> On May 22, 2019, at 4:49 AM, ei ru <37zi...@gmail.com> wrote:
> Thank you for the response.
> In my simulation, the boundary between negative- and positive-index materials
> does not exist, because everywhere is negative-index material. What do you
> refer as positive-index material?
> Thank you very much.
If everywhere in your simulation is negative index, then in principle there is
no problem with simulating it in FDTD, but you are correct that in this case
our PML would not work because it has the wrong sign. Currently, the only way
to change the PML sign would be to edit the source code — for simulations of
everywhere-negative index material, flip the sign of "prefac" in structure.cpp:
https://github.com/NanoComp/meep/blob/32d4e4de4695fbb5e0ed4927d36eeb88881bd44a/src/structure.cpp#L651
<https://github.com/NanoComp/meep/blob/32d4e4de4695fbb5e0ed4927d36eeb88881bd44a/src/structure.cpp#L651>
That being said, I should comment that a simulation that has a negative index
everywhere is probably not so interesting. It is exactly equivalent to a
simulation with a positive index everywhere if you apply the coordinate
inversion (x,y,z) -> (-x,-y,-z), as described in these notes:
https://math.mit.edu/~stevenj/18.369/coordinate-transform.pdf
<https://math.mit.edu/~stevenj/18.369/coordinate-transform.pdf>
so you won't learn anything that you wouldn't from the equivalent
positive-index simulation._______________________________________________
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