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Negative results in coconvex approximation of periodic functions
Journal of Approximation Theory ( IF 0.9 ) Pub Date : 2021-04-20 , DOI: 10.1016/j.jat.2021.105582 German Dzyubenko , Victoria Voloshyna , Lyudmyla Yushchenko
中文翻译:
周期函数协凸近似的负结果
更新日期:2021-04-23
Journal of Approximation Theory ( IF 0.9 ) Pub Date : 2021-04-20 , DOI: 10.1016/j.jat.2021.105582 German Dzyubenko , Victoria Voloshyna , Lyudmyla Yushchenko
We prove, that for each , and there are a collection of points and a - periodic function , such that (1)and for each trigonometric polynomial of degree (of order ), satisfying (2)the inequality holds, where is a constant, depending only on . Moreover, we prove, that for each and any such collection there is a - periodic function , such that is convex on , , and, for each sequence of trigonometric polynomials , satisfying (2), we have where is the fourth modulus of continuity.
中文翻译:
周期函数协凸近似的负结果
我们证明,对于每个 , 和 有一个收藏 点数 和一个 -周期性功能 ,使(1)对于每个三角多项式 度 (顺序 ),满足(2)不平等 持有,在哪里 是一个常数,仅取决于 。而且,我们证明,对于每个 以及任何此类收藏 有一个 -周期性功能 ,这样 凸在 , ,并且,对于每个序列 三角多项式 ,满足(2),我们有 在哪里 是第四连续模数。