用于最小，最大，中位数，平均值的OpenMp C ++算法

用于最小，最大，中位数，平均值的OpenMp C ++算法

OpenMP（至少2.0）支持某些简单 *** 作的缩减，但不支持max和min。

在下面的示例中，该

reduction

子句用于求和，而一个

critical

节用于使用线程局部变量无冲突地更新共享变量。

#include <iostream>#include <cmath>int main(){  double sum = 0;  uint64_t ii;  uint64_t maxii = 0;  uint64_t maxii_shared = 0;#pragma omp parallel shared(maxii_shared) private(ii) firstprivate(maxii)  {#pragma omp for reduction(+:sum) nowait    for(ii=0; ii<10000000000; ++ii)      {        sum += std::pow((double)ii, 2.0);        if(ii > maxii) maxii = ii;      }#pragma omp critical     {      if(maxii > maxii_shared) maxii_shared = maxii;    }  }  std::cerr << "Sum: " << sum << " (" << maxii_shared << ")" << std::endl;}

编辑：一个更清洁的实现：

#include <cmath>#include <limits>#include <vector>#include <iostream>#include <algorithm>#include <tr1/random>// sum the elements of vdouble sum(const std::vector<double>& v){  double sum = 0.0;#pragma omp parallel for reduction(+:sum)  for(size_t ii=0; ii< v.size(); ++ii)    {      sum += v[ii];    }  return sum;}// extract the minimum of vdouble min(const std::vector<double>& v){  double shared_min;#pragma omp parallel   {    double min = std::numeric_limits<double>::max();#pragma omp for nowait    for(size_t ii=0; ii<v.size(); ++ii)      {        min = std::min(v[ii], min);      }#pragma omp critical     {      shared_min = std::min(shared_min, min);    }  }  return shared_min;}// generate a random vector and use sum and min functions.int main(){  using namespace std;  using namespace std::tr1;  std::tr1::mt19937 engine(time(0));  std::tr1::uniform_real<> unigen(-1000.0,1000.0);  std::tr1::variate_generator<std::tr1::mt19937,     std::tr1::uniform_real<> >gen(engine, unigen);  std::vector<double> random(1000000);  std::generate(random.begin(), random.end(), gen);  cout << "Sum: " << sum(random) << " Mean:" << sum(random)/random.size()       << " Min:" << min(random) << endl;}