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Polyconvex functionals and maximum principle
Mathematics in Engineering 2023, 5(4): 1-10
Published: 15 August 2023
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Let us consider continuous minimizers u : Ω ¯ R n R n of

F ( v ) = Ω [ | D v | p + | d e t D v | r ] d x ,

with p > 1 and r > 0; then it is known that every component u α of u = ( u 1 , . . . , u n ) enjoys maximum principle: the set of interior points x, for which the value u α ( x ) is greater than the supremum on the boundary, has null measure, that is, L n ( { x Ω : u α ( x ) > sup Ω u α } ) = 0. If we change the structure of the functional, it might happen that the maximum principle fails, as in the case

F ( v ) = Ω [ max { ( | D v | p 1 ) ; 0 } + | d e t D v | r ] d x ,

with p > 1 and r > 0. Indeed, for a suitable boundary value, the set of the interior points x, for which the value u α ( x ) is greater than the supremum on the boundary, has a positive measure, that is L n ( { x Ω : u α ( x ) > sup Ω u α } ) > 0. In this paper we show that the measure of the image of these bad points is zero, that is L n ( u ( { x Ω : u α ( x ) > sup Ω u α } ) ) = 0, provided p > n. This is a particular case of a more general theorem.

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