add numerical recipes library

lib/nr/k_and_r/recipes/expdev.c

@@ -0,0 +1,14 @@
+
+#include <math.h>
+
+float expdev(idum)
+long *idum;
+{
+	float ran1();
+	float dum;
+
+	do
+		dum=ran1(idum);
+	while (dum == 0.0);
+	return -log(dum);
+}