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Interpolation by generalized exponential sums with equal weights
Journal of Approximation Theory ( IF 0.9 ) Pub Date : 2020-03-05 , DOI: 10.1016/j.jat.2020.105397
Petr Chunaev

In this paper we solve Padé (i.e. multiple) and Prony (i.e. simple exponential) interpolation problems for the generalized exponential sums with equal weights: Hn(z;h)μnk=1nh(λkz),whereμ,λk,and h is a fixed analytic function under few natural assumptions. The interpolation of a function f by Hn is due to properly chosen μ and {λk}k=1n, which depend on f, h and n. The sums Hn are related to the h-sums and amplitude and frequency sums (also known as generalized exponential sums), i.e. correspondingly to Hn(z;h)k=1nλkh(λkz)andHn(z;h)k=1nμkh(λkz),whereμk,λk,which generalize many classical approximants and whose properties are actively studied.

As for the Padé problem, we show that Hn and Hn have similar constructions and rates of interpolation, whereas calculating Hn requires less arithmetic operations. Although the Padé problem for Hn is known to have a doubled interpolation rate with respect to Hn and thus to Hn, it can be however unsolvable in quite simple and useful cases and this may entirely eliminate the advantage of Hn. We show that, in contrast to Hn, the Padé problem for Hn always has a unique solution. What is even more important, we also obtain several efficient estimates for μ and λk, valuable by themselves, and use them in further evaluating interpolation quality and in numerical applications.

The above-mentioned Padé problem and estimates provide a basis for managing the more interesting Prony problem for exponential sums with equal weights Hn(z;exp), i.e. when h(z)=exp(z). We show that it is uniquely solvable and surprisingly μ and λk can be efficiently estimated. This is in sharp contrast to the case of well-known exponential sums Hn(z;exp).



中文翻译:

权重相等的广义指数和的插值

在本文中,我们解决了权重相等广义指数和的Padé(即多次)和Prony(即简单指数)插值问题:Hñž;Hμñķ=1个ñHλķž哪里μλķH是在少数自然假设下的固定分析函数。函数的内插F 通过 Hñ 是由于正确选择 μ{λķ}ķ=1个ñ,取决于 FHñ。总和Hñ 与有关 H-和,幅度和频率和(也称为广义指数和),即对应于Hñž;Hķ=1个ñλķHλķžHñž;Hķ=1个ñμķHλķž哪里μķλķ归纳了许多经典近似值,并对其性质进行了积极研究。

关于Padé问题,我们证明 HñHñ 具有相似的构造和内插率,而计算 Hñ需要较少的算术运算。尽管Padé问题Hñ 已知相对于 Hñ 因此 Hñ,但是在非常简单和有用的情况下可能无法解决,并且这可能会完全消除 Hñ。我们证明,与Hñ,Padé问题 Hñ总是有独特的解决方案。更重要的是,我们还获得了一些有效的估计μλķ本身具有价值,并将其用于进一步评估插值质量和数值应用。

上述Padé问题和估计值为管理权重相等的指数和更有趣的Prony问题提供了基础 Hñž;经验值,即何时 Hž=经验值ž。我们证明它是唯一可解决的并且令人惊讶μλķ可以有效地估算。这与众所周知的指数和的情况形成鲜明对比 Hñž;经验值

更新日期:2020-03-05
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