treated in more detail. They are just specimen of larger classes of
schemes. Es- sentially, we have to distinguish between semi-analytical
methods, discretiza- tion methods, and lumped circuit models. The
semi-analytical methods and the discretization methods start directly
from Maxwell's equations. Semi-analytical methods are concentrated on
the analytical level: They use a computer only to evaluate expressions
and to solve resulting linear algebraic problems. The best known
semi-analytical methods are the mode matching method, which is described
in subsection 2. 1, the method of integral equations, and the method of
moments. In the method of integral equations, the given boundary value
problem is transformed into an integral equation with the aid of a
suitable Greens' function. In the method of moments, which includes the
mode matching method as a special case, the solution function is
represented by a linear combination of appropriately weighted basis
func- tions. The treatment of complex geometrical structures is very
difficult for these methods or only possible after geometric
simplifications: In the method of integral equations, the Greens
function has to satisfy the boundary condi- tions. In the mode matching
method, it must be possible to decompose the domain into subdomains in
which the problem can be solved analytically, thus allowing to find the
basis functions. Nevertheless, there are some ap- plications for which
the semi-analytic methods are the best suited solution methods. For
example, an application from accelerator physics used the mode matching
technique (see subsection 5. 4).