定时我的c代码

Question

我在C中编写了一个代码，用于查找两个parabloids之间的数量。虽然在我的时钟上检查时代码运行大约需要7秒，但使用内置时钟功能只需2.6秒。

在并行化后使用openmp运行相同的代码，需要7秒钟。有人可以指出我的时间缺陷吗？

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <time.h>

int main ()
{
    int i, j, k;
    double xmin = 0;
    double xmax = 0.707;
    long Nx = 10000, Ny, n;
    double dx = (xmax - xmin)/(Nx-1);
    double x[Nx];
    double Nelemy[Nx];
    double y, z1, z2;
    double vol1[Nx], vol2[Nx];
    double sum1 = 0, sum2 = 0;
    double start, end, elapsedTime;

    start = clock();

    // Fill in the array containing values at x nodes and number of elements at in y at each node of x
    for (i=0; i<Nx; i++)
    {
        x[i] = 0;
        x[i] = i*dx;
        y = sqrt(1 - 2*x[i]*x[i]);
        n = y/dx;
        Ny = ceil(n) + 1;
        Nelemy[i] = 0;
        Nelemy[i] = Ny;
    }

    // Calculate area for each cell
    double dA = dx*dx;

    // Calculate the value of z for each cell
    for (i=0; i<Nx; i++)
    {
        vol1[i] = 0;
        vol2[i] = 0;
        Ny = Nelemy[i];
        double Y[Ny];
        for (k=0; k<Ny; k++)
        {
            Y[k] = 0;
            Y[k] = k*dx;
        }

        for (j=0; j<Ny; j++)
        {
            z1 = 5 * ( x[i] * x[i] + Y[j] * Y[j]);
            z2 = 6 - 7 *  x[i] * x[i] - Y[j] * Y[j];
            // Calculate the partial volume
            vol1[i] = vol1[i] + dA * z1;
            vol2[i] = vol2[i] + dA * z2;
        }
    }

    // print the contents of vol
    for (i=0; i<Nx; i++)
    {
        sum1 += vol1[i];
        sum2 += vol2[i];
    }
    end = clock();
    elapsedTime = (double)(end - start) / CLOCKS_PER_SEC;

    printf("The enclosed Volume is: %lf\n", (sum2 - sum1));
    printf("The total time taken is: %lf\n", elapsedTime);

    return 0;
}