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Changyu Zhou

Publications and source records attributed to Changyu Zhou.

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Kovalevskaya exponents of the Riccati hierarchy

We carry out a Kovalevskaya analysis of the Riccati hierarchy. We determine all indicial loci and Kovalevskaya exponents and identify a rigid recursive structure governing how free parameters enter Laurent solutions. We further identify a nontrivial quasi--homogeneous vector field commuting with the hierarchy and use it to obtain an explicit parametrization of all solutions in terms of a single polynomial. Notably, in the two-dimensional case, the same general solution is recovered by the blow-up resolution. Within this parametrization, collisions of poles correspond to degeneration limits of the principal Laurent family, through which lower indicial loci appear. Finally, negative Kovalevskaya exponents are interpreted analytically through annular Laurent expansions, which describe how different collections of poles dominate in different complex regions.

math.CA

Quasi-Homogeneous Integrable Systems: Free Parameters, Kovalevskaya Exponents, and the Painlev\'e Property

This paper investigates quasi-homogeneous integrable systems by analyzing their Laurent series solutions near movable singularities, motivated by patterns observed in Kovalevskaya exponents of four-dimensional Painlev\'e-type equations. We introduce a parameter space encoding the free coefficients in these expansions and study its deformation under a commuting quasi-homogeneous vector field. Within this framework, we derive lower indicial loci from the principal one and establish an arithmetic resonance condition on Kovalevskaya exponents that governs the emergence of fractional powers and the breakdown of the Painlev\'e property. Moreover, we construct a Frobenius manifold structure on the parameter space via the initial value map, which becomes conformal when all weights coincide. In the Hamiltonian context, we demonstrate that the induced flow on the parameter space preserves a symplectic form and yields a natural pairing of Kovalevskaya exponents. These findings unify analytic and geometric aspects of quasi-homogeneous integrable systems and offer new insights into their deformation theory and singularity structures. Our results provide a comprehensive framework applicable to the classification and analysis of Painlev\'e-type equations and related integrable models.

nlin.SI