Thank you Philip, I appreciate your hints.
My data is a computer generated data which is the reflection spectrum of a broadband light from a two layer
system. From the spectrum, I want to reconstruct the object refractive indices and thicknesses.
Would you please expalin more about your comment:"You have a couple of terms which are difference scaled (b[1 - b[2) etc. It is the difference that will (most likely) be critical to the solution. Why not reframe the model equation in terms of those deltas (perhaps even pre-scale them!)."
Also I don't understand your comment "You do have to pre-define k:=k to avoid it trying to compute a vastly large symbolic solution". I checked my program and it always consider "k" as what I defiend.
the term (zr-zs[0) has been set to zero for simplification.
Finally, would you please let me know how to obtain the beating frequency?
Thank you very much in advance