On Jul 30, 2008, at 9:20 PM, Jefferson Thomas wrote: > What you are saying is really very helpful. In fact I had no idea I > have to supply the symmetric > source. I will try it right now and see how it goes.
See: http://ab-initio.mit.edu/wiki/index.php/Exploiting_symmetry_in_Meep If you don't supply a symmetric source, in practice Meep will symmetrize it for you, although it is better to have a symmetric source so that you get the same results with and without symmetry (this makes things easier to debug). However, the fact that you were specifying an Ex source at y=0 but also specifying odd symmetry around y=0 indicates that you either have a typo or were fundamentally misunderstanding the relationship between symmetry and fields -- either way, it is very important to correct. > On the other hand I dont understand the thing with the symmetric eps. > Although I dont know how meep works internally with the symmetries I > have been checking already many times > what requests it sends to the eps function. From what I have found > out, if there is any symmetry meep > asks the eps function only about one relevant half of the volume. Yes, it only evaluates the eps function in *about* one half of the volume. However, it evaluates eps for about one pixel beyond the mirror plane too, and if your epsilon function isn't symmetric then terrible things can happen. > So lets say I declare the calculation volume : > volume v = vol3d(10,10,10, resolution); > And then I specify the X symmetry : > structure s(v, eps, pml(1.0), meep::mirror(meep::X, v)); > Then all the vector requests that come to the eps function have x > coordinate > between 0 and 5 (or precisely between -0.xx and 5.xx but that is just > a minor issue). The 5.xx is not a minor issue. It's exactly this tiny fraction beyond the midpoint that is causing your problem since your eps function is not symmetrical (as proved by the fact that the divergence disappears when I symmetrized your eps function). Hence the divergences you observe starting at the boundary, because the boundary conditions are internally inconsistent. Steven _______________________________________________ meep-discuss mailing list [email protected] http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss
