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Wyświetlanie 1-15 z 604
Tytuł:
Equivalent definitions for the measurability of a multivariate function and Filippovs lemma
Autorzy:
Idzik, Adam
Powiązania:
https://bibliotekanauki.pl/articles/748427.pdf
Data publikacji:
1979
Wydawca:
Polskie Towarzystwo Matematyczne
Tematy:
Measurable and nonmeasurable functions, sequences of measurable functions, modes of convergence
Opis:
W wielu pracach, w których pojawia się pojęcie mierzalności funkcji wielowartościowej, autorzy zazwyczaj formułują jedną definicję mierzalności i nie podkreślają związków z innymi definicjami, chociaż istnieje ich wiele. Zakładając, że przestrzeń, w której leżą wartości funkcji wielowartościowej, przyjmującej tylko zbiory domknięte, jest metryczna i zwarta, udowodnimy, że wszystkie bardziej znane definicje mierzaluości funkcji wielowartościowej są równoważne.
From the text: "In the many papers in which the concept of measurability of a multivariate function arises, the authors usually formulate one definition of measurability and ignore its connections with other definitions. Assuming that the space, in which the values of the multivariate function lie, which admits only a closed set, is metric and compact we prove that all well-known definitions of measurability of multivariate functions are equivalent. "A. F. Filippov's lemma was first formulated in 1959 [Vestnik Moskov. Univ. Ser. Mat. Meh. Astr. Fiz. Him. 1959, no. 2, 25–32; MR0122650] and was later generalized by many others, in particular by W. Furakawa [Ann. Math. Statist. 43 (1972), 1612–1622; MR0371418], C. J. Himmelberg [Fund. Math. 87 (1975), 53–72; MR0367142] and C. Olech [Bull. Acad. Polon Sci. Sér. Sci. Math. Astronom. Phys. 13 (1965), 317–321; MR0199338]. Using various definitions of measurability of a multivariate function (whose equivalence we prove beforehand) we introduce two theorems on the existence of a measurable implicit function. These theorems generalize Furakawa's theorem [op. cit.] which is a reformulation of Olech's theorem [op. cit.] for Borel measurability.''
Źródło:
Mathematica Applicanda; 1979, 7, 14
1730-2668
2299-4009
Pojawia się w:
Mathematica Applicanda
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Effective difference schemes for the heat equation in arbitrary regions
Autorzy:
Dryja, Maksymilian
Powiązania:
https://bibliotekanauki.pl/articles/748525.pdf
Data publikacji:
1982
Wydawca:
Polskie Towarzystwo Matematyczne
Tematy:
Stability and convergence of difference methods,Error bounds
Opis:
.
In this paper the author considers the problem of the heat equation ∂u/∂t−(∂2u/∂x21+∂2u/∂x22)=f(x,t) for x∈Ω and t∈(0,T], u(x,0)=φ(x) for x∈Ω, u(x,t)=0 for x∈∂Ω and t∈[0,T]. He constructs a Crank-Nicolson and an alternating direction difference scheme on a regular mesh with steps hi (i=1,2) and τ. Linear interpolation is used for the approximation of the boundary condition. Besides stability of both schemes error estimates are derived under the condition that the derivatives ∂5u/∂t∂x4i and ∂3u/∂t3 are bounded. These estimates are: maxn∥un−yn∥A≤M(τ2+h3/2)andmaxn∥un−yn∥h≤M(τ2+h2+τh1/2+h5/2/τ). Here h=max(h1,h2), un=u(⋅,nτ), yn is the approximate value of un, ∥u∥2h=(u,u)h, (u,v)h=h1h2∑x∈Ωhu(x)v(x) (Ωh is the set of all mesh points lying in Ω), and ∥u∥2A=(u,Au)h where A is the discrete Laplace operator.
Źródło:
Mathematica Applicanda; 1982, 10, 19
1730-2668
2299-4009
Pojawia się w:
Mathematica Applicanda
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Matrices splitting the norm and their applications in the theory of stability of difference schemes
Autorzy:
Pokrzywa, Andrzej
Powiązania:
https://bibliotekanauki.pl/articles/747515.pdf
Data publikacji:
1985
Wydawca:
Polskie Towarzystwo Matematyczne
Tematy:
Matrix norms, conditioning, scaling
Norms of matrices, numerical range, applications of functional analysis to matrix theory
Stability and convergence of difference methods
Opis:
.
In a finite-dimensional real or complex linear normed space X there are characterized all the sets of operators A1,...,An which sum up to the identity operator and such that ||Aix||+...+||Anx|=||x|| for all xX. An example of application in the theory of stability of difference schemes is given.
Źródło:
Mathematica Applicanda; 1985, 13, 26
1730-2668
2299-4009
Pojawia się w:
Mathematica Applicanda
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Some problems connected with the absolute stability of explicit one-step methods
Autorzy:
Szyszkowicz, Mieczysław
Powiązania:
https://bibliotekanauki.pl/articles/748597.pdf
Data publikacji:
1985
Wydawca:
Polskie Towarzystwo Matematyczne
Tematy:
Stability and convergence of numerical methods
Opis:
.
Regions of absolute stability for several examples of Runge-Kutta methods, Bobkov methods, Richardson extrapolation of Runge-Kutta methods are investigated. For the Richardson extrapolation of Runge-Kutta methods the method with maximal order of convergence is found.
Źródło:
Mathematica Applicanda; 1985, 13, 26
1730-2668
2299-4009
Pojawia się w:
Mathematica Applicanda
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Difference method for a nonlinear parabolic equation of second order in two space variables
Autorzy:
Kawecki, Roman
Powiązania:
https://bibliotekanauki.pl/articles/747916.pdf
Data publikacji:
1990
Wydawca:
Polskie Towarzystwo Matematyczne
Tematy:
Finite difference methods
Stability and convergence of numerical methods
Opis:
.
A.C. Reynolds in his paper (1972) proposed a difference parametric method for solving the Fourier problem for a nonlinear parabolic equation of second order in one space variable. The paper presents a generalization of Reynolds’ method for the problem in two space variables with mixed derivatives. In this paper, Fourier problems for a general class of nonlinear parabolic equation, in QT = Q x [0, T], are studied. To solve this problem we construct a finite difference scheme with a real parameter. We prove that the solutions of certain associated finite difference equations are unique and converge to the solution of the initial-boundary value problem with 0(h^2) rate of convergence.
Źródło:
Mathematica Applicanda; 1990, 18, 32
1730-2668
2299-4009
Pojawia się w:
Mathematica Applicanda
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
A new convexity property that implies a fixed point property for $L_{1}$
Autorzy:
Lennard, Chris
Powiązania:
https://bibliotekanauki.pl/articles/1293465.pdf
Data publikacji:
1991
Wydawca:
Polska Akademia Nauk. Instytut Matematyczny PAN
Tematy:
uniform Kadec-Klee property
convergence in measure compact sets
convex sets
normal structure
Lebesgue function spaces
fixed point
nonexpansive mapping
Chebyshev centre
Opis:
In this paper we prove a new convexity property for L₁ that resembles uniform convexity. We then develop a general theory that leads from the convexity property through normal structure to a fixed point property, via a theorem of Kirk. Applying this theory to L₁, we get the following type of normal structure: any convex subset of L₁ of positive diameter that is compact for the topology of convergence locally in measure, must have a radius that is smaller than its diameter. Indeed, a stronger result holds. The Chebyshev centre of any norm bounded, convergence locally in measure compact subset of L₁ must be norm compact. Immediately from normal structure, we get a new proof of a fixed point theorem for L₁ due to Lami Dozo and Turpin.
Źródło:
Studia Mathematica; 1991, 100, 2; 95-108
0039-3223
Pojawia się w:
Studia Mathematica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Almost everywhere summability of Laguerre series. II
Autorzy:
Stempak, K.
Powiązania:
https://bibliotekanauki.pl/articles/1293043.pdf
Data publikacji:
1992
Wydawca:
Polska Akademia Nauk. Instytut Matematyczny PAN
Tematy:
Laguerre expansions
Cesàro means
almost everywhere convergence
Opis:
Using methods from [9] we prove the almost everywhere convergence of the Cesàro means of Laguerre series associated with the system of Laguerre functions $L^a_n(x) = (n!/Γ(n+a+1))^{1/2} e^{-x/2} x^{a/2} L_n^a(x)$, n = 0,1,2,..., a ≥ 0. The novel ingredient we add to our previous technique is the $A_p$ weights theory. We also take the opportunity to comment and slightly improve on our results from [9].
