add numerical recipes library

lib/nr/cpp/recipes/fgauss.cpp

@@ -0,0 +1,21 @@
+#include <cmath>
+#include "nr.h"
+using namespace std;
+
+void NR::fgauss(const DP x, Vec_I_DP &a, DP &y, Vec_O_DP &dyda)
+{
+	int i;
+	DP fac,ex,arg;
+
+	int na=a.size();
+	y=0.0;
+	for (i=0;i<na-1;i+=3) {
+		arg=(x-a[i+1])/a[i+2];
+		ex=exp(-arg*arg);
+		fac=a[i]*ex*2.0*arg;
+		y += a[i]*ex;
+		dyda[i]=ex;
+		dyda[i+1]=fac/a[i+2];
+		dyda[i+2]=fac*arg/a[i+2];
+	}
+}