--- ray/src/px/psum.c	1991/12/19 14:52:02	2.2
+++ ray/src/px/psum.c	1993/06/04 14:47:18	2.3
@@ -12,6 +12,8 @@ static char SCCSid[] = "$SunId$ LBL";
 
 #include  <stdio.h>
 
+#include  <math.h>
+
 #include  "color.h"