--- ray/src/common/linregr.c	1991/11/12 16:55:46	2.1
+++ ray/src/common/linregr.c	1993/03/05 15:14:02	2.2
@@ -8,6 +8,8 @@ static char SCCSid[] = "$SunId$ LBL";
  * Basic linear regression calculation.
  */
 
+#include <math.h>
+
 #include "linregr.h"