Pub Date : 2024-01-31DOI: 10.1007/s10474-024-01395-1
A. Dalal, N. K. Govil
Finding the sharp estimate of (max_{|z|=1} |p'(z)|) in terms of (max_{|z|=1} |p(z)|) for the class of polynomials p(z) satisfying (p(z) equiv z^n p(1/z)) has been a well-known open problem for a long time and many papers in this direction have appeared. The earliest result is due to Govil, Jain and Labelle [9] who proved that for polynomials p(z) satisfying (p(z) equiv z^n p(1/z)) and having all the zeros either in left half or right half-plane, the inequality (max_{|z|=1} |p'(z)| le frac{n}{sqrt{2}} max_{|z|=1} |p(z)|) holds. A question was posed whether this inequality is sharp. In this paper, we answer this question in the negative by obtaining a bound sharper than (frac{n}{sqrt{2}}). We also conjecture that for such polynomials
$$max_{|z|=1} |p'(z)| le Big(frac{n}{sqrt{2}} - frac{sqrt{2}-1}{4}(n-2)Big) max_{|z|=1} |p(z)|$$
and provide evidence in support of this conjecture.
{"title":"Inequalities for polynomials satisfying $$p(z)equiv z^np(1/z)$$","authors":"A. Dalal, N. K. Govil","doi":"10.1007/s10474-024-01395-1","DOIUrl":"https://doi.org/10.1007/s10474-024-01395-1","url":null,"abstract":"<p>Finding the sharp estimate of <span>(max_{|z|=1} |p'(z)|)</span> in terms of <span>(max_{|z|=1} |p(z)|)</span> for the class of polynomials p(z) satisfying <span>(p(z) equiv z^n p(1/z))</span> has been a well-known open problem for a long time and many papers in this direction have appeared. The earliest result is due to Govil, Jain and Labelle [9] who proved that for polynomials p(z) satisfying <span>(p(z) equiv z^n p(1/z))</span> and having all the zeros either in left half or right half-plane, the inequality <span>(max_{|z|=1} |p'(z)| le frac{n}{sqrt{2}} max_{|z|=1} |p(z)|)</span> holds. A question was posed whether this inequality is sharp. In this paper, we answer this question in the negative by obtaining a bound sharper than <span>(frac{n}{sqrt{2}})</span>. We also conjecture that for such polynomials </p><span>$$max_{|z|=1} |p'(z)| le Big(frac{n}{sqrt{2}} - frac{sqrt{2}-1}{4}(n-2)Big) max_{|z|=1} |p(z)|$$</span><p> and provide evidence in support of this conjecture.</p>","PeriodicalId":50894,"journal":{"name":"Acta Mathematica Hungarica","volume":null,"pages":null},"PeriodicalIF":0.9,"publicationDate":"2024-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139646978","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-12-13DOI: 10.1007/s10474-023-01384-w
D. Baramidze, G. Tephnadze
We introduce some new weighted maximal operators of the Fejér means of the Walsh–Fourier series. We prove that for some "optimal" weights these new operators are bounded from the martingale Hardy space (H_{p}(G)) to the space (text{weak-}L_{p}(G)) , for (0<p<1/2). Moreover, we also prove sharpness of this result. As a consequence we obtain some new and well-known results.
{"title":"Some New weak-( $$H_{p}-L_p$$ ) Type Inequalities For Weighted Maximal Operators Of Fejér Means Of Walsh–Fourier Series","authors":"D. Baramidze, G. Tephnadze","doi":"10.1007/s10474-023-01384-w","DOIUrl":"https://doi.org/10.1007/s10474-023-01384-w","url":null,"abstract":"<p>We introduce some new weighted maximal operators of the Fejér means of the Walsh–Fourier series. We prove that for some \"optimal\" weights these new operators are bounded from the martingale Hardy space <span>(H_{p}(G))</span> to the space <span>(text{weak-}L_{p}(G))</span> , for <span>(0<p<1/2)</span>. Moreover, we also prove sharpness of this result. As a consequence we obtain some new and well-known results.\u0000</p>","PeriodicalId":50894,"journal":{"name":"Acta Mathematica Hungarica","volume":null,"pages":null},"PeriodicalIF":0.9,"publicationDate":"2023-12-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138628503","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}