add numerical recipes library

lib/nr/cpp/recipes/sphbes.cpp

@@ -0,0 +1,18 @@
+#include <cmath>
+#include "nr.h"
+using namespace std;
+
+void NR::sphbes(const int n, const DP x, DP &sj, DP &sy, DP &sjp, DP &syp)
+{
+	const DP RTPIO2=1.253314137315500251;
+	DP factor,order,rj,rjp,ry,ryp;
+
+	if (n < 0 || x <= 0.0) nrerror("bad arguments in sphbes");
+	order=n+0.5;
+	bessjy(x,order,rj,ry,rjp,ryp);
+	factor=RTPIO2/sqrt(x);
+	sj=factor*rj;
+	sy=factor*ry;
+	sjp=factor*rjp-sj/(2.0*x);
+	syp=factor*ryp-sy/(2.0*x);
+}