Źródło:
Studia Mathematica; 1992, 103, 3; 317-327
0039-3223
Pojawia się w:
Studia Mathematica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
On the uniform convergence and L¹-convergence of double Walsh-Fourier series
Autorzy:
Móricz, Ferenc
Powiązania:
https://bibliotekanauki.pl/articles/1293178.pdf
Data publikacji:
1992
Wydawca:
Polska Akademia Nauk. Instytut Matematyczny PAN
Tematy:
Walsh-Paley system
W-continuity
moduli of continuity and smoothness
bounded variation in the sense of Hardy and Krause
generalized bounded variation
complementary functions in the sense of W. H. Young
rectangular partial sum
Dirichlet kernel
convergence in $L^p$-norm
uniform convergence Salem's test
Dini-Lipschitz test
Dirichlet-Jordan test
Opis:
In 1970 C. W. Onneweer formulated a sufficient condition for a periodic W-continuous function to have a Walsh-Fourier series which converges uniformly to the function. In this paper we extend his results from single to double Walsh-Fourier series in a more general setting. We study the convergence of rectangular partial sums in $L^p$-norm for some 1 ≤ p ≤ ∞ over the unit square [0,1) × [0,1). In case p = ∞, by $L^p$ we mean $C_W$, the collection of uniformly W-continuous functions f(x, y), endowed with the supremum norm. As special cases, we obtain the extensions of the Dini-Lipschitz test and the Dirichlet-Jordan test for double Walsh-Fourier series.
Źródło:
Studia Mathematica; 1992, 102, 3; 225-237
0039-3223
Pojawia się w:
Studia Mathematica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
A contribution to the topological classification of the spaces Ср(X)
Autorzy:
Cauty, Robert
Dobrowolski, Tadeusz
Marciszewski, Witold
Powiązania:
https://bibliotekanauki.pl/articles/1208632.pdf
Data publikacji:
1993
Wydawca:
Polska Akademia Nauk. Instytut Matematyczny PAN
Tematy:
function space
pointwise convergence topology
absorbing sets
Borel and projective filters
Opis:
We prove that for each countably infinite, regular space X such that $C_p(X)$ is a $Z_σ$-space, the topology of $C_p(X)$ is determined by the class $F_0(C_p(X))$ of spaces embeddable onto closed subsets of $C_p(X)$. We show that $C_p(X)$, whenever Borel, is of an exact multiplicative class; it is homeomorphic to the absorbing set $Ω_α$ for the multiplicative Borel class $M_α$ if $F_0(C_p(X)) = M_α$. For each ordinal α ≥ 2, we provide an example $X_α$ such that $C_p(X_α)$ is homeomorphic to $Ω_α$.
Źródło:
Fundamenta Mathematicae; 1993, 142, 3; 269-301
0016-2736
Pojawia się w:
Fundamenta Mathematicae
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
An inverse Sidon type inequality
Autorzy:
Fridli, S.
Powiązania:
https://bibliotekanauki.pl/articles/1292682.pdf
Data publikacji:
1993
Wydawca:
Polska Akademia Nauk. Instytut Matematyczny PAN
Tematy:
Sidon type inequalities
Hardy spaces
convergence classes
Opis:
Sidon proved the inequality named after him in 1939. It is an upper estimate for the integral norm of a linear combination of trigonometric Dirichlet kernels expressed in terms of the coefficients. Since the estimate has many applications for instance in $L^1$ convergence problems and summation methods with respect to trigonometric series, newer and newer improvements of the original inequality has been proved by several authors. Most of them are invariant with respect to the rearrangement of the coefficients. Although the newest results are close to best possible, no nontrivial lower estimate has been given so far. The aim of this paper is to give the best rearrangement invariant function of coefficients that can be used in a Sidon type inequality. We also show that it is equivalent to an Orlicz type and a Hardy type norm. Examples of applications are also given.
Źródło:
Studia Mathematica; 1993, 105, 3; 283-308
0039-3223
Pojawia się w:
Studia Mathematica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Convergence of iterates of asymptotically nonexpansive mappings in Banach spaces with the uniform Opial property
Autorzy:
Bruck, Ronald
Kuczumow, Tadeusz
Reich, Simeon
Powiązania:
https://bibliotekanauki.pl/articles/967351.pdf
Data publikacji:
1993
Wydawca:
Polska Akademia Nauk. Instytut Matematyczny PAN
Tematy:
convergence of iterates
uniform Opial property
asymptotically nonexpansive mapping
Źródło:
Colloquium Mathematicum; 1993, 65, 2; 169-179
0010-1354
Pojawia się w:
Colloquium Mathematicum
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Summable families in nuclear groups
Autorzy:
Banaszczyk, Wojciech
Powiązania:
https://bibliotekanauki.pl/articles/1292681.pdf
Data publikacji:
1993
Wydawca:
Polska Akademia Nauk. Instytut Matematyczny PAN
Tematy:
nuclear groups
unconditional and absolute convergence
Opis:
Nuclear groups form a class of abelian topological groups which contains LCA groups and nuclear locally convex spaces, and is closed with respect to certain natural operations. In nuclear locally convex spaces, weakly summable families are strongly summable, and strongly summable are absolutely summable. It is shown that these theorems can be generalized in a natural way to nuclear groups.
