Browsing Artículos de revista DEIM - EIMS Aldizkari artikuluak by Author "Ansorena, José L."
Now showing items 1-20 of 27
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Addendum to "uniqueness of unconditional basis of infinite direct sums of quasi-Banach spaces"
Albiac Alesanco, Fernando José
; Ansorena, José L. (Springer, 2022)
Artículo / Artikulua 
After [Uniqueness of unconditional basis of infinite direct sums of quasi-Banach spaces, Positivity 26 (2022), Paper no. 35] was published, we realized that Theorem 4.2 therein, when combined with work of Casazza and Kalton ... -
Asymptotic greediness of the Haar system in the spaces Lp[0 , 1] , 1< p< ∞
Albiac Alesanco, Fernando José ; Ansorena, José L.; Berná, Pablo M. (Springer, 2019)
Artículo / Artikulua
Our aim in this paper is to attain a sharp asymptotic estimate for the greedy constant Cg[H(p), Lp] of the (normalized) Haar system H(p) in Lp[0 , 1] for 1 < p < ∞. We will show that the super-democracy constant of H(p) ... -
Bidemocratic bases and their connections with other greedy-type bases
Albiac Alesanco, Fernando José ; Ansorena, José L.; Berasategui, Miguel; Berná, Pablo M.; Lassalle, Silvia (Springer, 2023)
Artículo / Artikulua
In nonlinear greedy approximation theory, bidemocratic bases have traditionally played the role of dualizing democratic, greedy, quasi-greedy, or almost greedy bases. In this article we shift the viewpoint and study them ... -
Building highly conditional almost greedy and quasi-greedy bases in Banach spaces
Albiac Alesanco, Fernando José ; Ansorena, José L.; Dilworth, S. J.; Kutzarova, Denka (Elsevier, 2019)
Artículo / Artikulua
It is known that for a conditional quasi-greedy basis B in a Banach space X, the associated sequence (k(m)[B](m=1)(infinity) of its conditionality constants verifies the estimate k(m)[B] = O(log m) and that if the reverse ... -
Conditional quasi-greedy bases in non-superreflexive Banach spaces
Albiac Alesanco, Fernando José ; Ansorena, José L.; Wojtaszczyk, Przemyslaw (Springer, 2019)
Artículo / Artikulua
For a conditional quasi-greedy basis B in a Banach space, the associated conditionality constants km[B] verify the estimate km[B]=O(logm). Answering a question raised by Temlyakov, Yang, and Ye, several authors have studied ... -
Democracy of quasi-greedy bases in p-Banach spaces with applications to the efficiency of the thresholding greedy algorithm in the hardy spaces Hp(Dd)
Albiac Alesanco, Fernando José ; Ansorena, José L.; Bello, Glenier (Cambridge University Press, 2023)
Artículo / Artikulua
We use new methods, specific for non-locally convex quasi-Banach spaces, to investigate when the quasi-greedy bases of a -Banach space for 0 < p < p are democratic. The novel techniques we obtain permit to show in particular ... -
Elton's near unconditionality of bases as a threshold-free form of greediness
Albiac Alesanco, Fernando José ; Ansorena, José L.; Berasategui, Miguel (Elsevier, 2023)
Artículo / Artikulua
Elton's near unconditionality and quasi-greediness for largest coefficients are two properties of bases that made their appearance in functional analysis from very different areas of research. One of our aims in this note ... -
Embeddability of ℓp and bases in Lipschitz free p-spaces for 0 < p ≤ 1
Albiac Alesanco, Fernando José ; Ansorena, José L.; Cúth, Marek; Doucha, Michal (Elsevier, 2020)
Artículo / Artikulua
Our goal in this paper is to continue the study initiated by the authors in of the geometry of the Lipschitz free p-spaces over quasimetric spaces for 0 < p ≤ 1, denoted Fp(M). Here we develop new techniques to show that, ... -
Existence of almost greedy bases in mixed-norm sequence and matrix spaces, including besov spaces
Albiac Alesanco, Fernando José ; Ansorena, José L.; Bello, Glenier; Wojtaszczyk, Przemyslaw (Springer, 2023)
Artículo / Artikulua
We prove that the sequence spaces lp ⊕ lq and the spaces of infinite matrices lp(lq ), lq l(p) and ( ∞ n=1 n lp)lq , which are isomorphic to certain Besov spaces, have an almost greedy basis whenever 0 < p < 1 < q < ∞. ... -
Greedy approximation for biorthogonal systems in quasi-Banach spaces
Albiac Alesanco, Fernando José ; Ansorena, José L.; Berná, Pablo M.; Wojtaszczyk, Przemyslaw (Instytut Matematyczny, 2021)
Artículo / Artikulua
The general problem addressed in this work is the development of a systematic study of the thresholding greedy algorithm for general biorthogonal systems in quasi-Banach spaces from a functional-analytic point of view. If ... -
Lipschitz algebras and Lipschitz-Free spaces over unbounded metric spaces
Albiac Alesanco, Fernando José ; Ansorena, José L.; Cúth, Marek; Doucha, Michal (Oxford University Press, 2021)
Artículo / Artikulua
We investigate a way to turn an arbitrary (usually, unbounded) metric space M into a bounded metric space B in such a way that the corresponding Lipschitz-free spaces F(M) and F(B) are isomorphic. The construction we provide ... -
Lipschitz free p-spaces for 0 < p < 1
Albiac Alesanco, Fernando José ; Ansorena, José L.; Cúth, Marek; Doucha, Michal (SpringerHebrew University Magnes Press, 2020)
Artículo / Artikulua
This paper initiates the study of the structure of a new class of p-Banach spaces, 0 <p < 1, namely the Lipschitz free p-spaces (alternatively called Arens—Eells p-spaces) Fp(M) over p-metric spaces. We systematically ... -
Lipschitz free spaces isomorphic to their infinite sums and geometric applications
Albiac Alesanco, Fernando José ; Ansorena, José L.; Cúth, Marek; Doucha, Michal (American Mathematical Society, 2021)
Artículo / Artikulua
We find general conditions under which Lipschitz-free spaces over metric spaces are isomorphic to their infinite direct _1-sum and exhibit several applications. As examples of such applications we have that Lipschitz-free ... -
New parameters and Lebesgue-type estimates in greedy approximation
Albiac Alesanco, Fernando José ; Ansorena, José L.; Berná, Pablo M. (Cambridge University Press, 2022)
Artículo / Artikulua
The purpose of this paper is to quantify the size of the Lebesgue constants (𝑳𝑚)∞ 𝑚=1 associated with the thresholding greedy algorithm in terms of a new generation of parameters that modulate accurately some features ... -
Non-superreflexivity of Garling sequence spaces and applications to the existence of special types of conditional bases
Albiac Alesanco, Fernando José ; Ansorena, José L.; Dilworth, S. J.; Kutzarova, Denka (Instytut Matematyczny, 2020)
Artículo / Artikulua
We settle in the negative the problem of the superreflexivity of Garling sequence spaces by showing that they contain a complemented subspace isomorphic to a non-superreflexive mixed-norm sequence space. As a by-product, ... -
On a 'philosophical' question about Banach envelopes
Albiac Alesanco, Fernando José ; Ansorena, José L.; Wojtaszczyk, Przemyslaw (Springer, 2021)
Artículo / Artikulua
We show how to construct non-locally convex quasi-Banach spaces X whose dual separates the points of a dense subspace of X but does not separate the points of X. Our examples connect with a question raised by Pietsch (Rev ... -
On certain subspaces of p for 0 < p ≤ 1 and their applications to conditional quasi-greedy bases in p-Banach spaces
Albiac Alesanco, Fernando José ; Ansorena, José L.; Wojtaszczyk, Przemyslaw (Springer, 2021)
Artículo / Artikulua
We construct for each 0<p≤1 an infinite collection of subspaces of ℓp that extend the example of Lindenstrauss (Bull. Acad. Polon. Sci. Sér. Sci. Math. Astronom. Phys. 12, 539–542, 1964) of a subspace of ℓ1 with no ... -
On the permutative equivalence of squares of unconditional bases
Albiac Alesanco, Fernando José ; Ansorena, José L. (Elsevier, 2022)
Artículo / Artikulua
We prove that if the squares of two unconditional bases are equivalent up to a permutation, then the bases themselves are permutatively equivalent. This settles a twenty-five year-old question raised by Casazza and Kalton ... -
Projections and unconditional bases in direct sums of ℓp SPACES, 0<p≤∞
Albiac Alesanco, Fernando José ; Ansorena, José L. (Wiley, 2021)
Artículo / Artikulua
We show that every unconditional basis in a finite direct sum ⊕p∈Aℓp , with A ⊂ (0,∞], splits into unconditional bases of each summand. This settles a 40 years old question raised in 'A. Ortyński, Unconditional bases in ... -
Quasi-greedy bases in ℓp (0 < p < 1) are democratic
Albiac Alesanco, Fernando José ; Ansorena, José L.; Wojtaszczyk, Przemyslaw (Elsevier, 2020)
Artículo / Artikulua
The list of known Banach spaces whose linear geometry determines the (nonlinear) democracy functions of their quasi-greedy bases to the extent that they end up being democratic, reduces to c0, ℓ2, and all separable L1-spaces. ...
