openmp实现PageRank
时间: 2023-07-07 21:26:44 浏览: 98
PageRank是Google搜索引擎排名算法的核心,它是一个迭代算法,其中每个页面的排名取决于其他页面的链接。OpenMP是一种并行编程模型,可以用于加速PageRank算法。
下面是一个简单的OpenMP实现PageRank算法的示例代码:
```c++
#include <omp.h>
#include <stdio.h>
#include <stdlib.h>
#define N 1000
#define EPSILON 0.000001
#define DAMPING_FACTOR 0.85
int main(int argc, char **argv) {
double *page_rank = (double*)malloc(N * sizeof(double));
double *new_page_rank = (double*)malloc(N * sizeof(double));
int *out_degree = (int*)malloc(N * sizeof(int));
int *row_ptr = (int*)malloc((N + 1) * sizeof(int));
int *col_idx = (int*)malloc(N * N * sizeof(int));
double *val = (double*)malloc(N * N * sizeof(double));
// Initialize page_rank, out_degree, row_ptr, col_idx, and val arrays
#pragma omp parallel
{
int tid = omp_get_thread_num();
int num_threads = omp_get_num_threads();
int start_row = tid * (N / num_threads);
int end_row = (tid == num_threads - 1) ? N : (tid + 1) * (N / num_threads);
// Initialize new_page_rank array for this thread
for (int i = start_row; i < end_row; i++) {
new_page_rank[i] = 0.0;
}
while (1) {
// Compute new page ranks for this thread
double delta = 0.0;
for (int i = start_row; i < end_row; i++) {
double sum = 0.0;
for (int j = row_ptr[i]; j < row_ptr[i + 1]; j++) {
sum += val[j] * page_rank[col_idx[j]] / out_degree[col_idx[j]];
}
new_page_rank[i] = DAMPING_FACTOR * sum + (1 - DAMPING_FACTOR) / N;
delta += abs(new_page_rank[i] - page_rank[i]);
}
// Synchronize and update page ranks for all threads
#pragma omp barrier
#pragma omp single
{
double total_delta = 0.0;
for (int i = 0; i < N; i++) {
total_delta += abs(new_page_rank[i] - page_rank[i]);
}
if (total_delta < EPSILON) {
break;
}
double *temp = page_rank;
page_rank = new_page_rank;
new_page_rank = temp;
}
#pragma omp barrier
}
}
free(page_rank);
free(new_page_rank);
free(out_degree);
free(row_ptr);
free(col_idx);
free(val);
return 0;
}
```
在这个示例中,我们使用OpenMP并行化了PageRank算法的迭代过程。每个线程计算一部分页面的新排名,并在每次迭代之后同步更新排名。最后,我们检查总体排名变化量是否小于某个阈值,如果是,则算法结束。
请注意,这只是一个简单的示例,并且没有进行任何错误处理或优化。实际实现中,您需要根据您的具体情况进行更多的调整和优化。