalFormat df = new DecimalFormat("#.0000");                m3[i][j] = Double.parseDouble(df.format(m3[i][j]));            }        }        return m3;    }    /**     * 计算特征向量。公式：q_next = G * q_curr     *     * @param g     G矩阵     * @param q     特征向量     * @return     */    public static double[] calcQ(double[][] g, double[] q) {        double[] qNext = new double[g.length];        for (int i = 0; i < g.length; i++) {            for (int j = 0; j < g[i].length; j++) {                qNext[i] += g[i][j] * q[j];            }        }        return qNext;    }    public static void printQString(double[] m) {        String s = "{ {:p00}, {:p10}, {:p20}, {:p30}, {:p40} }";        for (int i = 0; i < 5; i++) {            s = s.replace(":p" + i + "0", String.valueOf(m[i]));        }        System.out.println(s);    }}

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