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Mittag–Leffler Stability and Decay-Rate Enhancement for a Nabla Discrete Fractional-Order Glucose–Insulin Regulatory System with a Nonsingular Mittag–Leffler Kernel

  • Grienggrai Rajchakit

Received: 22 Jul 2026 | Revised: 02 Sep 2026 | Accepted: 10 Sep 2026 | Published: 18 Sep 2026

Abstract

We study a reduced-order, discrete-time glucose–insulin regulatory model with an intended nonsingular Mittag-Leffler memory kernel. The aim is an interpretable control-theoretic benchmark, not a patient-specific artificial-pancreas model. For the bidirectionally coupled error system, optimisation of a scalar quadratic Young-inequality estimate gives \(\lambda^* = \tfrac{1}{2}\big[(a+c) - \sqrt{(a-c)^2 + \beta^2}\big]\), where \(\beta = bL_\phi + eL_\psi\); this algebraic quantity is positive exactly when \(\beta < 2\sqrt{ac}\). At \(a = 0.6\), \(c = 0.4\), and \(\beta = 0.5\), it increases the fixed-parameter value from \(0.150\) to \(0.231\). Replacing c by \(c + k_1\) with \(k_1 = 0.6\) gives \(0.480\). Strict gain monotonicity holds for \(\beta > 0\), while the formal \(\beta = 0\) extension is nondecreasing and saturates at a. Interpretation of these values as Mittag-Leffler decay certificates remains conditional on the operator definition and comparison lemmas flagged in this proof. The delayed estimate supplies a delay-independent algebraic condition, not a delay-uniform decay rate. The disturbance estimate, if its comparison properties hold, supplies an asymptotic residual radius. An explicit lagged predictor is reproducible and admits an endpoint refinement check, but this check does not establish consistency with the stated operator. In addition, the coupled code omits the equilibrium shifts of the raw model. These operator and model-alignment issues are retained as explicit editorial queries requiring resolution before publication. No clinical performance or safety claim is made.

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Rajchakit, G. Mittag–Leffler Stability and Decay-Rate Enhancement for a Nabla Discrete Fractional-Order Glucose–Insulin Regulatory System with a Nonsingular Mittag–Leffler Kernel. Applied Nonlinear Dynamics and Vibrations 2026, 1 (1), 5.
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