; Material dispersion example, from the Meep tutorial.  Here, we simply; simulate homogenous space filled with a dispersive material, and compute; its modes as a function of wavevector k.  Since omega/c = k/n, we can; extract the dielectric function epsilon(omega) = (ck/omega)^2.(set! geometry-lattice (make lattice (size no-size no-size no-size)))(set-param! resolution 20); We'll use a dispersive material with two polarization terms, just for; illustration.  The first one is a strong resonance at omega=1.1,; which leads to a polaritonic gap in the dispersion relation.  The second; one is a weak resonance at omega=0.5, whose main effect is to add a; small absorption loss around that frequency.(set! default-material      (make dielectric (epsilon 2.25)	    (polarizations 	     (make polarizability	       (omega 1.1) (gamma 1e-5) (delta-epsilon 0.5))	     (make polarizability	       (omega 0.5) (gamma 0.1) (delta-epsilon 2e-5))	     )))(define-param fcen 1.0)(define-param df 2.0)(set! sources (list (make source		      (src (make gaussian-src (frequency fcen) (fwidth df)))		      (component Ez) (center 0 0 0))))(define-param kmin 0.3)(define-param kmax 2.2)(define-param k-interp 99)(define kpts (interpolate k-interp (list (vector3 kmin) (vector3 kmax))))(define all-freqs (run-k-points 200 kpts)) ; a list of lists of frequencies(map (lambda (kx fs)       (map (lambda (f) 	      (print "eps:, " (real-part f) ", " (imag-part f) 		     ", " (sqr (/ kx f)) "\n"))	    fs))     (map vector3-x kpts) all-freqs)