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On the L 1-relaxed area of graphs of BV piecewise constant maps taking three values

  • Riccardo Scala EMAIL logo and Giuseppe Scianna
Published/Copyright: October 2, 2024

Abstract

Given a bounded open connected set Ω 2 with Lipschitz boundary, we consider the class of piecewise constant maps u taking three fixed values α , β , γ 2 , vertices of an equilateral triangle; for any u in this class, using a weak notion of Jacobian determinant valid for BV functions, we give a precise description of Det ( u ) and show that the relaxed graph area of u is bounded from above by a quantity related to the flat norm of Det ( u ) . The provided upper bound allows to show the validity of a De Giorgi conjecture regarding the relaxed area functional when one restricts to this class of piecewise constant functions.


Dedicated to Giovanni Bellettini for his 60th birthday



Communicated by Irene Fonseca


Funding statement: Riccardo Scala is member of the Gruppo Nazionale per l’Analisi Matematica, la Probabilitàa e le loro Applicazioni (GNAMPA) of the Istituto Nazionale di Alta Matematica (INdAM), and joins the project CUP-E53C22001930001. We also acknowledge the partial financial support of the F-CUR (project number 2262 – 2022 – SR – CONRICMIURPC – FCUR2022-002) of the University of Siena, and the financial support of PRIN 2022PJ9EFL “Geometric Measure Theory: Structure of Singular Measures, Regularity Theory and Applications in the Calculus of Variations”. The latter has been funded by the European Union under NextGenerationEU (funding organization: Italian Miur, Missione 4, Componente 2 – CUP:E53D23005860006).

A Appendix

We collect here two useful observations. The first one consists in the following lemma, whose content can be found in [19] (see also references therein):

Lemma A.1.

Let U R 2 be a relatively compact set. Then for a.e. δ > 0 the δ-neighborhood U δ of U has Lipschitz boundary.

As a second remark, we see that we can equivalently relax the area functional using W loc 1 , functions instead of C 1 maps:

Lemma A.2.

Let Ω R 2 be a Lipschitz domain and u L 1 ( Ω ; R 2 ) . Then

(A.1) 𝒜 ¯ ( u , Ω ) = inf { lim inf k + 𝔸 ( v k , Ω ) : v k W loc 1 , ( Ω ; 2 ) , v k u in  L 1 ( Ω ; 2 ) } .

This follows from the fact that for v W loc 1 , ( Ω ; 2 ) it holds 𝒜 ¯ ( v , Ω ) = 𝔸 ( v , Ω ) (see [1]), which trivially implies the inequality in the formula above. The opposite inequality is obtained by simply observing that

C 1 ( Ω ; 2 ) W loc 1 , ( Ω ; 2 ) .

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Received: 2023-10-08
Accepted: 2024-06-09
Published Online: 2024-10-02
Published in Print: 2025-04-01

© 2024 Walter de Gruyter GmbH, Berlin/Boston

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