add numerical recipes library

lib/nr/k_and_r/recipes/ftest.c

@@ -0,0 +1,23 @@
+
+void ftest(data1,n1,data2,n2,f,prob)
+float *f,*prob,data1[],data2[];
+unsigned long n1,n2;
+{
+	float betai();
+	void avevar();
+	float var1,var2,ave1,ave2,df1,df2;
+
+	avevar(data1,n1,&ave1,&var1);
+	avevar(data2,n2,&ave2,&var2);
+	if (var1 > var2) {
+		*f=var1/var2;
+		df1=n1-1;
+		df2=n2-1;
+	} else {
+		*f=var2/var1;
+		df1=n2-1;
+		df2=n1-1;
+	}
+	*prob = 2.0*betai(0.5*df2,0.5*df1,df2/(df2+df1*(*f)));
+	if (*prob > 1.0) *prob=2.0-*prob;
+}