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Merlin Schmitz

Publications and source records attributed to Merlin Schmitz.

4 recordsLinked to original sources
arXiv2026

A class of port-Hamiltonian systems with general time delays

We define a class of infinite dimensional linear port-Hamiltonian delay systems, give a characterization for such systems, and provide an easily verifiable sufficient condition to belong to this class, thereby extending the study by Breiten, Hinsen and Unger in [IEEE Trans. Autom. Control vol. 69, no. 12 (2024), pp. 8924-8930, doi: 10.1109/TAC.2024.3464332]. The results rely on the operator semigroup theoretic treatment of linear delay PDEs.

math.FA↗
arXiv2025

Dissipativity-based time domain decomposition for optimal control of hyperbolic PDEs

We propose a time domain decomposition approach to optimal control of partial differential equations (PDEs) based on semigroup theoretic methods. We formulate the optimality system consisting of two coupled forward-backward PDEs, the state and adjoint equation, as a sum of dissipative operators, which enables a Peaceman-Rachford-type fixed-point iteration. The iteration steps may be understood and implemented as solutions of many decoupled, and therefore highly parallelizable, time-distributed optimal control problems. We prove the convergence of the state, the control, and the corresponding adjoint state in function space. Due to the general framework of $C_0$-(semi)groups, the results are particularly well applicable, e.g., to hyperbolic equations, such as beam or wave equations. We illustrate the convergence and efficiency of the proposed method by means of two numerical examples subject to a 2D wave equation and a 3D heat equation.

math.OC↗
arXiv2022

On exponential splitting methods for semilinear abstract Cauchy problems

Due to the seminal works of Hochbruck and Ostermann exponential splittings are well established numerical methods utilizing operator semigroup theory for the treatment of semilinear evolution equations whose principal linear part involves a sectorial operator with angle greater than ${\pi}/2$ (meaning essentially the holomorphy of the underlying semigroup). The present paper contributes to this subject by relaxing on the sectoriality condition, but in turn requiring that the semigroup operators act consistently on an interpolation couple (or on a scale of Banach spaces). Our conditions (on the semigroup and on the semilinearity) are inspired by the approach of T. Kato to the local solvability of the Navier-Stokes equation, where the $L^p-L^r$ smoothing of the Stokes semigroup was fundamental. The present abstract operator theoretic result is applicable for this latter problem (as was already the result of Ostermann and Hochbruck), or more generally in the setting of holomorphic semigroups, but also allows the consideration of examples, such as non-analytic Ornstein-Uhlenbeck semigroups or the Navier-Stokes flow around rotating bodies.

math.FA↗