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The Maximum Modulus Set of a Polynomial
Computational Methods and Function Theory ( IF 0.6 ) Pub Date : 2021-03-01 , DOI: 10.1007/s40315-021-00368-7
Leticia Pardo-Simón , David J. Sixsmith

We study the maximum modulus set, \({{\mathcal {M}}}(p)\), of a polynomial p. We are interested in constructing p so that \({{\mathcal {M}}}(p)\) has certain exceptional features. Jassim and London gave a cubic polynomial p such that \({{\mathcal {M}}}(p)\) has one discontinuity, and Tyler found a quintic polynomial \({\tilde{p}}\) such that \({{\mathcal {M}}}({\tilde{p}})\) has one singleton component. These are the only results of this type, and we strengthen them considerably. In particular, given a finite sequence \(a_1, a_2, \ldots , a_n\) of distinct positive real numbers, we construct polynomials p and \({\tilde{p}}\) such that \({{\mathcal {M}}}(p)\) has discontinuities of modulus \(a_1, a_2, \ldots , a_n\), and \({{\mathcal {M}}}({\tilde{p}})\) has singleton components at the points \(a_1, a_2, \ldots , a_n\). Finally we show that these results are strong, in the sense that it is not possible for a polynomial to have infinitely many discontinuities in its maximum modulus set.



中文翻译:

多项式的最大模集

我们研究多项式p的最大模数集\({{\ mathcal {M}}}(p)\)。我们对构造p感兴趣,因此\({{\ mathcal {M}}}(p)\)具有某些特殊功能。Jassim和London给出了三次多项式p,使得\({{\ mathcal {M}}}(p)\)具有一个不连续点,而Tyler找到了一个五次多项式\({\ tilde {p}} \)使得\ ({{\ mathcal {M}}}({\ tilde {p}})\)具有一个单例分量。这些是这种类型的唯一结果,我们将对其进行大力增强。特别是,给定一个不同的正实数的有限序列\(a_1,a_2,\ ldots,a_n \),我们可以构造多项式p\({\ tilde {p}} \),这样\({{\ mathcal {M}}}(p)\)具有模数\ {a_1,a_2,\ ldots,a_n \)\ ({{\ mathcal {M}}}({\ tilde {p}})\)在点\(a_1,a_2,\ ldots,a_n \)处具有单例分量。最后,从多项式在其最大模数集中不可能具有无限多个不连续的意义上说,这些结果很强。

更新日期:2021-03-01
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