add numerical recipes library

lib/nr/k_and_r/recipes/erfcc.c

@@ -0,0 +1,15 @@
+
+#include <math.h>
+
+float erfcc(x)
+float x;
+{
+	float t,z,ans;
+
+	z=fabs(x);
+	t=1.0/(1.0+0.5*z);
+	ans=t*exp(-z*z-1.26551223+t*(1.00002368+t*(0.37409196+t*(0.09678418+
+		t*(-0.18628806+t*(0.27886807+t*(-1.13520398+t*(1.48851587+
+		t*(-0.82215223+t*0.17087277)))))))));
+	return x >= 0.0 ? ans : 2.0-ans;
+}