How to get the propagation constant(eigenvalue) ?

[Yannigi]

Hi, Doctor Lu

I cannot understand how you calculate the propagation constant in your file "ob1_wgmode.m". It seems you only use just sevaral lines of code to solve it. Could you please offer me some relevant hints on how to understand it? I even do not know where I can find related knowledge.

Best wishes and many thanks!
Yang LIU