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The original blue-and-pink-haired researcher and her star cat observe forward and backward trajectories as a terminal perturbation decays toward the initial horizon.
Pyuyi Chufeng Huang, Zikang Song

Horizon-Uniform Sensitivity and Decay of Terminal Reward Perturbations in Discrete-Time Pontryagin Systems

We study local stationary solutions of finite-horizon discrete-time Pontryagin systems near a steady extremal. Under regular stationarity, hyperbolicity of the reduced state-costate map, and scaled transversality of the endpoint conditions, the linearized boundary-value problem has a horizon-uniform Green estimate. A weighted-norm contraction argument gives existence, uniqueness, uniform Lipschitz estimates, and pointwise quadratic remainders. For graph boundary conditions, terminal reward perturbations have exponentially small effects on the initial control and the stationary objective gradient; the linear-quadratic case yields exponential convergence of Riccati matrices and initial feedback gains.

Optimal controlPontryagin systemsSensitivity analysisExponential dichotomiesDynamic programmingSymplectic methods
The original blue-and-pink-haired researcher and her star cat examine a cyclic ribbon complex, synchronized glowing cuts, and its two branched factors.
Pyuyi Chufeng Huang

Cycle-Decorated Ribbon Complexes: Cut Coproducts and Alternating-Fence Positivity

We define a two-variable specialization of the ribbon basis of noncommutative symmetric functions from cycle enumerators of an ordinary permutation and a rooted permutation, with reflection length recorded by the second variable. Its factorial multiple is realized as the shifted bigraded Euler characteristic of an equivariant ordered-set-partition complex. Total decorations determine simultaneous factorization cuts and classical ribbon-complex fibers, yielding explicit nonnegative ribbon expansions. A compatible cut coproduct is constructed, and the alternating-fence specialization is shown to have nonnegative coefficients together with controlled homological support and explicit defect-zero formulas.

Noncommutative symmetric functionsRibbon Schur functionsEquivariant homologyCut coproductsAlternating fencesOrder polynomials
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