; Compute the band structure for a Bragg mirror consisting of a; sinusoidally-varying dielectric index.; The index will vary sinusoidally between index-min and index-max:(define-param index-min 1)(define-param index-max 3)(define pi (* 4 (atan 1))) ; 3.14159...; Define a function of position p (in the lattice basis) that returns; the material at that position.  In this case, we use the function:;        index-min + 0.5 * (index-max - index-min);                        * (1 + cos(2*pi*x)); This is periodic, and also has inversion symmetry.(define (eps-func p)  (make dielectric    (index (+ index-min (* 0.5 (- index-max index-min)			   (+ 1 (cos (* 2 pi (vector3-x p)))))))))(set! geometry-lattice (make lattice (size 1 no-size no-size))) ; 1d cell; We'll just make it the default material, so that it goes everywhere.(set! default-material (make material-function (material-func eps-func)))(set! k-points (interpolate 9 (list (vector3 0 0 0) (vector3 0.5 0 0))))(set-param! resolution 32)(set-param! num-bands 8); the TM and TE bands are degenerate, so we only need TM:(run-tm)