add numerical recipes library

lib/nr/cpp/recipes/anorm2.cpp

@@ -0,0 +1,15 @@
+#include <cmath>
+#include "nr.h"
+using namespace std;
+
+DP NR::anorm2(Mat_I_DP &a)
+{
+	int i,j;
+	DP sum=0.0;
+
+	int n=a.nrows();
+	for (j=0;j<n;j++)
+		for (i=0;i<n;i++)
+			sum += a[i][j]*a[i][j];
+	return sqrt(sum)/n;
+}