Abstract: In this paper, we discuss the extended graphical frepresentation of the fraction of a complex variable s

Where K is confined to be real. Three figures of the above fraction can be used in feedback systems as well as to study the properties of figures for any one coefficient of a characteristic equation as a real parameter. It is easy to prove the following theorem:

have the same root locus.By this graphical theory, we find out that if the zeros and poles of a fraction are alternatively placed on the axis x, then there is no complex root locus of this fraction, therefore the state of such a system is always non-oscillatory; Using these figures of this fraction, we can discuss its stable interval systematically.

Key words: nonlinear, stochastic vibration, energy, equivalent linearization