add numerical recipes library

lib/nr/cpp/recipes/poidev.cpp

@@ -0,0 +1,39 @@
+#include <cmath>
+#include "nr.h"
+using namespace std;
+
+DP NR::poidev(const DP xm, int &idum)
+{
+	const DP PI=3.141592653589793238;
+	static DP sq,alxm,g,oldm=(-1.0);
+	DP em,t,y;
+
+	if (xm < 12.0) {
+		if (xm != oldm) {
+			oldm=xm;
+			g=exp(-xm);
+		}
+		em = -1;
+		t=1.0;
+		do {
+			++em;
+			t *= ran1(idum);
+		} while (t > g);
+	} else {
+		if (xm != oldm) {
+			oldm=xm;
+			sq=sqrt(2.0*xm);
+			alxm=log(xm);
+			g=xm*alxm-gammln(xm+1.0);
+		}
+		do {
+			do {
+				y=tan(PI*ran1(idum));
+				em=sq*y+xm;
+			} while (em < 0.0);
+				em=floor(em);
+				t=0.9*(1.0+y*y)*exp(em*alxm-gammln(em+1.0)-g);
+		} while (ran1(idum) > t);
+	}
+	return em;
+}