Unfoldings and Bifurcations of Polynomial Differential Systems

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We investigate the versal unfolding and bifurcations of planar polynomial differential systems having some topological structure. Specially, we classify the systems of high degree which have centers or degenerate equilibria. Then we study the degeneracy of the system and prove the existence of versal unfoldings. All possible bifurcations of unfolding systems will be discussed and topological phase portraits of the systems are presented. Finally, we give a rigourous mathematical explanation for our results in some bio-mathematical models.