add numerical recipes library

lib/nr/ansi/recipes/ttest.c

@@ -0,0 +1,17 @@
+
+#include <math.h>
+
+void ttest(float data1[], unsigned long n1, float data2[], unsigned long n2,
+	float *t, float *prob)
+{
+	void avevar(float data[], unsigned long n, float *ave, float *var);
+	float betai(float a, float b, float x);
+	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)));
+}