修复 sigma函数没有检测数据范围

Project.FLY.Misc/MISC/MyMath.cs

@@ -283,6 +283,7 @@ namespace Misc
         /// <returns></returns>
         public static double Sigma(IEnumerable<double> buf, int first, int last)
         {
+            
             double avg = Avg(buf, first, last);
             if (double.IsNaN(avg))
                 return double.NaN;
@@ -291,6 +292,8 @@ namespace Misc
             int cnt = 0;
 
             for (int i = first; i <= last; i++)
+            {
+                if ((i >= 0) && (i < buf.Count()))
                 {
                     if (!double.IsNaN(buf.ElementAt(i)))
                     {
@@ -298,6 +301,7 @@ namespace Misc
                         cnt++;
                     }
                 }
+            }
             if (cnt >= 3)
                 return (Math.Sqrt(sum / (cnt - 1)));
             else