public static float StDev(float[] arrData) //計算標準偏差    {      float xSum = 0F;      float xAvg = 0F;      float sSum = 0F;      float tmpStDev = 0F;      int arrNum = arrData.Length;      for (int i = 0; i < arrNum; i++)      {        xSum += arrData[i];      }      xAvg = xSum / arrNum;      for (int j = 0; j < arrNum; j++)      {        sSum += ((arrData[j] - xAvg) * (arrData[j] - xAvg));      }      tmpStDev = Convert.ToSingle(Math.Sqrt((sSum / (arrNum - 1))).ToString());      return tmpStDev;    }