I have some follow-up info for this thread. The problem still exists,
but here I describe a simple way around it.
My hack for getting around this is to just place the same metal block in
the no-scatterer simulation. I can get away with that because there's a
PML on top.
The no-scatterer run will still behave more or less as free-space
propagation of plane waves because the pml prevents most of the fields
from reaching the reflector. Works great, just a bit non-intuitive in
the sense that your first impulse is to define an empty geometry for the
no-scatterer run.
One might ask why the scatterer runs have metal on the simulation
boundary. I have a back scatterer (metal on the underside of a
scatterer) with a special shape, so Metallic boundaries are
insufficient.
A large gap between this back scatterer and the simulation boundary is
wasted computation, since no fields pass the back scatterer. A small
between the back scatterer and the domain boundary gap leads to some
instabilities (which I can't explain very well). Zero gap wasn't
possible because rounding/gridding errors shift the back scatterer such
that either a small gap exists, or the scatter wraps up across the
lattice boundary, causing the problems I've described.
Maybe it's a useful description for someone :)
Kind Regards,
Matt
On Wed, 10 Jun 2009, matt wrote:
Yes, load-minus flux is from a simulation with exactly the same grid size and
flux-plane size.
The boundary conditions don't change in the scatterer run (k-point is set to
the same vector, and there is no different call to meep-fields-set-boundary).
What does change is that in the scatterer run a block of metal is placed on
top of one of the lattice boundaries.
Best,
Matt
On Wed, 10 Jun 2009, Steven G. Johnson wrote:
On Jun 10, 2009, at 8:33 AM, matt wrote:
When this happens however, the load-minus-flux fails with the following
error:
meep: incorrect dataset size (48000 vs. 96000) in load_dft_hdf5
./test2-refl-flux_noscat_sim_0deg_75res_Hz.h5:ez_dft
load-minus-flux has to be from a simulation with exactly the same grid size
and flux-plane size. Did you change any of these details between your two
calculations? Did you change the boundary conditions?
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