论文标题

在Chebyshev节点的过滤多项式插值上

On the filtered polynomial interpolation at Chebyshev nodes

论文作者

Occorsio, Donatella, Themistoclakis, Woula

论文摘要

该论文处理了一种特殊的过滤近似方法,该方法通过使用delaValléePoussin滤镜来源于Chebyshev零的插值多项​​式。这些多项式可以是许多理论和应用问题的有用装置,因为它们结合了经典的Lagrange插值的优势,并在配备有适当的Jacobi - Wepter-Weighted,均匀统一规范的本地连续功能的空间中均匀收敛。相关的Lebesgue常数的统一界限等于统一的融合,而在拉格朗日插值中缺失,在不同但仅充分的假设下的文献中已经证明了这一点。在这里,我们指出获得它的必要条件。这些条件很容易检查,因为它们对定义标准的Jacobi重量的指数很简单。此外,它们是必要和足够的,足以获得几乎最佳近似误差的过滤插值多项式,这往往为零,因为数量$ n $ nodes倾向于无穷大。另外,收敛速率与度$ n $的最佳多项式近似的误差相当,因此近似顺序随着寻求函数的平滑度而提高。为了测试理论结果,进行了几个数值实验,以与同一节点的拉格朗日插值进行比较,并显示如何大大降低吉布斯现象。

The paper deals with a special filtered approximation method, which originates interpolation polynomials at Chebyshev zeros by using de la Vallée Poussin filters. These polynomials can be an useful device for many theoretical and applicative problems since they combine the advantages of the classical Lagrange interpolation, with the uniform convergence in spaces of locally continuous functions equipped with suitable, Jacobi--weighted, uniform norms. The uniform boundedness of the related Lebesgue constants, which equals to the uniform convergence and is missing from Lagrange interpolation, has been already proved in literature under different, but only sufficient, assumptions. Here, we state the necessary and sufficient conditions to get it. These conditions are easy to check since they are simple inequalities on the exponents of the Jacobi weight defining the norm. Moreover, they are necessary and sufficient to get filtered interpolating polynomials with a near best approximation error, which tends to zero as the number $n$ of nodes tends to infinity. In addition, the convergence rate is comparable with the error of best polynomial approximation of degree $n$, hence the approximation order improves with the smoothness of the sought function. Several numerical experiments are given in order to test the theoretical results, to make a comparison with the Lagrange interpolation at the same nodes and to show how the Gibbs phenomenon can be strongly reduced.

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