遍历数组一次求得数组的平均数、标准差、方差

static Tuple<double,double,double> ComputeVariance2(double[] a)
{
    double variance = 0;    //方差
    double sum = 0;         //总和
    double sum2 = 0;        //平方和
    int len = a.Length;
    for (int i = 0; i < len; i++)
    {
        sum += a[i];
        sum2 += a[i] * a[i];
    }
    variance = sum2 / len - (sum / len) * (sum / len);
    //                  平均数   标准差               方差
    return Tuple.Create(sum/len, Math.Sqrt(variance), variance);
}