Point-gap topology and braids in photonic crystals using COMSOL with MATLAB scripting

MATLAB/ COMSOL scripts for studying point-gap topology / braiding in photonic crystals. I use COMSOL server and automate scripts using MATLAB. This repo was helpful: https://github.com/xiumingzhang/photonic-bandgap-comsol-matlab

Steps

1. Open COMSOL server from local computer
2. Run comsol_init.m script (used https://www.youtube.com/watch?v=7E7g0SHc8c8&t)
3. You can make your geometry etc. in COMSOL. Then go files 'Compact history' (otherwise code is very long!) and save as model file for MATLAB
4. Copy and paste from the matlab file what you need. You can edit things such as model.param.set('epsa', num2str(epsa)); in order to automate changing variables

Files

The script script_band_diagram_and_braid.m uses helper functions solve_band_diagram_and_braid.m, plot_band_diagram_and_braid.m, save_band_diagram_and_braid.m, helper_sweepkx_upd.m and helper_sweepky_upd.m to plot the eigenvalue braids for some loop or path in the Brillouin zone for a 2D photonic crystal model which is in the models folder. It also plots the the complex band diagram (which is the braid projection from the (Im(w), Re(w)) plane)