方差、标准差

样本中各数据与样本平均数的差的平方和的平均数叫做样本方差；样本方差的算术平方根叫做样本标准差。样本方差和样本标准差都是衡量一个样本波动大小的量，样本方差或样本标准差越大，样本数据的波动就越大

方差       标准差

        /// <summary>
        /// 求方差的算法
        /// </summary>
        /// <param name="qurey">出入操作参数</param>
        /// <returns>返回计算结果</returns>
        public static double FangCha(double[] qurey)
        {
          
            double fangcha = 0;
            double junshu = 0;
            double sum = 0;
            double pinjun = 0;
            if (qurey == null)
            {
                return 0;
            }
            else
            {
                for (int i = 0; i < qurey.Length; i++)
                {
                    junshu += qurey[i];                   
                }

                pinjun = junshu / qurey.Length;

                for (int i = 0; i < qurey.Length; i++)
                {
                    sum += (qurey[i] - pinjun) * (qurey[i] - pinjun);
                   
                }
                fangcha = sum / qurey.Length;
                fangcha = Math.Round(fangcha, 2);
                return fangcha;
            }
        }

/// <summary>
        /// 求标准差算法
        /// </summary>
        /// <param name="qurey">传入操作参数</param>
        /// <returns>返回操作结果</returns>
        public static double BiaoZhunCha(double[] qurey)
        {
            double biaozhuncha = 0;
            double fangcha = 0;
            double junshu = 0;
            double pinjun = 0;
            double sum = 0;
            if (qurey == null)
            {
                return 0;
            }
            else
            {
                for (int i = 0; i < qurey.Length; i++)
                {
                    junshu += qurey[i];
                }

                pinjun = junshu / qurey.Length;

                for (int i = 0; i < qurey.Length; i++)
                {
                    sum += Math.Pow(qurey[i] - pinjun, 2);
                }

                fangcha = sum / qurey.Length;
                biaozhuncha = Math.Sqrt(fangcha);
                biaozhuncha = Math.Round(biaozhuncha, 2);
                return biaozhuncha;
            }
        }