<p>We establish an improvement of the power-type weighted discrete variant of Hardy’s inequality in one dimension. To be specific, we establish the following inequality <Equation ID="Equ24"> <MediaObject> <ImageObject Color="BlackWhite" FileRef="12220_2025_2214_Article_Equ24.gif" Format="GIF" Height="48" Rendition="HTML" Resolution="72" Type="Linedraw" Width="571" /> </MediaObject> <EquationSource Format="TEX">\(\begin{aligned} \displaystyle \sum _{n=2}^{\infty }(n-1)^{\alpha }|A_{n}-A_{n-1}|^{2}&amp;\ge \displaystyle \sum _{n=2}^{\infty }\beta _{n}(\alpha )|A_{n}|^{2}&gt; \frac{(\alpha -1)^{2}}{4}\displaystyle \sum _{n=2}^{\infty }\frac{|A_{n}|^{2}}{n^{2-\alpha }}, ~~A_0=A_1=0, \end{aligned}\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mrow> <mtable> <mtr> <mtd columnalign="right"> <mstyle displaystyle="true" scriptlevel="0"> <mrow> <munderover> <mo>∑</mo> <mrow> <mi>n</mi> <mo>=</mo> <mn>2</mn> </mrow> <mi>∞</mi> </munderover> <msup> <mrow> <mo stretchy="false">(</mo> <mi>n</mi> <mo>-</mo> <mn>1</mn> <mo stretchy="false">)</mo> </mrow> <mi>α</mi> </msup> <msup> <mrow> <mo stretchy="false">|</mo> <msub> <mi>A</mi> <mi>n</mi> </msub> <mo>-</mo> <msub> <mi>A</mi> <mrow> <mi>n</mi> <mo>-</mo> <mn>1</mn> </mrow> </msub> <mo stretchy="false">|</mo> </mrow> <mn>2</mn> </msup> </mrow> </mstyle> </mtd> <mtd columnalign="left"> <mstyle displaystyle="true" scriptlevel="0"> <mrow> <mo>≥</mo> <munderover> <mo>∑</mo> <mrow> <mi>n</mi> <mo>=</mo> <mn>2</mn> </mrow> <mi>∞</mi> </munderover> <msub> <mi>β</mi> <mi>n</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>α</mi> <mo stretchy="false">)</mo> </mrow> <msup> <mrow> <mo stretchy="false">|</mo> <msub> <mi>A</mi> <mi>n</mi> </msub> <mo stretchy="false">|</mo> </mrow> <mn>2</mn> </msup> <mo>&gt;</mo> <mfrac> <msup> <mrow> <mo stretchy="false">(</mo> <mi>α</mi> <mo>-</mo> <mn>1</mn> <mo stretchy="false">)</mo> </mrow> <mn>2</mn> </msup> <mn>4</mn> </mfrac> <munderover> <mo>∑</mo> <mrow> <mi>n</mi> <mo>=</mo> <mn>2</mn> </mrow> <mi>∞</mi> </munderover> <mfrac> <mrow> <mrow> <mo stretchy="false">|</mo> </mrow> <msub> <mi>A</mi> <mi>n</mi> </msub> <msup> <mrow> <mo stretchy="false">|</mo> </mrow> <mn>2</mn> </msup> </mrow> <msup> <mi>n</mi> <mrow> <mn>2</mn> <mo>-</mo> <mi>α</mi> </mrow> </msup> </mfrac> <mo>,</mo> <mspace width="3.33333pt" /> <mspace width="3.33333pt" /> <msub> <mi>A</mi> <mn>0</mn> </msub> <mo>=</mo> <msub> <mi>A</mi> <mn>1</mn> </msub> <mo>=</mo> <mn>0</mn> <mo>,</mo> </mrow> </mstyle> </mtd> </mtr> </mtable> </mrow> </math></EquationSource> </Equation>where <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12220_2025_2214_Article_IEq1.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="67" /> </InlineMediaObject> <EquationSource Format="TEX">\(\alpha \in (1, 2]\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>α</mi> <mo>∈</mo> <mo stretchy="false">(</mo> <mn>1</mn> <mo>,</mo> <mn>2</mn> <mo stretchy="false">]</mo> </mrow> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12220_2025_2214_Article_IEq2.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="43" /> </InlineMediaObject> <EquationSource Format="TEX">\(\beta _{n}(\alpha )\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>β</mi> <mi>n</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>α</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> for <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12220_2025_2214_Article_IEq3.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="75" /> </InlineMediaObject> <EquationSource Format="TEX">\(2\le n\in {\mathbb {N}}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>2</mn> <mo>≤</mo> <mi>n</mi> <mo>∈</mo> <mi mathvariant="double-struck">N</mi> </mrow> </math></EquationSource> </InlineEquation> is an improved weight. In addition, it is shown that the improved weight sequence <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12220_2025_2214_Article_IEq2.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="43" /> </InlineMediaObject> <EquationSource Format="TEX">\(\beta _{n}(\alpha )\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>β</mi> <mi>n</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>α</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> is <i>critical</i>. Further, we study some fundamental structures of the sequence space <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12220_2025_2214_Article_IEq5.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="20" /> </InlineMediaObject> <EquationSource Format="TEX">\(\Sigma _p\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi mathvariant="normal">Σ</mi> <mi>p</mi> </msub> </math></EquationSource> </InlineEquation> for <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="12220_2025_2214_Article_IEq6.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="83" /> </InlineMediaObject> <EquationSource Format="TEX">\(1&lt;p&lt;\infty \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>1</mn> <mo>&lt;</mo> <mi>p</mi> <mo>&lt;</mo> <mi>∞</mi> </mrow> </math></EquationSource> </InlineEquation> originated from the improved inequality.</p>

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Improvement of the Discrete Weighted Variant Hardy’s Inequality and Criticality of the Improved Weight

  • Bikram Das,
  • Atanu Manna,
  • Tanmoy Paul

摘要

We establish an improvement of the power-type weighted discrete variant of Hardy’s inequality in one dimension. To be specific, we establish the following inequality \(\begin{aligned} \displaystyle \sum _{n=2}^{\infty }(n-1)^{\alpha }|A_{n}-A_{n-1}|^{2}&\ge \displaystyle \sum _{n=2}^{\infty }\beta _{n}(\alpha )|A_{n}|^{2}> \frac{(\alpha -1)^{2}}{4}\displaystyle \sum _{n=2}^{\infty }\frac{|A_{n}|^{2}}{n^{2-\alpha }}, ~~A_0=A_1=0, \end{aligned}\) n = 2 ( n - 1 ) α | A n - A n - 1 | 2 n = 2 β n ( α ) | A n | 2 > ( α - 1 ) 2 4 n = 2 | A n | 2 n 2 - α , A 0 = A 1 = 0 , where \(\alpha \in (1, 2]\) α ( 1 , 2 ] and \(\beta _{n}(\alpha )\) β n ( α ) for \(2\le n\in {\mathbb {N}}\) 2 n N is an improved weight. In addition, it is shown that the improved weight sequence \(\beta _{n}(\alpha )\) β n ( α ) is critical. Further, we study some fundamental structures of the sequence space \(\Sigma _p\) Σ p for \(1<p<\infty \) 1 < p < originated from the improved inequality.