Hi Werner,
I did try to substitute for a variable X and search coefficients but MathCAD doesn't replace it. So, I think it is unable to recognise e^i*theta as a function, no idea. (my knowledg about MathCAD is minimal).
About the a0vector, etc... what do you mean with transposing the argument vector? The purpose of a0vector, a1vectore, b0vector etc... is that these are unknown coefficients to be determined in a next step by solving the system against some other function. Don't exactly know what you mean with this.