add numerical recipes library

lib/nr/cpp/recipes/qtrap.cpp

@@ -0,0 +1,21 @@
+#include <cmath>
+#include "nr.h"
+using namespace std;
+
+DP NR::qtrap(DP func(const DP), const DP a, const DP b)
+{
+	const int JMAX=20;
+	const DP EPS=1.0e-10;
+	int j;
+	DP s,olds=0.0;
+
+	for (j=0;j<JMAX;j++) {
+		s=trapzd(func,a,b,j+1);
+		if (j > 5)
+			if (fabs(s-olds) < EPS*fabs(olds) ||
+				(s == 0.0 && olds == 0.0)) return s;
+		olds=s;
+	}
+	nrerror("Too many steps in routine qtrap");
+	return 0.0;
+}