Center Conditions And Bifurcation Of Limit Cycles For A Class Of Quasi-Fourth Systems

This thesis is devoted to the problems of integral conditions, center-focus deter-mination and bifurcation of limit cycles at the origin and the infinity of a class of quasi fourth system. It is composed of three chapters.In chapter 1, it is introduced and summarized about the historical background and the present progress of problems about center-focus determination and bifurcation of limit cycles of planar polynomial differential system. At the same time, the main work of this paper is concluded is introduced.In chapter 2,it is introduced some preliminary knowledgeIn chapter 3, using an indirect method to study center conditions and bifurcation of limit cycle for a class of quasi fourth system, We obtain 4 limit cycles. It is the first time that 4 limit cycles can bifurcated from the infinity for a class of quasi fourth system.