add numerical recipes library

lib/nr/ansi/recipes/anorm2.c

@@ -0,0 +1,13 @@
+
+#include <math.h>
+
+double anorm2(double **a, int n)
+{
+	int i,j;
+	double sum=0.0;
+
+	for (j=1;j<=n;j++)
+		for (i=1;i<=n;i++)
+			sum += a[i][j]*a[i][j];
+	return sqrt(sum)/n;
+}