PageRank算法c++实现

首先用邻接矩阵A表示从页面j到页面i的概率，然后根据公式生成转移概率矩阵

M=（1-d）*Q+d*A 常量矩阵Q=(qi,j),qi,j=1/n

给定点击概率d，等级值初始向量R0，迭代终止条件e；

计算Ri+1=M*Ri；

ei=|Ri+1-Ri|，当ei<=e时输出Ri+1作为最终等级值向量。

#include "fstream"
#include "sstream"
#include <iostream>
#include <set>
#include <vector>

using namespace std;

int getNum()
{
    set<int> N;
    ifstream is("a.txt");
    int u, v;
    while (is >> u >> v)
    {
        N.insert(u);
        N.insert(v);
    }
    return N.size();
}

void getPage(vector<vector<int>>& page)     //&
{
    ifstream is("a.txt");
    int u, v;
    while(is>>u>>v)
    { 
        page[u].push_back(v);
    }
}

void PageRank(vector<vector<int>>&page,int N,double d,double e,int maxIterations)
{
    //得到M
    vector<vector<double>> M(N,vector<double>(N,0.0));
   
    for (int i = 0; i < N; i++)
    {
        if (page[i].size() > 0)
        {
            for (int j : page[i])
            {
                M[j][i]++;           //0/1
                
            }
            for (int j=0;j<N;j++)
            {
                M[j][i] /= page[i].size();
            }
        }
        else
        {
            for (int j : page[i])
            {
                M[j][i] = 0;
            }
        }
    }
    for (int i = 0; i < N; i++)
    {
        for (int j = 0; j < N; j++)
        {
            //cout << M[i][j]<<" ";             //正确
            M[i][j] = d * M[i][j] + (1 - d) * (1.0 / N);
            //cout << M[i][j] << " ";
        }
    }

    vector<double> pagerank(N, 1.0);
    while (maxIterations)
    {
        vector<double> newpagerank(N, 0.0);
        double dif=0.0;
        for (int i = 0; i < N; i++)
        {
            for (int j = 0; j < N; j++)
            {
                newpagerank[i] += M[i][j] * pagerank[j];
            }
             dif+= abs(pagerank[i]-newpagerank[i]);
        }
        //cout << dif << endl;
        pagerank = newpagerank;
        if (dif < e)
        {
            //cout << maxIterations<<endl;
            break;
        }
        maxIterations--;
    }
    cout << "等级值分别为：" << endl;
    for (int i = 0; i < N; i++)
    {
        cout << pagerank[i]<<endl;
    }
}

int main()
{
    int num = getNum();
    vector<vector<int>> page(num);
    getPage(page);
    double d = 0.85;
    double e = 0.1;
    int maxIterations = 100;
    PageRank(page, num, d, e, maxIterations);

}

数据

0 1
0 2
0 3
1 0
1 2
2 3
3 0
3 1

结果

PageRank算法c++实现

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