Classification of the centers and isochronicity for a class of quartic polynomial differential systems

In this paper, the conditions of center and isochronous center at the origin for a class of planar quartic differential systems are studied. At first, a constructive theorem of singular point quantities is presented, which plays an important role in simplifying periodic constants. The sufficient and necessary conditions for the origin of the systems being a center are obtained. Then a complete classification of the sufficient and necessary conditions are given for the origin of the systems being an isochronous center.