add numerical recipes library

lib/nr/cpp/recipes/gammq.cpp

@@ -0,0 +1,16 @@
+#include "nr.h"
+
+DP NR::gammq(const DP a, const DP x)
+{
+	DP gamser,gammcf,gln;
+
+	if (x < 0.0 || a <= 0.0)
+		nrerror("Invalid arguments in routine gammq");
+	if (x < a+1.0) {
+		gser(gamser,a,x,gln);
+		return 1.0-gamser;
+	} else {
+		gcf(gammcf,a,x,gln);
+		return gammcf;
+	}
+}