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1
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Permutations preserving sums of rearranged real series

100%
Wituła R.
Open Mathematics
|
2013
|
tom 11
|
nr 5
956-965
EN
The aim of this paper is to discuss one of the most interesting and unsolved problems of the real series theory: rearrangements that preserve sums of series. Certain hypothesis about combinatorial description of the corresponding permutations is presented and basic algebraic properties of the family $\mathfrak{S}_0 $, introduced by it, are investigated.
2
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Four dimensional matrix characterization of double oscillation via RH-conservative and RH-multiplicative matrices

100%
Patterson R., Lemma M.
Open Mathematics
|
2008
|
tom 6
|
nr 4
581-594
EN
In 1939 Agnew presented a series of conditions that characterized the oscillation of ordinary sequences using ordinary square conservative matrices and square multiplicative matrices. The goal of this paper is to present multidimensional analogues of Agnew’s results. To accomplish this goal we begin by presenting a notion for double oscillating sequences. Using this notion along with square RH-conservative matrices and square RH-multiplicative matrices, we will present a series of characterization of this sequence space, i.e. we will present several necessary and sufficient conditions that assure us that a square RH-multiplicative(square RH-conservative) be such that $$ P - \mathop {limsup}\limits_{(m,n) \to \infty ;(\alpha ,\beta ) \to \infty } \left| {\sigma _{m,n} - \sigma _{\alpha ,\beta } } \right| \leqslant P - \mathop {limsup}\limits_{(m,n) \to \infty ;(\alpha ,\beta ) \to \infty } \left| {s_{m,n} - s_{\alpha ,\beta } } \right| $$ for each double real bounded sequences {s k;l} where $$ \sigma _{m,n} = \sum\limits_{k,l = 1,1}^{\infty ,\infty } {a_{m,n,k,l,} s_{k,l} } . $$ In addition, other implications and variations are also presented.
3
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Matrix characterization of oscillation for double sequences

100%
Patterson R., Connor J., Kline J.
Open Mathematics
|
2008
|
tom 6
|
nr 3
488-496
EN
The notion of oscillation for ordinary sequences was presented by Hurwitz in 1930. Using this notion Agnew and Hurwitz presented regular matrix characterization of the resulting sequence space. The primary goal of this article is to extend this definition to double sequences, which grants us the following definition: the double oscillation of a double sequence of real or complex number is given P-lim sup(m,n)→∞;(α,β)→∞|S m,n-S α,β|. Using this concept a matrix characterization of double oscillation sequence space is presented. Other implication and variation shall also be presented.
4
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Some new facts about group 𝒢 generated by the family of convergent permutations

100%
Wituła R., Hetmaniok E., Słota D.
Open Mathematics
|
2017
|
tom 15
|
nr 1
568-577
EN
The aim of this paper is to present some new and essential facts about group 𝒢 generated by the family of convergent permutations, i.e. the permutations on ℕ preserving the convergence of series of real terms. We prove that there exist permutations preserving the sum of series which do not belong to 𝒢. Additionally, we show that there exists a family G (possessing the cardinality equal to continuum) of groups of permutations on ℕ such that each one of these groups is different than 𝒢 and is composed only from the permutations preserving the sum of series. This result substantially strengthens some old Pleasants’ result.
5
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Lacunary equi-statistical convergence of positive linear operators

76%
Aktuğlu H., Gezer H.
Open Mathematics
|
2009
|
tom 7
|
nr 3
558-567
EN
In this paper, the concept of lacunary equi-statistical convergence is introduced and it is shown that lacunary equi-statistical convergence lies between lacunary statistical pointwise and lacunary statistical uniform convergence. Inclusion relations between equi-statistical and lacunary equi-statistical convergence are investigated and it is proved that, under some conditions, lacunary equi-statistical convergence and equi-statistical convergence are equivalent to each other. A Korovkin type approximation theorem via lacunary equi-statistical convergence is proved. Moreover it is shown that our Korovkin type approximation theorem is a non-trivial extension of some well-known Korovkin type approximation theorems. Finally the rates of lacunary equi-statistical convergence by the help of modulus of continuity of positive linear operators are studied.
6
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Multigeometric sequences and Cantorvals

76%
Bartoszewicz A., Filipczak M., Szymonik E.
Open Mathematics
|
2014
|
tom 12
|
nr 7
1000-1007
EN
For a sequence x ∈ l 1\c 00, one can consider the achievement set E(x) of all subsums of series Σn=1∞ x(n). It is known that E(x) has one of the following structures: a finite union of closed intervals, a set homeomorphic to the Cantor set, a set homeomorphic to the set T of subsums of Σn=1∞ x(n) where c(2n − 1) = 3/4n and c(2n) = 2/4n (Cantorval). Based on ideas of Jones and Velleman [Jones R., Achievement sets of sequences, Amer. Math. Monthly, 2011, 118(6), 508–521] and Guthrie and Nymann [Guthrie J.A., Nymann J.E., The topological structure of the set of subsums of an infinite series, Colloq. Math., 1988, 55(2), 323–327] we describe families of sequences which contain, according to our knowledge, all known examples of x with E(x) being Cantorvals.
7
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On sequences not enjoying Schur’s property

76%
Jiménez-Rodríguez P.
Open Mathematics
|
2017
|
tom 15
|
nr 1
233-237
EN
Here we proved the existence of a closed vector space of sequences - any nonzero element of which does not comply with Schur’s property, that is, it is weakly convergent but not norm convergent. This allows us to find similar algebraic structures in some subsets of functions.
8
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Extended Real-Valued Double Sequence and Its Convergence

76%
Endou N.
Formalized Mathematics
|
2015
|
tom 23
|
nr 3
253-277
EN
In this article we introduce the convergence of extended realvalued double sequences [16], [17]. It is similar to our previous articles [15], [10]. In addition, we also prove Fatou’s lemma and the monotone convergence theorem for double sequences.
9
Content available remote

Tauberian theorems for statistically (C,1,1) summable double sequences of fuzzy numbers

64%
Önder Z., Çanak İ., Totur Ü.
Open Mathematics
|
2017
|
tom 15
|
nr 1
EN
In this paper, we prove that a bounded double sequence of fuzzy numbers which is statistically convergent is also statistically (C, 1, 1) summable to the same number. We construct an example that the converse of this statement is not true in general. We obtain that the statistically (C, 1, 1) summable double sequence of fuzzy numbers is convergent and statistically convergent to the same number under the slowly oscillating and statistically slowly oscillating conditions in certain senses, respectively.
10
Content available remote

An accurate approximation of zeta-generalized-Euler-constant functions

52%
Lampret V.
Open Mathematics
|
2010
|
tom 8
|
nr 3
488-499
EN
Zeta-generalized-Euler-constant functions, $$ \gamma \left( s \right): = \sum\limits_{k = 1}^\infty {\left( {\frac{1} {{k^s }} - \int_k^{k + 1} {\frac{{dx}} {{x^s }}} } \right)} $$ and $$ \tilde \gamma \left( s \right): = \sum\limits_{k = 1}^\infty {\left( { - 1} \right)^{k + 1} \left( {\frac{1} {{k^s }} - \int_k^{k + 1} {\frac{{dx}} {{x^s }}} } \right)} $$ defined on the closed interval [0, ∞), where γ(1) is the Euler-Mascheroni constant and $$ \tilde \gamma $$(1) = ln $$ \frac{4} {\pi } $$, are studied and estimated with high accuracy.
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