平均数、标准差、相关系数

using  System;
using  System.Collections.Generic;
using  System.Text;

namespace  AppMath
{
    public class Maths
    {
        /**//// <summary>
        /// 求出数据平均值,并保留三位小数
        /// </summary>
        /// <param name="Valist">数据集合</param>
        /// <returns></returns>
        public double average(List<double> Valist)
        {
            double sum = 0;
            foreach (double d in Valist)
            {
                sum = sum + d;
            }
            double revl = System.Math.Round(sum / Valist.Count, 3);
            return revl;
        }
        /**//// <summary>
        /// 求数据集合标准差
        /// </summary>
        /// <param name="ValList"></param>
        /// <returns></returns>
        public double stdev(List<double> ValList)
        {
            double avg = average(ValList);
            double sumstdev = 0;
            foreach (double d in ValList)
            {
                sumstdev = sumstdev + (d - avg) * (d - avg);
            }
            double stdeval = System.Math.Sqrt(sumstdev);
            return System.Math.Round(stdeval, 3);
        }
        /**//// <summary>
        /// 相关系数,要求两个集合数量必须相同
        /// </summary>
        /// <param name="array1">数组一</param>
        /// <param name="array2">数组二</param>
        /// <returns></returns>
        public double correl(List<double> array1, List<double> array2)
        {
            //数组一
            double avg1 = average(array1);
            double stdev1 = stdev(array1);
            //数组二
            double avg2 = average(array2);
            double stdev2 = stdev(array2);

            double sum = 0;
            for (int i = 0; i < array1.Count && i < array2.Count; i++)
            {
                sum = sum + ((array1[i] - avg1) / stdev1) * ((array2[i] - avg2) / stdev2);
            }
            return Math.Round(sum, 3);
        }


    }
}