Bilinear local controllability to the trajectories of the Fokker-Planck equation with a localized control

TL;DR

This paper establishes local controllability of the Fokker-Planck equation with localized control, introduces a new Carleman inequality, and discusses conditions for control reduction, advancing control theory for stochastic PDEs.

Contribution

It introduces a novel algebraic solvability approach on the adjoint problem and a new Carleman inequality for the Fokker-Planck equation with space-time varying coefficients.

Findings

Proves local controllability to regular trajectories.

Develops a new Carleman inequality for heat equations with localized gradient terms.

Identifies conditions where control reduction is not possible.

Abstract

This work is devoted to the control of the Fokker-Planck equation, posed on a smooth bounded domain of R^d, with a localized drift force. We prove that this equation is locally controllable to regular nonzero trajectories. Moreover, under some conditions, we explain how to reduce the number of controls around the reference control. The results are obtained thanks to a standard linearization method and the fictitious control method. The main novelties are twofold. First, the algebraic solvability is performed and used directly on the adjoint problem. We then prove a new Carleman inequality for the heat equation with a space-time varying first-order term: the right-hand side is the gradient of the solution localized on an open subset. We finally give an example of regular trajectory around which the Fokker-Planck equation is not controllable with a reduced number of controls, to highlight that our conditions are relevant.