add numerical recipes library

lib/nr/cpp/recipes/ttest.cpp

@@ -0,0 +1,17 @@
+#include <cmath>
+#include "nr.h"
+using namespace std;
+
+void NR::ttest(Vec_I_DP &data1, Vec_I_DP &data2, DP &t, DP &prob)
+{
+	DP var1,var2,svar,df,ave1,ave2;
+
+	int n1=data1.size();
+	int n2=data2.size();
+	avevar(data1,ave1,var1);
+	avevar(data2,ave2,var2);
+	df=n1+n2-2;
+	svar=((n1-1)*var1+(n2-1)*var2)/df;
+	t=(ave1-ave2)/sqrt(svar*(1.0/n1+1.0/n2));
+	prob=betai(0.5*df,0.5,df/(df+t*t));
+}