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Search: All articles in the CMB digital archive with keyword convergence

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1. CMB Online first

Xu, Xu; Zhu, Laiyi
Rational function operators from Poisson integrals
In this paper, we construct two classes of rational function operators by using the Poisson integrals of the function on the whole real axis. The convergence rates of the uniform and mean approximation of such rational function operators on the whole real axis are studied.

Keywords:rational function operators, Poisson integrals, convergence rate, uniform approximation, mean approximation
Categories:41A20, 41A25, 41A35

2. CMB 2014 (vol 57 pp. 708)

Brannan, Michael
Strong Asymptotic Freeness for Free Orthogonal Quantum Groups
It is known that the normalized standard generators of the free orthogonal quantum group $O_N^+$ converge in distribution to a free semicircular system as $N \to \infty$. In this note, we substantially improve this convergence result by proving that, in addition to distributional convergence, the operator norm of any non-commutative polynomial in the normalized standard generators of $O_N^+$ converges as $N \to \infty$ to the operator norm of the corresponding non-commutative polynomial in a standard free semicircular system. Analogous strong convergence results are obtained for the generators of free unitary quantum groups. As applications of these results, we obtain a matrix-coefficient version of our strong convergence theorem, and we recover a well known $L^2$-$L^\infty$ norm equivalence for non-commutative polynomials in free semicircular systems.

Keywords:quantum groups, free probability, asymptotic free independence, strong convergence, property of rapid decay
Categories:46L54, 20G42, 46L65

3. CMB 2012 (vol 56 pp. 544)

Gauthier, P. M.
Universally Overconvergent Power Series via the Riemann Zeta-function
The Riemann zeta-function is employed to generate universally overconvergent power series.

Keywords:overconvergence, zeta-function
Categories:30K05, 11M06

4. CMB 2011 (vol 55 pp. 242)

Cegrell, Urban
Convergence in Capacity
In this note we study the convergence of sequences of Monge-Ampère measures $\{(dd^cu_s)^n\}$, where $\{u_s\}$ is a given sequence of plurisubharmonic functions, converging in capacity.

Keywords:complex Monge-Ampère operator, convergence in capacity, plurisubharmonic function
Categories:32U20, 31C15

5. CMB 2011 (vol 55 pp. 424)

Yang, Jianbin; Li, Song
Convergence Rates of Cascade Algorithms with Infinitely Supported Masks
We investigate the solutions of refinement equations of the form $$ \phi(x)=\sum_{\alpha\in\mathbb Z^s}a(\alpha)\:\phi(Mx-\alpha), $$ where the function $\phi$ is in $L_p(\mathbb R^s)$$(1\le p\le\infty)$, $a$ is an infinitely supported sequence on $\mathbb Z^s$ called a refinement mask, and $M$ is an $s\times s$ integer matrix such that $\lim_{n\to\infty}M^{-n}=0$. Associated with the mask $a$ and $M$ is a linear operator $Q_{a,M}$ defined on $L_p(\mathbb R^s)$ by $Q_{a,M} \phi_0:=\sum_{\alpha\in\mathbb Z^s}a(\alpha)\phi_0(M\cdot-\alpha)$. Main results of this paper are related to the convergence rates of $(Q_{a,M}^n \phi_0)_{n=1,2,\dots}$ in $L_p(\mathbb R^s)$ with mask $a$ being infinitely supported. It is proved that under some appropriate conditions on the initial function $\phi_0$, $Q_{a,M}^n \phi_0$ converges in $L_p(\mathbb R^s)$ with an exponential rate.

Keywords:refinement equations, infinitely supported mask, cascade algorithms, rates of convergence
Categories:39B12, 41A25, 42C40

6. CMB 2011 (vol 55 pp. 15)

Akiyama, Shigeki; Suzuki, Tomonari
Browder's Convergence for One-Parameter Nonexpansive Semigroups
We give the sufficient and necessary conditions of Browder's convergence theorem for one-parameter nonexpansive semigroups which was proved by Suzuki. We also discuss the perfect kernels of topological spaces.

Keywords:nonexpansive semigroup, common fixed point, Browder's convergence, perfect kernel

7. CMB 2011 (vol 54 pp. 566)

Zhou, Xiang-Jun; Shi, Lei; Zhou, Ding-Xuan
Non-uniform Randomized Sampling for Multivariate Approximation by High Order Parzen Windows
We consider approximation of multivariate functions in Sobolev spaces by high order Parzen windows in a non-uniform sampling setting. Sampling points are neither i.i.d. nor regular, but are noised from regular grids by non-uniform shifts of a probability density function. Sample function values at sampling points are drawn according to probability measures with expected values being values of the approximated function. The approximation orders are estimated by means of regularity of the approximated function, the density function, and the order of the Parzen windows, under suitable choices of the scaling parameter.

