[Carpet] gf contamination

[Yosef Zlochower]

Hi,

   I am having some difficulty when evolving my code with carpet.  I am
attempting to evolve my code with prolongation in space only.  To
better understand the problem I set up my code so that the RHS were
all filled with 1.0e4 prior to calculating them. My code then fills in
the RHS for all points on the grid except those on the three
gridplanes closest to the boundary (i.e. for (i=3; i<cctk_lsh[0]-3;
i++) etc ). In MoL_PostStep I first synchronize all the evolved fields
(but not the RHS) and then alter the values of \tilde g_{ij} and
\tilde A_{ij} so that the algebraic constraints are enforced. I am
working on a problem where gxy = 0. However, I found that after 1
timestep the value of gxy 1 point in from the buffer zones is
non-zero, and grows when I increase the initial value of the RHS to
1.0e5. So it looks like some junk from the buffer zones has leaked
into the evolved fields.

Here is the relevant segment of my parfile please note that my code
only needs 3 ghostzones but I choose 4. I also set
num_integrator_substeps = 4 even though 3 would be sufficient.
(setting it back to 3 does not remove the problem)


driver::ghost_size = 4
mol::ode_method                        = "RK3"
driver::global_nx                       = 81 #51 #227 #259
driver::global_ny                       = 81 #51 #227 #259
driver::global_nz                       = 81 #51 #116 #132
grid::dxyz                              = .25
grid::domain                            = "full"

time::dtfac                             = 0.125
#Carpet::prolongation_order_space   = 7
Carpet::prolongation_order_space   = 1
Carpet::prolongation_order_time    = 0
Carpet::max_refinement_levels      = 3 #5
#Carpet::buffer_width               = 0
Carpet::time_refinement_factors = "[1,1,1]"
Carpet::num_integrator_substeps = 4
Carpet::use_outer_buffer_zones = "yes"
#Carpet::init_each_timelevel = "yes"

CarpetRegrid::refinement_levels    = 3 #5
CarpetRegrid::regrid_every         = 0
CarpetRegrid::refined_regions = "centre"

Is there something obviously wrong in the parfile?

I examined gxy on the y axis and found that after the first time step
gxy on level 0 is zero except at y=+-5 and +-2.5 On level 1 gxy has
the same behavior but is also non-zero at the points directly above
and below +-5. On the finest level gxy is non-zero on +-2.5 and +-
2.4375.

Yosef