Базисы из экспонент в пространствахL p

Let the rootsλ _n of an entire functionL(z) be separated and lie in some horizontal strip ¦Im z¦ ≦h, and suppose that $$0< c \leqq |L(z)|(1 + |z|)^{ - b} \exp ( - a|\operatorname{Im} z|) \leqq C< \infty$$ for ¦Imz¦≧H>h. If 1<p<2 and - 1/pq (1/q+1/p=1), then the system {exp (iλ _n x)} _n=0 ^∞ constitutes a basis нn the spaceL ^p (-a,a). In the caseb=1/q orb=?1/p the theorem fails, Equivalence of the following two statements is also proved:

1. {exp (iλ _n x)} _n=0 ^∞ is an extendable convergence system inL ^p from the interval (-a, a).
2. {exp (iλ _n x)} _n=0 ^∞ is a continuable basis inL ^p (-a,a).

     

Subspaces of L p that embed into L p (µ) with µ finite

Enflo and Rosenthal [4] proved that ? _p (?₁), 1 < p < 2, does not (isomorphically) embed into L _p (µ) with µ a finite measure. We prove that if X is a subspace of an L _p space, 1 < p < 2, and ? _p (?₁) does not embed into X, then X embeds into L _p (µ) for some finite measure µ.     

ОптИМАльНыЕ кВАДРАт УРНыЕ ФОРМУлы Дль клА ссОВ ФУНкцИИ с ИНтЕгРИРУЕ МОИ ВL p r-ОИ пРОИжВОДНОИ

On the classW ^r L _p (1≦p≦∞;r=1, 2,…) of 1-periodic functions ?(x) having an absolutely continuous (r? l)st derivative such that $$\parallel f^{(r)} \parallel _{L_p } \leqq 1 (\parallel f^{(r)} \parallel _{L_\infty } = vrai \sup |f^{(r)} (x)|)$$ vrai sup ¦?(^r)(x)¦) an optimal quadrature formula of the form (0 ≦? ≦r?1, 0 ≦x ₀ < x₁ <…< x_m ≦ 1) is found in the cases ?=r?2 and ?=r? 3 (r=3, 5, …). An exact error bound is established for this formula. The statements proved forW ^r L _p allowed us also to obtain, under certain restrictions posed on the coefficientsp _kl, and the nodesx ₀ andx _m, optimal quadrature formulae for the classes $$W_0^r L_p = \{ f:f \in W^r L_p , f^{(i)} (0) = 0 (i = 0,1,...,r - 2)\} $$ and $$W_0^r L_p = \{ f:f \in \tilde W^r L_p , f^{(i)} (0) = f^{(i)} (1) = 0 (i = 0,1,...,r - 2)\} $$ for the same values ofp andr as above.     

Оценки отклонений оп тимальных сеток вL p -норме и теория квад ратурных формул

Let E^s=[0, 1]^s be then-dimensional unit cube, 1<p<∞, anda=(a ₁, ...,a _s ) some set of natural numbers. Denote byL _p ^(a) , (E ^s ) the class of functionsf: E ^s → C for which $$\left\| {\frac{{\partial ^{b_1 + \cdots + b_s } f}}{{\partial x_1^{b_1 } \cdots \partial x_s^{b_s } }}} \right\|_p \leqslant 1,$$ where $$0< b_1< a_1 , ..., 0< b_s< a_s .$$ Set $$R_p^{\left( a \right)} \left( N \right) = \mathop {\inf }\limits_{card \mathfrak{S} = N} R_\mathfrak{S} \left( {L_p^{\left( a \right)} \left( {E^s } \right)} \right),$$ where $R_\mathfrak{S} \left( {L_p^{\left( a \right)} \left( {E^s } \right)} \right)$ is the error of the quadrature formulas on the mesh $\mathfrak{S}$ (for the classL _p ^(a) (E ^s )), consisting of N nodes and weights, and the infimum is taken with respect to all possibleN nodes and weights. In this paper, the two-sided estimate $$\frac{{\left( {\log N} \right)^{{{\left( {l - 1} \right)} \mathord{\left/ {\vphantom {{\left( {l - 1} \right)} 2}} \right. \kern-\nulldelimiterspace} 2}} }}{{N^d }} \ll _{p, a} R^{\left( a \right)} \left( N \right) \ll _{p, a} \frac{{\left( {\log N} \right)^{{{\left( {l - 1} \right)} \mathord{\left/ {\vphantom {{\left( {l - 1} \right)} 2}} \right. \kern-\nulldelimiterspace} 2}} }}{{N^d }}$$ is proved for every natural numberN > 1, whered=min{a ₁, ...,a _s }, whilel is the number of those components of a which coincide withd. An analogous result is proved for theL _p -norm of the deviation of meshes.     

