public static float StDev(float[] arrData) //计算标准偏差
    {
      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;
    }