Help me fix my code for calculating the band gap of perfect photonic crystal

this is my code to calculate the band gap of perfect photonic crystal ,the boundary condition is period condition,but it don't work well ,there are some bugs ,the most difficult problem for me is that i can't get the correct frequency from the field evolution if you run the code you will get fequency graph,there are so many peaks that i can identify those correct frequencies , who can help me ,please .i have work on this code for weeks .i will be mad about it .

i run the program but it runs for along time and i didn't get any graphs
and i get
ans=15
ans=16
ans=15
ans=16 ..... and so on
if this is unnatural please correct such error first

there are some comments didn't clear could you please rewrite them in English
so that any one can read it to help you

i will wait your reply

why didn't you reply?
Do you finish the program i hope so.