COMBINE documentation:

added the keyword PERIODIC=NO in the example

src/function/Combine.cpp

@@ -48,8 +48,8 @@ its square (as computed from the x,y,z components) and the distance
 again as computed from the square root of the square.
 \verbatim
 DISTANCE LABEL=dist      ATOMS=3,5 COMPONENTS
-COMBINE  LABEL=distance2 ARG=dist.x,dist.y,dist.z POWERS=2,2,2
-COMBINE  LABEL=distance  ARG=distance2 POWERS=0.5
+COMBINE  LABEL=distance2 ARG=dist.x,dist.y,dist.z POWERS=2,2,2 PERIODIC=NO
+COMBINE  LABEL=distance  ARG=distance2 POWERS=0.5 PERIODIC=NO
 PRINT ARG=distance,distance2
 \endverbatim
 (See also \ref PRINT and \ref DISTANCE).