add numerical recipes library

lib/nr/cpp/recipes/fredin.cpp

@@ -0,0 +1,12 @@
+#include "nr.h"
+
+DP NR::fredin(const DP x, const DP a, const DP b, Vec_I_DP &t, Vec_I_DP &f,
+	Vec_I_DP &w, DP g(const DP), DP ak(const DP, const DP))
+{
+	int i;
+	DP sum=0.0;
+
+	int n=t.size();
+	for (i=0;i<n;i++) sum += ak(x,t[i])*w[i]*f[i];
+	return g(x)+sum;
+}