Ambrosio, Luigi; Pallara, Diego Partial regularity of free discontinuity sets. I. (English) Zbl 0896.49023 Ann. Sc. Norm. Super. Pisa, Cl. Sci., IV. Ser. 24, No. 1, 1-38 (1997). The authors consider a class of perturbations of the functional \[ F(u,K)=\int_{\Omega\setminus K}|\nabla u|^2dx+{\mathcal H}^{n-1}(K) \] where \(\Omega\in\mathbb{R}^n\) is an open set, \(K\) is a variable closed subset of \(\Omega\), \(u\) is a smooth (\(C^1\)) function outside \(K\) and \({\mathcal H}^{n-1}\) stands for the \((n-1)\)-dimensional Hausdorff measure. This class encompasses the so-called Mumford-Shah functional \[ G(u,K)=\int_{\Omega\setminus K}[|\nabla u|^2+(u-g)^2]\;dx+{\mathcal H}^{n-1}(K), \] (with \(g\in L^\infty(\Omega)\)), which in the two dimensional case was proposed as a variational model of image segmentation. The authors prove that if \((u,K)\) is a quasi minimizing pair for the functional \(F\) and \(|\nabla u|\) belongs to the Morrey space \(L^{2,\lambda}(\Omega)\) for some \(\lambda>n-1\), then the set \(K\) is a \(C^{1,\alpha}\) hypersurface outside a relatively closed, \({\mathcal H}^{n-1}\)-negligible singular set. The problem of regularity of the “minimal” set \(K\) (of quasi-minimizers) will be treated in full generality (without assumption \(|\nabla u|\in L^{2,\lambda}(\Omega)\)) in the second part of the paper (see the review of the Part II below). Some indications on possible applications of the techniques developed in this paper to more general classes of functionals are also given. Reviewer: Z.Denkowski (Kraków) Cited in 2 ReviewsCited in 17 Documents MSC: 49Q20 Variational problems in a geometric measure-theoretic setting 49J10 Existence theories for free problems in two or more independent variables Keywords:spaces SBV of special functions of bounded variation; free discontinuity problems; variational models of image segmentation; quasi-minimizers; Mumford-Shah functional Citations:Zbl 0896.49024 × Cite Format Result Cite Review PDF Full Text: EuDML References: [1] W.K. Allard, On the first variation of a varifold, Ann. of Math. 95 (1972), 417-491. Zbl0252.49028 MR307015 · Zbl 0252.49028 · doi:10.2307/1970868 [2] L. Ambrosio, A compactness theorem for a new class of functions of bounded variation, Boll. Un. Mat. Ital.B3 (1989), 857-881. Zbl0767.49001 MR1032614 · Zbl 0767.49001 [3] L. Ambrosio, Existence theory for a new class of variational problems, Arch. Rational Mech. Anal. 111 (1990), 291-322. 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