REAL FUNCTION ATAN3(A1,A2)
#
#  WORKAROUND FOR ATAN2 BOTH ARGUMENTS = 0
#
   IF (A1==0.0 & A2==0.0)
     ATAN3 = 0.0
   ELSE
     ATAN3 = ATAN2(A1,A2)
   RETURN
   END