Re: [Meep-discuss] strange behavior in output when simulating a gradient index profile

[matt]

Is it possible that you have some field instability?  If you look at the 
absolute field values at the "blip," are they huge?

Are you certain that your material definition is stable?




On Mon, 8 Mar 2010, Aaron Danner wrote:

Dear Friends,

Below is a ctl file where a medium of gradient index is defined 
functionally and a cw point source is defined in it.  At first the 
simulation proceeds normally with waves expanding outwards from the 
dipole.  Suddenly in the simulation waves appear at a totally 
different area in grid and the source is no longer emitting either. 
I have attached a snopshot showing the moment of abrupt change in 
output.  (After this, the source disappears and the new blip just 
stays where it is with no change.) I tried a few different 
frequencies/resolutions and still got this behavior.  For the life of 
me I can't understand what is happening.  I am using the newest 
version of meep.  What could be causing this? There are no error 
messages.  Here is the ctl file:

; Definitions
(define (r p)
        (sqrt (+ (* (vector3-y p) (vector3-y p)) (* (vector3-x p) (vector3-x 
p)) ) )
)

(define (gradientN x)
        (+ 1 (* 0.9935325177161686 x) (* 0.01822651230520182 (expt x 2))
             (* 5.525561315082001 (expt x 3)) (* -6.669270664249898 (expt x 4))
             (* 1.9636753604505492 (expt x 5)) )
)
(define (eps r)
   (if (> r 40.60058497)
        (expt (/ (gradientN (log (/ r 40.60058497))) (/ r 40.60058497)) 2)
        1)
)

; Definition of the medium
(define (f p)
        (make medium
                (epsilon (eps (r p)))
        )
)

;Layout of the simulation
(set! geometry-lattice (make lattice (size 600 600 no-size)))
(set! default-material (make dielectric (epsilon 10)))
(set! geometry (list
        (make sphere (radius 300) (center 0 0)
                (material (make material-function
                        (material-func f)
                ))
       )
))

;Source for the simulation
(set! sources (list
        (make source
                (src (make continuous-src (frequency 0.05)))
                (component Ez)
                (center 0 20)
                (size 0 0)
        )
))

;External boundary conditions
;(set! pml-layers (list (make pml (thickness 50))))

;Grid resolution
(set! resolution 0.5)

;Run parameters
(run-until 400
        (at-beginning output-epsilon)
        (at-every 5 output-efield-z)
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