Affine Synthesis onto L p when 0<p≤1

The affine synthesis operator is shown to map the coefficient space ℓ ^p (ℤ₊×ℤ ^d ) surjectively onto L ^p (ℝ ^d ), for p∈(0,1]. Here ψ _j,k (x)=|det a _j |^1/p ψ(a _j x−k) for dilation matrices a _j that expand, and the synthesizer ψ∈L ^p (ℝ ^d ) need satisfy only mild restrictions, for example, ψ∈L ¹(ℝ ^d ) with nonzero integral or else with periodization that is real-valued, nontrivial and bounded below. An affine atomic decomposition of L ^p follows immediately:

N-widths of Ω r ′ in L p

Let Ω _ϕ ^r ={f:f ^(r-1) abs. cont. on [0,1], ‖q_r(D)f‖_p≤1, f^(2K+σ) (0)=f^(2K+σ)=0, (k)=0,...,l-1}. where , and I is an identical operator. Denote Kolmogorov, linear, Geelfand and Bernstein n-widths of Ω _ϕ ^r in L^p byd _n (Ω _ϕ ^r ;L ^p ),δ _n (Ω _ϕ ^r ;L ^p ),d ⁿ (Ω _p ^r ;L ^p ) andb _n (Ω _p ^r ;L ^p ), respectively. In this paper, we find a method to get an exact estimation of these n-widths. Related optimal subspaces and an optimal linear operator are given. For another subset , similar results are also derrived.     

О мультипликативном дополнении некоторы х неполных ортонормированных с истем до базисов вL p , 1≦p<∞

The problem of the possibility of multiplicative completion to basis for the sequence of functions which arise after the deletion of a finite collection of elements from a complete orthonormal system of functions is solved.For some complete orthonormal systems (for instance the Walsh system, the trigonometric system etc.) there exists no such measurable function.On the other hand, if any finite collection of functions is deleted from the Haar system, there exists a bounded function such that after multiplying the remaining set of functions by this function the system obtained will be a basis in all spacesL ^p , 1p<.For the Haar system certain infinite deletions are also possible.

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L p uncertainty principles on Sturm–Liouville hypergroups

We use the Fourier analysis associated to a singular second-order differential operator Δ, and prove a continuous-time principle for the L ^p theory.     

L p -spectral estimation with anL ∞-upper bound

Given the constraint 0≤f≤B, whereB is in the interior of the positive cone ofL _∞, and given a finite number of correlations off, we wish to estimatef. Since only a finite number of correlations are given, this does not uniquely determinef. We estimatef by picking the unique function Φ₀ satisfying the constraints and minimizing theL _p -norm with 1<p<∞. Under suitable conditions, the form of the solution is shown to be $$\Phi _0 (f) = \min \{ B(x), \max \{ 0,P(x)\} ^{1/(p - 1)} \} ,$$ whereP is a linear combination of the correlation functions.     

A Jackson Type Estimate for Shepard Operators in L p Spaces for p≧ 1

This paper considers the approximation of the Kantorovich–Shepard operators in spaces for . For the Kantorovich–Shepard operators are defined by (1.1). Then

(L p –L q )-boundedness of pseudodifferential operators on the n-dimensional torus

Mathematical Notes -     

Narrow and ℓ2-strictly singular operators from L p

In the first part of the paper we prove that for 2 < p, r < ∞ every operator T: L _p → ? _r is narrow. This completes the list of sequence and function Lebesgue spaces X with the property that every operator T : L _p → X is narrow. Next, using similar methods we prove that every ?₂-strictly singular operator from L _p , 1 < p < ∞, to any Banach space with an unconditional basis, is narrow, which partially answers a question of Plichko and Popov posed in 1990. A theorem of H. P. Rosenthal asserts that if an operator T from L ₁[0, 1] to itself satisfies the assumption that for each measurable set A ? [0, 1] the restriction \(T{|_{{L_1}(A)}}\) is not an isomorphic embedding, then T is narrow. (Here L ₁(A) = {x ∈ L ₁ : supp x ? A}.) Inspired by this result, in the last part of the paper, we find a sufficient condition, of a different flavor than being ?₂-strictly singular, for operators from L _p [0, 1] to itself, 1 < p < 2, to be narrow. We define a notion of a “gentle” growth of a function and we prove that for 1 < p < 2 every operator T from L _p to itself which, for every A ? [0, 1], sends a function of “gentle” growth supported on A to a function of arbitrarily small norm is narrow.     

