生成正态分布(高斯分布)的随机数

double generateGaussianNoise(double mu, double sigma)
{
    const double epsilon = std::numeric_limits<double>::min();
    const double two_pi = 2.0*3.14159265358979323846;

    static double z0, z1;
    static bool generate;
    generate = !generate;

    if (!generate)
       return z1 * sigma + mu;

    double u1, u2;
    do
     {
       u1 = rand() * (1.0 / RAND_MAX);
       u2 = rand() * (1.0 / RAND_MAX);
     }
    while ( u1 <= epsilon );

    z0 = sqrt(-2.0 * log(u1)) * cos(two_pi * u2);
    z1 = sqrt(-2.0 * log(u1)) * sin(two_pi * u2);
    return z0 * sigma + mu;
}

int Generate_demand(double mu,double sigma)
{
    return (int)(generateGaussianNoise(mu,sigma)+0.5);
}