We consider finite element approximations to the optimal constant for the Hardy inequality with exponent p=2p=2 in bounded domains of dimension n=1n=1 or n≥3n\geq 3. For finite element spaces of piecewise linear and continuous functions on a mesh of size hh, we prove that the approximate Hardy constant converges to the optimal Hardy constant at a rate proportional to 1/∣log⁡h∣21/|\log h|^2. This result holds in dimension n=1n=1, in any dimension n≥3n\geq 3 if the domain is the unit ball and the finite element discretization exploits the rotational symmetry of the problem, and in dimension n=3n=3 for general finite element discretizations of the unit ball. In the first two cases, our estimates show excellent quantitative agreement with values of the discrete Hardy constant obtained computationally.

Contact details are reproduced from the original publication and may be historical.

Francesco Della Pietra

Dip. di Matematica e Applicazioni "R. Caccioppoli", Università degli Studi di Napoli "Federico II",
Napoli, Italy

f.dellapietra@unina.it

Giovanni Fantuzzi

Dept. of Mathematics, Friedrich-Alexander-Universität, Erlangen-Nürnberg, Germany

giovanni.fantuzzi@fau.de

Liviu I. Ignat

(1) Institute of Mathematics "Simion Stoilow", Romanian Academy, Bucharest, Romania
(2) Research Institute of the University of Bucharest ICUB, Bucharest, Romania

liviu.ignat@gmail.com

Alba Lia Masiello

Dip. di Matematica e Applicazioni "R. Caccioppoli", Università degli Studi di Napoli "Federico II",
Napoli, Italy

albalia.masiello@unina.it

Gloria Paoli

Dip. di Matematica e Applicazioni "R. Caccioppoli", Università degli Studi di Napoli "Federico II",
Napoli, Italy

gloria.paoli@unina.it

Enrique Zuazua

(1) Dept. of Mathematics, Friedrich-Alexander-Universität, Erlangen-Nürnberg, Germany
(2) Chair of Computational Mathematics, Fundación Deusto, Bilbao, Spain
(3) Departamento de Matemáticas, Universidad Autónoma de Madrid, Madrid, Spain

enrique.zuazua@fau.de
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F. Della Pietra, G. Fantuzzi, L. I. Ignat, A. L. Masiello, G. Paoli, E. Zuazua. “Finite Element Approximation of the Hardy Constant.” Journal of Convex Analysis 31 (2024), No. 2, 497–523. https://doi.org/10.68381/jca31027