Źródło:
Studia Mathematica; 1993, 105, 3; 271-282
0039-3223
Pojawia się w:
Studia Mathematica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Unconditional ideals in Banach spaces
Autorzy:
Godefroy, G.
Kalton, N.
Saphar, P.
Powiązania:
https://bibliotekanauki.pl/articles/1292973.pdf
Data publikacji:
1993
Wydawca:
Polska Akademia Nauk. Instytut Matematyczny PAN
Tematy:
M-ideal
hermitian operator
unconditional convergence
Opis:
We show that a Banach space with separable dual can be renormed to satisfy hereditarily an "almost" optimal uniform smoothness condition. The optimal condition occurs when the canonical decomposition $X*** = X^{⊥} ⊕ X*$ is unconditional. Motivated by this result, we define a subspace X of a Banach space Y to be an h-ideal (resp. a u-ideal) if there is an hermitian projection P (resp. a projection P with ∥I-2P∥ = 1) on Y* with kernel $X^{⊥}$. We undertake a general study of h-ideals and u-ideals. For example we show that if a separable Banach space X is an h-ideal in X** then X has the complex form of Pełczyński's property (u) with constant one and the Baire-one functions Ba(X) in X** are complemented by an hermitian projection; the converse holds under a compatibility condition which is shown to be necessary. We relate these ideas to the more familiar notion of an M-ideal, and to Banach lattices. We further investigate when, for a separable Banach space X, the ideal of compact operators K(X) is a u-ideal or an h-ideal in ℒ(X) or K(X)**. For example, we show that K(X) is an h-ideal in K(X)** if and only if X has the "unconditional compact approximation property" and X is an M-ideal in X**.
Źródło:
Studia Mathematica; 1993, 104, 1; 13-59
0039-3223
Pojawia się w:
Studia Mathematica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Almost everywhere convergence of Laguerre series
Autorzy:
Chen, Chang-Pao
Lin, Chin-Cheng
Powiązania:
https://bibliotekanauki.pl/articles/1290468.pdf
Data publikacji:
1994
Wydawca:
Polska Akademia Nauk. Instytut Matematyczny PAN
Tematy:
almost everywhere convergence
Cesàro means
Laguerre polynomials
Riesz means
Opis:
Let $a ∈ ℤ^+$ and $f ∈ L^p (ℝ^+), 1 ≤ p ≤ ∞ $. Denote by $c_j$ the inner product of f and the Laguerre function $ℒ^a_j$. We prove that if ${c_j}$ satisfies $lim_{λ↓1} \overline lim_{n→∞} ∑_{n
Źródło:
Studia Mathematica; 1994, 109, 3; 291-301
0039-3223
Pojawia się w:
Studia Mathematica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Tauberian theorems for Cesàro summable double sequences
Autorzy:
Móricz, Ferenc
Powiązania:
https://bibliotekanauki.pl/articles/1290321.pdf
Data publikacji:
1994
Wydawca:
Polska Akademia Nauk. Instytut Matematyczny PAN
Tematy:
double sequence
convergence in Pringsheim's sense
summability (C,1,1)
(C,1,0) and (C,0,1)
one-sided Tauberian condition of Landau and Hardy type
slow decrease
ordered linear space
Opis:
$(s_{jk}: j,k = 0,1,...)$ be a double sequence of real numbers which is summable (C,1,1) to a finite limit. We give necessary and sufficient conditions under which $(s_{jk})$ converges in Pringsheim's sense. These conditions are satisfied if $(s_{jk})$ is slowly decreasing in certain senses defined in this paper. Among other things we deduce the following Tauberian theorem of Landau and Hardy type: If $(s_{jk})$ is summable (C,1,1) to a finite limit and there exist constants $n_1 > 0$ and H such that $jk(s_{jk} - s_{j-1,k} - s_{j-1,k} + s_{j-1,k-1}) ≥ -H$, $j(s_{jk} - s_{j-1, k}) ≥ -H$ and $k(s_{jk} - s_{j,k-1}) ≥ -H$ whenever $j,k > n_1$, then $(s_{jk})$ converges. We always mean convergence in Pringsheim's sense. Our method is suitable to obtain analogous Tauberian results for double sequences of complex numbers or for those in an ordered linear space over the real numbers.
Źródło:
Studia Mathematica; 1994, 110, 1; 83-96
0039-3223
Pojawia się w:
Studia Mathematica
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-15 z 604

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