minor modifications for interpolation and mythe data structure

slsDetectorCalibration/Stat.h

@@ -0,0 +1,45 @@
+class Stat
+  {
+  public:
+    
+  Stat() : n(0), m(0.), m2(0.) {}
+    
+    void Clear()
+    {
+      n = 0;
+      m=0;
+      m2=0;
+    }
+    
+        void Push(double x)
+        {
+	  
+	  m+=x;
+	  m2+=x*x;
+            n++;
+        }
+
+        int NumDataValues() const
+        {
+            return n;
+        }
+
+        double Mean() const
+        {
+            return (n > 0) ? m/n : 0.0;
+        }
+
+        double Variance() const
+        {
+	  return ( (n >0 ) ? (m2/n-m*m/(n*n)) : 0.0 );
+        }
+
+        double StandardDeviation() const
+        {
+            return sqrt( Variance() );
+        }
+
+    private:
+        int n;
+        double m, m2;
+    };