  A short introduction of a relation between a Green's function and a quantum
wave impedance function as well as its application to a determination of
eigenenergies and eigenfunctions of a quatum-mechanical system is provided.
Three different approaches, namely a classical approach based on a direct
solving of a Shr\"{o}dinger equation, a transfer matrix method and a quantum
wave impedance technique, for a calculation of eigenenergies and eigenfunctions
of a quantum mechanical nonsymmetric single well system are considered. A
comparision of these approaches gives the possibility to clarify advantages and
drawbacks of each method which is useful especially for teaching and learning
purposes.
