PageRank算法原理及实现

 1 typedef unsigned char BYTE;
 2 class CPageRank
 3 {
 4 public:
 5     CPageRank(int nWebNum = 5, bool bLoadFromFile = false);
 6    ~CPageRank();
 7 
 8    int Process();
 9    float *GetWeight();
10 
11 private:
12    void InitGraph(bool bLoadFromFile = false);
13    void GenerateP();
14    BYTE *m_pu8Relation; //节点关系 i行j列表示j是否指向i
15    float *m_pf32P; //转移矩阵
16    
17    //缓存
18    float *m_pf32Weight0;
19    float *m_pf32Weight1;
20    int *m_pl32Out;
21    int m_nNum;
22    float m_f32DampFactor; //阻尼系数
23 
24    int m_nMaxIterTime;
25    float m_f32IterErr;
26    float *m_pf32OutWeight;//输出的最终权重
27 };

 1 CPageRank::CPageRank(int nWebNum, bool bLoadFromFile)
 2 {
 3      m_f32DampFactor = 0.85;
 4      m_nMaxIterTime = 1000;
 5      m_f32IterErr = 1e-6;
 6  
 7      m_nNum = nWebNum;
 8      m_pu8Relation = new BYTE[m_nNum * m_nNum];
 9      m_pf32P = new float[m_nNum * m_nNum];
10      m_pf32Weight0 = new float[m_nNum];
11      m_pf32Weight1 = new float[m_nNum];
12      m_pl32Out = new int[m_nNum];//每个节点指向的节点数
13  
14      InitGraph(bLoadFromFile);  
15 }

1 CPageRank::~CPageRank()
2  {
3      delete []m_pl32Out;
4      delete []m_pf32P;
5      delete []m_pf32Weight0;
6      delete []m_pf32Weight1;
7      delete []m_pu8Relation;
8  }

 1 void CPageRank::InitGraph(bool bLoadFromFile)
 2  {
 3      FILE *pf = NULL;
 4      if(bLoadFromFile)
 5      {
 6          pf = fopen("map.dat", "rb");
 7          if(pf)
 8          {
 9              fread(m_pu8Relation, sizeof(BYTE), m_nNum * m_nNum, pf);
10              fclose(pf);
11              return;
12          }
13      }
14  
15      //建立随机的节点指向图
16      int i, j;
17      srand((unsigned)time(NULL));
18      for(i = 0; i < m_nNum; i++)
19      {
20          //指向第i个的节点
21          for(j = 0; j < m_nNum; j++)
22          {
23              m_pu8Relation[i * m_nNum + j] = rand() & 1;
24          }
25          //自己不指向自己
26          m_pu8Relation[i * m_nNum + i] = 0;
27      }
28  
29      pf = fopen("map.dat", "wb");
30      if(pf)
31      {
32          fwrite(m_pu8Relation, sizeof(BYTE), m_nNum * m_nNum, pf);
33          fclose(pf);
34      }         
35  }

 1 void CPageRank::GenerateP()
 2  {
 3      int i,j;
 4      float *pf32P = NULL;
 5      BYTE *pu8Relation = NULL;
 6  
 7      //统计流入流出每个节点数
 8      memset(m_pl32Out, 0, m_nNum * sizeof(int));
 9      pu8Relation = m_pu8Relation;
10      for(i = 0; i < m_nNum; i++)
11      {
12          for(j = 0; j < m_nNum; j++)
13          {
14              m_pl32Out[j] += *pu8Relation;
15              pu8Relation++;
16          }
17      }
18  
19      //生成转移矩阵,每个节点的权重平均流出
20      pu8Relation = m_pu8Relation;
21      pf32P = m_pf32P;
22      for(i = 0; i < m_nNum; i++)
23      {
24          for(j = 0; j < m_nNum; j++)
25          {
26              if(m_pl32Out[j] > 0)
27              {
28                  *pf32P = *pu8Relation * 1.0f / m_pl32Out[j];
29              }
30              else
31              {
32                  *pf32P = 0.0f;
33              }
34              pu8Relation++;
35              pf32P++;
36          }
37      }
38  
39      //考虑阻尼系数，修正转移矩阵
40      pf32P = m_pf32P;
41      for(i = 0; i < m_nNum; i++)
42      {
43          for(j = 0; j < m_nNum; j++)
44          {
45              *pf32P = *pf32P * m_f32DampFactor;
46              pf32P++;
47          }
48      }
49  }

 1 int CPageRank::Process()
 2  {
 3      int i,j,k,t;
 4      float f32MaxErr = 0.0f;
 5      float *pf32Org = m_pf32Weight0;
 6      float *pf32New = m_pf32Weight1;
 7      float f32MinWeight = (1 - m_f32DampFactor) / m_nNum;
 8  
 9      //设置初始值，全1
10      for(i = 0; i < m_nNum; i++)
11      {
12          pf32Org[i] = 1.0f / m_nNum;//rand() * 2.0f / RAND_MAX;
13      }
14  
15     //生成P矩阵
16      GenerateP();
17  
18      //迭代
19      for(t = 0; t < m_nMaxIterTime; t++)
20      {
21          //开始迭代
22          f32MaxErr = 0.0f;
23          for(i = 0; i < m_nNum; i++)
24          {
25              pf32New[i] = f32MinWeight;
26              int l32Off = i * m_nNum;
27              for(j = 0; j < m_nNum; j++)
28              {
29                  pf32New[i] += m_pf32P[l32Off + j] * pf32Org[j];
30              }
31  
32              float f32Err = fabs(pf32New[i] - pf32Org[i]);
33              if(f32Err > f32MaxErr)
34              {
35                  f32MaxErr = f32Err;
36              }
37          }
38 
39          //迭代误差足够小，停止
40          if(f32MaxErr < m_f32IterErr)
41          {
42              break;
43          }
44  
45          //交换2次迭代结果
46          float *pf32Temp = pf32Org;
47          pf32Org = pf32New;
48          pf32New = pf32Temp;
49      }
50  
51      //迭代结果存在pf32New中
52      m_pf32OutWeight = pf32New;
53      return t;
54  }

1  float * CPageRank::GetWeight()
2  {
3      return m_pf32OutWeight;
4  }