Keywords:multivariate approximation, Sobolev spaces, non-uniform randomized sampling, high order Parzen windows, convergence rates
Categories:68T05, 62J02

8. CMB 2010 (vol 53 pp. 503)

Kurenok, V. P.
The Time Change Method and SDEs with Nonnegative Drift
Using the time change method we show how to construct a solution to the stochastic equation $dX_t=b(X_{t-})dZ_t+a(X_t)dt$ with a nonnegative drift $a$ provided there exists a solution to the auxililary equation $dL_t=[a^{-1/\alpha}b](L_{t-})d\bar Z_t+dt$ where $Z, \bar Z$ are two symmetric stable processes of the same index $\alpha\in(0,2]$. This approach allows us to prove the existence of solutions for both stochastic equations for the values $0<\alpha<1$ and only measurable coefficients $a$ and $b$ satisfying some conditions of boundedness. The existence proof for the auxililary equation uses the method of integral estimates in the sense of Krylov.

Keywords:One-dimensional SDEs, symmetric stable processes, nonnegative drift, time change, integral estimates, weak convergence
Categories:60H10, 60J60, 60J65, 60G44

9. CMB 2009 (vol 52 pp. 627)

Yu, Dan Sheng; Zhou, Ping; Zhou, Song Ping
On $L^{1}$-Convergence of Fourier Series under the MVBV Condition
Let $f\in L_{2\pi }$ be a real-valued even function with its Fourier series $% \frac{a_{0}}{2}+\sum_{n=1}^{\infty }a_{n}\cos nx,$ and let $S_{n}(f,x) ,\;n\geq 1,$ be the $n$-th partial sum of the Fourier series. It is well known that if the nonnegative sequence $\{a_{n}\}$ is decreasing and $\lim_{n\rightarrow \infty }a_{n}=0$, then% \begin{equation*} \lim_{n\rightarrow \infty }\Vert f-S_{n}(f)\Vert _{L}=0 \text{ if and only if }\lim_{n\rightarrow \infty }a_{n}\log n=0. \end{equation*}% We weaken the monotone condition in this classical result to the so-called mean value bounded variation (MVBV) condition. The generalization of the above classical result in real-valued function space is presented as a special case of the main result in this paper, which gives the $L^{1}$% -convergence of a function $f\in L_{2\pi }$ in complex space. We also give results on $L^{1}$-approximation of a function $f\in L_{2\pi }$ under the MVBV condition.

Keywords:complex trigonometric series, $L^{1}$ convergence, monotonicity, mean value bounded variation
Categories:42A25, 41A50

10. CMB 2009 (vol 52 pp. 315)

Yi, Taishan; Zou, Xingfu
Generic Quasi-Convergence for Essentially Strongly Order-Preserving Semiflows
By employing the limit set dichotomy for essentially strongly order-preserving semiflows and the assumption that limit sets have infima and suprema in the state space, we prove a generic quasi-convergence principle implying the existence of an open and dense set of stable quasi-convergent points. We also apply this generic quasi-convergence principle to a model for biochemical feedback in protein synthesis and obtain some results about the model which are of theoretical and realistic significance.

Keywords:Essentially strongly order-preserving semiflow, compactness, quasi-convergence
Categories:34C12, 34K25

11. CMB 2008 (vol 51 pp. 372)

Ezquerro, J. A.; Hernández, M. A.
Picard's Iterations for Integral Equations of Mixed Hammerstein Type
A new semilocal convergence result for the Picard method is presented, where the main required condition in the contraction mapping principle is relaxed.

Keywords:nonlinear equations in Banach spaces, successive approximations, semilocal convergence theorem, Picard's iteration, Hammerstein integral equations
Categories:45G10, 47H99, 65J15

12. CMB 2006 (vol 49 pp. 256)

Neelon, Tejinder
A Bernstein--Walsh Type Inequality and Applications
A Bernstein--Walsh type inequality for $C^{\infty }$ functions of several variables is derived, which then is applied to obtain analogs and generalizations of the following classical theorems: (1) Bochnak--Siciak theorem: a $C^{\infty }$\ function on $\mathbb{R}^{n}$ that is real analytic on every line is real analytic; (2) Zorn--Lelong theorem: if a double power series $F(x,y)$\ converges on a set of lines of positive capacity then $F(x,y)$\ is convergent; (3) Abhyankar--Moh--Sathaye theorem: the transfinite diameter of the convergence set of a divergent series is zero.

Keywords:Bernstein-Walsh inequality, convergence sets, analytic functions, ultradifferentiable functions, formal power series
Categories:32A05, 26E05

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