[yt-users] ghost zones and non-periodic boundary conditions

[j s oishi]

Hi all,

I have a question which is kind of a yt question and kind of an enzo
question, so first off, my apologies to the non-enzo users. I have
something that quite clearly appears to be a boundary value problem on
a non-periodic boundary condition. My first method of attack is to
load the (single) root grid data object with its ghost zones:

pf = load(data)
gz = pf.h.grids[0].retrieve_ghost_zones(2,'y-velocity')

However, when I do this on a sample I believe not to have the bug, it
appears that yt is loading periodic boundary conditions in the
non-periodic direction: the first ghost zone on the lower y boundary
is exactly equal to the second-to-top active zone, and the second
lower y ghost zone exactly equals the top active zone. More
concretely,

gz['y-velocity'][:,0,2] always equals gz['y-velocity'][:,-4,2]

and

gz['y-velocity'][:,1,2] always equals gz['y-velocity'][:,-3,2]

This is very clear in the (2D) case at hand, since the velocity field
is a large gradient in the y-direction.

Is it possible that enzo is not outputting its ghost zones, and yt is
simply filling using a periodic method? Or does enzo always output
ghost zones, and this is simply a manifestation of my bug?

I realize this is not a very clear question, but I'm a bit confused myself.

thanks,

j