Hi JP, Periodicity can only be induced on a single "sub box" ... So you'll need to rethink your approach a bit. (I tried to look at your example, but am guessing that is simpler than your true target.) I can see that there are some configurations that definitely wouldn't work in genbox. Here is one idea: Set the "P " bcs to " " (3 blanks). Then, just run the output through pretex (text-based prenek ) and when you get to the BC menu just SET ENTIRE LEVEL AUTO-PERIODIC. This should just work... (beware, there are some tricky issues with periodicity when using millions of elements -- it's a workflow issue that we're trying to clean up). Paul ________________________________ From: [email protected] [[email protected]] on behalf of [email protected] [[email protected]] Sent: Sunday, December 04, 2016 5:15 PM To: nek5000-users Subject: [Nek5000-users] Genbox periodic simple case Dear Users, I have used genbox for ages but now I need to split a channel in the x direction and cannot make genmap recognize the periodic boundary conditions. Can a periodic boundary condition be separated by a box? I need periodic boundary conditions in x and z. This is my .box: ------------------------- parameters.rea -3 1 # Left box Box1 -10 -10 -10 0.000 2.000 1.00 0.000 2.000 1.00 0.000 2.000 1.00 P ,E ,W ,W ,P ,P bc's # Right box Box2 -10 -10 -10 2.000 4.000 1.00 0.000 2.000 1.00 0.000 2.000 1.00 E ,P ,W ,W ,P ,P bc's -------------------------- I thought it should be really simple but I cannot get it to work... any help/insight? Regards, JP