Unconditional structures of translates for L p (ℝ d )

We prove that a sequence (f _i ) _i=1 ^∞ of translates of a fixed f ∈ L _p (?) cannot be an unconditional basis of L _p (?) for any 1 ≤ p < ∞. In contrast to this, for every 2 < p < ∞, d ∈ ? and unbounded sequence (λ _n ) _n∈? ? ? ^d we establish the existence of a function f ∈ L _p (? ^d ) and sequence (g _n *) _n∈? ? L _p *(? ^d ) such that \({({T_{{\lambda _n}}}f,g_n^*)_{n \in {\Bbb N}}}\) forms an unconditional Schauder frame for L _p (? ^d ). In particular, there exists a Schauder frame of integer translates for L _p (?) if (and only if) 2 < p < ∞.     

On the spaces C k (ℝ) ∩ L p (ℝ)

We show that the Fréchet-Sobolev spaces C(ℝ) ∩ L ^p (ℝ) and C ^k (ℝ) ∩ L ^p (ℝ) are not isomorphic for p ≠ 2 and k ∈ ℕ. Research supported by the Italian MURST.     

An extension of Mercer’s theory to L p

Let X be a topological space, either locally compact or first countable, endowed with a strictly positive measure ?? and ${\mathcal{K}:L^2(X,\nu)\to L^2(X,\nu)}$ an integral operator generated by a Mercer like kernel K. In this paper we extend Mercer??s theory for K and ${\mathcal{K}}$ under the assumption that the function ${x\in X\to K(x,x)}$ belongs to some L ^p/2(X, ??), p??? 1. In particular, we obtain series representations for K and some powers of ${\mathcal{K}}$ , with convergence in the p-mean, and show that the range of certain powers of ${\mathcal{K}}$ contains continuous functions only. These results are used to estimate the approximation numbers of a modified version of ${\mathcal{K}}$ acting on L ^p (X, ??).     

Daugavet type inequalities for operators on L p–spaces

Let T be a regular operator from L ^p L ^p. Then , where T_r denotes the regular norm of T, i.e., T_r=|T| where |T| denotes the modulus operator of a regular operator T. For p=1 every bounded linear operator is regular and T=T_r, so that the above inequality generalizes the Daugavet equation for operators on L ¹–spaces. The main result of this paper (Theorem 9) is a converse of the above result. Let T be a regular linear operator on L _p and denote by T _A the operator T_A. Then for all A with (A)>0 if and only if .     

The divergence equation in weighted- and L p(��)-spaces

We study the solvability of the divergence equation in weighted spaces and Lebesgue spaces with variable exponents, where the weights are so called Muckenhoupt weights. The question of constructing divergence free test functions, which can be used for problems arising in fluid dynamics, is also addressed. The approach is based on an explicit representation formula for solutions of the divergence equation due to Bogovski? and the theory of singular integral operators. The developed methods are used to prove an existence result for fluids which satisfy a p(·)-growth condition.     

不动点集为L1(p)的对合

§ 1.　Introduction　　Let(M ,T)beasmoothinvolutiononasmoothclosedmanifold ,andFdenotesthefixedpointsetof (M ,T) .WhenF =RP( 2k) ,RP(m)∪RP(n) ,∪RP( 2l+ 1 ) (lfixed) ,∪pi =1 RP( 2li+ 1 ) ,∪ri =1 (S1 ) ki ,(Sn1 ×Sn2 ×… ×Snp)∪ {pt},etc .,theexistenceandtherepresentative (uptobordism)of(M ,T)havebeenstudiedin [2 ],[3],[5 ],[6],[7]and[8].Thepurposeofthepaperistodeterminetheexistenceandtherepretentativeuptobord ismofallinvolutionsfixingthelensspaceL1 ( p) ,whereL1 ( p)isa 3 dimens…     

Global L p estimates for degenerate Ornstein–Uhlenbeck operators

We consider a class of degenerate Ornstein–Uhlenbeck operators in ${\mathbb{R}^{N}}We consider a class of degenerate Ornstein–Uhlenbeck operators in \mathbbR^N{\mathbb{R}^{N}} , of the kind

A o ?i, j=1p0aij?xixj2 + ?i, j=1Nbijxi?xj\mathcal{A}\equiv\sum_{i, j=1}^{p_{0}}a_{ij}\partial_{x_{i}x_{j}}^{2} + \sum_{i, j=1}^{N}b_{ij}x_{i}\partial_{x_{j}}