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;
@@ -292,10 +293,13 @@ namespace Misc
 
             for (int i = first; i <= last; i++)
             {
-                if (!double.IsNaN(buf.ElementAt(i)))
+                if ((i >= 0) && (i < buf.Count()))
                 {
-                    sum += (buf.ElementAt(i) - avg) * (buf.ElementAt(i) - avg);
-                    cnt++;
+                    if (!double.IsNaN(buf.ElementAt(i)))
+                    {
+                        sum += (buf.ElementAt(i) - avg) * (buf.ElementAt(i) - avg);
+                        cnt++;
+                    }
                 }
             }
             if (cnt >= 3)