Geometric conditions for interpolation in weighted spaces of entire functions

We use L² estimates for the equation to find geometric conditions on discrete interpolating varieties for weighted spaces A_p(ℂ) of entire functions such that |f(z)|≤Ae^Bp(z) for some A, B>0. In particular, we give a characterization when p(z)=e^|z| and more generally, when In p(e^r) is convex andIn p(r) is concave. Acknowledgements and Notes. The author wishes to thank X. Massaneda for useful talks and remarks.     

Conjugate interpolation problems in spaces of entire functions

A generalization of the Taylor expansions of entire functions with variable center is used to illustrate the notion of conjugate interpolation problem. The radii of existence, uniqueness, and convergence for such problems are found. A relationship between the interpolation functional systems of two mutually conjugate problems is revealed. Translated fromMatematicheskie Zametki, Vol. 67, No. 4, pp. 616–628, April, 2000.     

Simultaneous approximation and interpolation of increasing functions by increasing entire functions

We prove that, under suitable assumptions, an isomorphism g of dense subsets A,B of the real line can be taken to approximate a given increasing Cⁿ surjection f with the derivatives of g agreeing with those of f on a closed discrete set. For example, we have the following theorem. Let be a nondecreasing Cⁿ surjection. Let be a positive continuous function. Let be a closed discrete set on which f is strictly increasing. Let each of {A_i}, {B_i} be a sequence of pairwise disjoint countable dense subsets of such that for each and xE we have xA_i if and only if f(x)B_i. Then there is an entire function such that and the following properties hold.

(a) For all , Dg(x)>0.

(b) For k=0,…,n and all , |D^kf(x)−D^kg(x)|<ε(x).

(c) For k=0,…,n and all xE, D^kf(x)=D^kg(x).

(d) For each , g[A_i]=B_i.

This provides a version for increasing functions of a theorem of Hoischen. In earlier work, we proved that it is consistent that a similar theorem, omitting clause (c), holds when the sets A_i,B_i are of cardinality ₁ and have second category intersection with every interval. (See the introduction for the exact statement.) In this paper, we show how to incorporate clause (c) into the statement of the earlier theorem.

Lacunary interpolation by quartic splines on uniform meshes

The interpolation of a discrete set of data on the interval [0, 1], representing the first and the second derivatives (except at 0) of a smooth function f is investigated via quartic C²-splines. Error bounds in the uniform norm for ∥s⁽ⁱ⁾ − f⁽ⁱ⁾∥, i=0(1)2, if f ∈ C^l[0, 1], l=3, 5 and ⁽³⁾ ∈ BV[0, 1], together with computational examples will also be presented.     

Sampling and interpolation of entire functions and exponential systems in convex domains

Research supported by the Norwegian Research Council for Science and Humanities (NAVF).     

On the trigonometric interpolation and the entire interpolation

In this paper, we study a kind of interpolation problems on a given nodal set by trigonometric polynomials of order n and entire functions of exponential type according as the nodal set is respectively. We established some equivalent conditions and found the explicit forms of some interpolation functions on the interpolation problems. As a special case, the explicit forms of fundamential functions of (0,m)-interpolat on by trigonometric case or entire functions case (in B² _σ) respectively, if they exist, may follow from our results. Besides, we also considered the convergence of the interpolation functions at above stated. Suported by the Natural Youth Science Foundation of Beijing Normal University.