C++ 与omp支柱平行

我对以下代码有问题：

int *chosen_pts = new int[k];
std::pair<float, int> *dist2 = new std::pair<float, int>[x.n];
// initialize dist2
for (int i = 0; i < x.n; ++i) {
    dist2[i].first = std::numeric_limits<float>::max();
    dist2[i].second = i;
}

// choose the first point randomly
int ndx = 1;
chosen_pts[ndx - 1] = rand() % x.n;
double begin, end;
double elapsed_secs;
while (ndx < k) {
    float sum_distribution = 0.0;
    // look for the point that is furthest from any center
    begin = omp_get_wtime();
    #pragma omp parallel for reduction(+:sum_distribution)
    for (int i = 0; i < x.n; ++i) {

        int example = dist2[i].second;
        float d2 = 0.0, diff;
        for (int j = 0; j < x.d; ++j) {
            diff = x(example,j) - x(chosen_pts[ndx - 1],j);
            d2 += diff * diff;
        }
        if (d2 < dist2[i].first) {
            dist2[i].first = d2;
        }

        sum_distribution += dist2[i].first;

    }

    end = omp_get_wtime() - begin;

    std::cout << "center assigning -- " 
            << ndx << " of " << k << " = " 
            << (float)ndx / k * 100 
            << "% is done. Elasped time: "<< (float)end <<"\n";        

    /**/
    bool unique = true;

    do {
        // choose a random interval according to the new distribution
        float r = sum_distribution * (float)rand() / (float)RAND_MAX;
        float sum_cdf = dist2[0].first;
        int cdf_ndx = 0;
        while (sum_cdf < r) {
            sum_cdf += dist2[++cdf_ndx].first;
        }
        chosen_pts[ndx] = cdf_ndx;

        for (int i = 0; i < ndx; ++i) {
            unique = unique && (chosen_pts[ndx] != chosen_pts[i]);
        }
    } while (! unique);


    ++ndx;
}

int*selected_pts=newint[k]；
std:：pair*dist2=新的std:：pair[x.n]；
//初始化dist2
对于（int i=0；istd：：cout它不是OpenMP并行程序，显然是在串行do while循环中

我看到的一个特殊问题是，当
循环访问
dist2
时，内部
中没有数组边界检查。理论上，边界外访问永远不会发生；但在实践中，它可能会发生-请看下面的原因。因此，首先我将重写
cdf\u ndx
的计算，以确保循环在检查所有元件：

    float sum_cdf = 0;
    int cdf_ndx = 0;
    while (sum_cdf < r && cdf_ndx < x.n ) {
        sum_cdf += dist2[cdf_ndx].first;
        ++cdf_ndx;
    }

循环之后，您需要检查
cdf\u ndx
，否则以新的随机间隔重复。
谢谢！我自己永远也不会明白。浮点算法的问题是未来需要记住的。
    float sum_cdf = 0;
    int cdf_ndx = 0;
    while (sum_cdf < r && cdf_ndx < x.n ) {
        float block_sum = 0;
        int block_end = min(cdf_ndx+10000, x.n); // 10000 is arbitrary selected block size
        for (int i=cdf_ndx; i<block_end; ++i ) {
            block_sum += dist2[i].first;
            if( sum_cdf+block_sum >=r ) {
                block_end = i; // adjust to correctly compute cdf_ndx
                break;
            }
        }
        sum_cdf += block_sum;
        cdf_ndx = block_end;
    }