c++ - 用不等式并行化 for 循环 (openmp c++​​)

Question

我尝试并行处理我的这部分代码，但由于使用不等式 != 而出现错误。

 double sum_sin = 0.0, sum_cos = 0.0;
            int count = 0;
    #pragma omp parallel for reduction(+ : count ,sum_sin,sum_cos)
            for (vector<int>::iterator it = box_neighbors[bx[i]].begin(); it != box_neighbors[bx[i]].end(); ++it)
                {
                for (vector<int>::iterator itp = box_particles[*it].begin(); itp != box_particles[*it].end(); ++itp)
                     {
                     if(dist(x[i], y[i], x[*itp], y[*itp], L) < R0_two)
                        {
                        sum_sin+= sin(theta[*itp]);
                        sum_cos+= cos(theta[*itp]);
                        count+=1;  //number of neighbours of i'th particle
                        }
                     }
                }
            sum_sin/= count;
            sum_cos/= count;

如何消除错误？这是错误:

invalid controlling predicate
             for (vector<int>::iterator it = box_neighbors[bx[i]].begin(); it !=

我根据评论修改了代码

           double sum_sin = 0.0, sum_cos = 0.0;
            int count = 0;
            #pragma omp parallel for reduction(+ : count ,sum_sin,sum_cos)
std::vector<int> v; 
for(std::size_t it=0; it<v.size(); ++it) 
            //for (vector<int>::iterator it = box_neighbors[bx[i]].begin(); it != box_neighbors[bx[i]].end(); ++it)
                {
for(std::size_t itp=0; itp<v.size(); ++itp) 
                //for (vector<int>::iterator itp = box_particles[*it].begin(); itp != box_particles[*it].end(); ++itp)
                     {
                     if(dist(x[i], y[i], x[*itp], y[*itp], L) < R0_two)
                        {
                        sum_sin+= sin(theta[*itp]);
                        sum_cos+= cos(theta[*itp]);
                        count+=1;  //number of neighbours of i'th particle
                        }
                     }
                }

但是出现了新的错误:

    error: for statement expected before ‘std’
     std::vector<int> v; 
     ^
 error: invalid type argument of unary ‘*’ (have ‘std::size_t {aka long unsigned int}’)
                          if(dist(x[i], y[i], x[*itp], y[*itp], L) < R0_two)
                                                 ^
  error: invalid type argument of unary ‘*’ (have ‘std::size_t {aka long unsigned int}’)
                          if(dist(x[i], y[i], x[*itp], y[*itp], L) < R0_two)
                                                          ^
    error: invalid type argument of unary ‘*’ (have ‘std::size_t {aka long unsigned int}’)
                             sum_sin+= sin(theta[*itp]);
                                                  ^
   error: invalid type argument of unary ‘*’ (have ‘std::size_t {aka long unsigned int}’)
                             sum_cos+= cos(theta[*itp]);

Answer 1

简单的改变循环条件从

it != box_neighbors[bx[i]].end()

到

it < box_neighbors[bx[i]].end()

从 3.0 版开始，OpenMP 确实支持将随机访问迭代器作为循环变量。但是，您仍然必须遵守不支持 != 的规范循环形式。