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Examples of functions -extendable for each finite, but not -extendable

Wiesław Pawłucki (1998)

Banach Center Publications

In Example 1, we describe a subset X of the plane and a function on X which has a k -extension to the whole 2 for each finite, but has no -extension to 2 . In Example 2, we construct a similar example of a subanalytic subset of 5 ; much more sophisticated than the first one. The dimensions given here are smallest possible.

Explicit Construction of Piecewise Affine Mappings with Constraints

Waldemar Pompe (2010)

Bulletin of the Polish Academy of Sciences. Mathematics

We construct explicitly piecewise affine mappings u:ℝ ⁿ → ℝ ⁿ with affine boundary data satisfying the constraint div u = 0. As an application of the construction we give short and direct proofs of the main approximation lemmas with constraints in convex integration theory. Our approach provides direct proofs avoiding approximation by smooth mappings and works in all dimensions n ≥ 2. After a slight modification of our construction, the constraint div u = 0 can be turned into det Du = 1, giving...

Extending n times differentiable functions of several variables

Hajrudin Fejzić, Dan Rinne, Clifford E. Weil (1999)

Czechoslovak Mathematical Journal

It is shown that n times Peano differentiable functions defined on a closed subset of m and satisfying a certain condition on that set can be extended to n times Peano differentiable functions defined on m if and only if the n th order Peano derivatives are Baire class one functions.

Extending o-minimal Fréchet derivatives

Andreas Fischer (2007)

Annales Polonici Mathematici

We investigate several extension properties of Fréchet differentiable functions defined on closed sets for o-minimal expansions of real closed fields.

Extension of Lipschitz functions defined on metric subspaces of homogeneous type.

Alexander Brudnyi, Yuri Brudnyi (2006)

Revista Matemática Complutense

If a metric subspace Mº of an arbitrary metric space M carries a doubling measure μ, then there is a simultaneous linear extension of all Lipschitz functions on Mº ranged in a Banach space to those on M. Moreover, the norm of this linear operator is controlled by logarithm of the doubling constant of μ.

Extension of the Two-Variable Pierce-Birkhoff conjecture to generalized polynomials

Charles N. Delzell (2010)

Annales de la faculté des sciences de Toulouse Mathématiques

Let h : n be a continuous, piecewise-polynomial function. The Pierce-Birkhoff conjecture (1956) is that any such h is representable in the form sup i inf j f i j , for some finite collection of polynomials f i j [ x 1 , ... , x n ] . (A simple example is h ( x 1 ) = | x 1 | = sup { x 1 , - x 1 } .) In 1984, L. Mahé and, independently, G. Efroymson, proved this for n 2 ; it remains open for n 3 . In this paper we prove an analogous result for “generalized polynomials” (also known as signomials), i.e., where the exponents are allowed to be arbitrary real numbers, and not just natural numbers;...

Extension to copulas and quasi-copulas as special 1 -Lipschitz aggregation operators

Erich Peter Klement, Anna Kolesárová (2005)

Kybernetika

Smallest and greatest 1 -Lipschitz aggregation operators with given diagonal section, opposite diagonal section, and with graphs passing through a single point of the unit cube, respectively, are determined. These results are used to find smallest and greatest copulas and quasi-copulas with these properties (provided they exist).

Extensions of the representation theorems of Riesz and Fréchet

João C. Prandini (1993)

Mathematica Bohemica

We present two types of representation theorems: one for linear continuous operators on space of Banach valued regulated functions of several real variables and the other for bilinear continuous operators on cartesian products of spaces of regulated functions of a real variable taking values on Banach spaces. We use generalizations of the notions of functions of bounded variation in the sense of Vitali and Fréchet and the Riemann-Stieltjes-Dushnik or interior integral. A few applications using geometry...

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