add numerical recipes library

lib/nr/k_and_r/recipes/ttest.c

@@ -0,0 +1,18 @@
+
+#include <math.h>
+
+void ttest(data1,n1,data2,n2,t,prob)
+float *prob,*t,data1[],data2[];
+unsigned long n1,n2;
+{
+	float betai();
+	void avevar();
+	float var1,var2,svar,df,ave1,ave2;
+
+	avevar(data1,n1,&ave1,&var1);
+	avevar(data2,n2,&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)));
+}