add numerical recipes library

lib/nr/cpp/recipes/gamdev.cpp

@@ -0,0 +1,31 @@
+#include <cmath>
+#include "nr.h"
+using namespace std;
+
+DP NR::gamdev(const int ia, int &idum)
+{
+	int j;
+	DP am,e,s,v1,v2,x,y;
+
+	if (ia < 1) nrerror("Error in routine gamdev");
+	if (ia < 6) {
+		x=1.0;
+		for (j=1;j<=ia;j++) x *= ran1(idum);
+		x = -log(x);
+	} else {
+		do {
+			do {
+				do {
+					v1=ran1(idum);
+					v2=2.0*ran1(idum)-1.0;
+				} while (v1*v1+v2*v2 > 1.0);
+				y=v2/v1;
+				am=ia-1;
+				s=sqrt(2.0*am+1.0);
+				x=s*y+am;
+			} while (x <= 0.0);
+			e=(1.0+y*y)*exp(am*log(x/am)-s*y);
+		} while (ran1(idum) > e);
+	}
+	return x;
+}