add numerical recipes library

lib/nr/cpp/recipes/gaucof.cpp

@@ -0,0 +1,22 @@
+#include <cmath>
+#include "nr.h"
+using namespace std;
+
+void NR::gaucof(Vec_IO_DP &a, Vec_IO_DP &b, const DP amu0, Vec_O_DP &x,
+	Vec_O_DP &w)
+{
+	int i,j;
+
+	int n=a.size();
+	Mat_DP z(n,n);
+	for (i=0;i<n;i++) {
+		if (i != 0) b[i]=sqrt(b[i]);
+		for (j=0;j<n;j++) z[i][j]=DP(i == j);
+	}
+	tqli(a,b,z);
+	eigsrt(a,z);
+	for (i=0;i<n;i++) {
+		x[i]=a[i];
+		w[i]=amu0*z[0][i]*z[0][i];
+	}
+}