Jackson theorem in Lp,0

F. Dai  Z. Ditzian 《Journal of Approximation Theory》2010,162(2):382-391

The multidimensional Luzin theorem

Each measurable map of an open set U⊂Rn to Rn is equal almost everywhere to the gradient of a continuous almost everywhere differentiable function defined on Rn that vanishes, together with its gradient, outside U.     

The Jackson theorem inB a spaces

As everyone knows, the classical Jackson theorem in approximation theory was generalized in L_p spaces by R. A. Devore^[4]. In this paper, we proved the Jackson theorem in B_a spaces which introduced by Ding Xia Xi.     

On a theorem of Jackson

We prove that $$\mathop {L_n \in Z_n }\limits^{\inf } \mathop \omega \limits^{sup^* } \mathop {f \in H_\omega }\limits^{\sup } \frac{{\left\| {f - L_n \left( f \right)} \right\|}}{{\omega \left( {\frac{\pi }{{n + 1}}} \right)}} = 1\left( {n = 0,1,2,...} \right)$$ (n=0,1,2,...), where \(\mathop {L_n \in Z_n }\limits^{\inf } \) is taken over all linear polynomial approximation methods of degree not higher than n and \(\mathop \omega \limits^{sup^* } \) over all convex moduli of continuity ω(δ).     

The Jackson theorem inL 2 for Christenson-Levy systems

Translated from Matematicheskie Zametki, Vol., 53, No. 4, pp. 111–130, April, 1993.     

Lp theory for the multidimensional aggregation equation

We consider well‐posedness of the aggregation equation ∂_tu + div(uv) = 0, v = −▿K * u with initial data in \input amssym ${\cal P}_2 {\rm (\Bbb R}^d {\rm )} \cap L^p ({\Bbb R}^d )$ in dimensions 2 and higher. We consider radially symmetric kernels where the singularity at the origin is of order |x|^α, α > 2 − d, and prove local well‐posedness in \input amssym ${\cal P}_2 { (\Bbb R}^d {\rm )} \cap L^p ({\Bbb R}^d )$ for sufficiently large p < p_s. In the special case of K(x) = |x|, the exponent p_s = d/(d = 1) is sharp for local well‐posedness in that solutions can instantaneously concentrate mass for initial data in \input amssym ${\cal P}_2 { (\Bbb R}^d {\rm )} \cap L^p ({\Bbb R}^d )$ with p < p_s. We also give an Osgood condition on the potential K(x) that guarantees global existence and uniqueness in \input amssym ${\cal P}_2 { (\Bbb R}^d {\rm )} \cap L^p ({\Bbb R}^d )$ . © 2010 Wiley Periodicals, Inc.     

推广Jackson逼近阶定理

在随机函数的环境下,推广了经典函数逼近论中的Jackson逼近阶定理.建立了随机函数均方连续模的概念,并得到其有关性质后,研究了四种不同条件下随机函数被随机系数三角多项式逼近的阶之估计.     

Multidimensional Jackson theorem in the L2 SPACE

Translated from Matematicheskie Zametki, Vol. 49, No. 5, pp. 154–156, May, 1991.     

JACKSON‘S THEOREM FOR COMPACT GROUPS

In this article we consider the generalized shift operator defined by (Shuf)(g)=∫Gf(tut^-1g)dt on compact group G and by help of this operator we define “Spherical” modulus of continuity.So we prove Stechkin and Jackson type theorems.     

Birkhoff's theorem and multidimensional numerical range

We show that, under certain conditions, Birkhoff's theorem on doubly stochastic matrices remains valid for countable families of discrete probability spaces which have nonempty intersections. Using this result, we study the relation between the spectrum of a self-adjoint operator A and its multidimensional numerical range. It turns out that the multidimensional numerical range is a convex set whose extreme points are sequences of eigenvalues of the operator A. Every collection of eigenvalues which can be obtained by the Rayleigh-Ritz formula generates an extreme point of the multidimensional numerical range. However, it may also have other extreme points.     

The monotone convergence theorem for multidimensional abstract Kurzweil vector integrals

We prove two versions of the Monotone Convergence Theorem for the vector integral of Kurzweil, , where R is a compact interval of , and f are functions with values on L(Z,W) and Z respectively, and Z and W are monotone ordered normed spaces. Analogous results can be obtained for the Kurzweil vector integral, , as well as to unbounded intervals R.     

L^p与△^p空间的小波逼近定理

定义了线性小波算子序列,运用其概率性质研究其对Lp与△^p空间函数的逼近性质,建立了相应的逼近等价定理。