add numerical recipes library

lib/nr/cpp/recipes/fred2.cpp

@@ -0,0 +1,20 @@
+#include "nr.h"
+
+void NR::fred2(const DP a, const DP b, Vec_O_DP &t, Vec_O_DP &f, Vec_O_DP &w,
+	DP g(const DP), DP ak(const DP, const DP))
+{
+	int i,j;
+	DP d;
+
+	int n=t.size();
+	Mat_DP omk(n,n);
+	Vec_INT indx(n);
+	gauleg(a,b,t,w);
+	for (i=0;i<n;i++) {
+		for (j=0;j<n;j++)
+			omk[i][j]=DP(i == j)-ak(t[i],t[j])*w[j];
+		f[i]=g(t[i]);
+	}
+	ludcmp(omk,indx,d);
+	lubksb(omk,indx,f);
+}