<p>A point <i>x</i> is a point of approximative compactness for a&#xa0;set&#xa0;<i>M</i> if any minimizing sequence from&#xa0;<i>M</i> for&#xa0;<i>x</i> contains a&#xa0;subsequence converging to some point from&#xa0;<i>M</i>. We obtain several characterizations for points of approximative compactness for special subsets (a&#xa0;closed ball, the complement of an open ball) in classical sequence spaces <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(c_0(\Gamma )\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>c</mi> <mn>0</mn> </msub> <mrow> <mo stretchy="false">(</mo> <mi mathvariant="normal">Γ</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>, <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(c(\Gamma )\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>c</mi> <mo stretchy="false">(</mo> <mi mathvariant="normal">Γ</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>, <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(\ell ^p(\Gamma )\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mi>ℓ</mi> <mi>p</mi> </msup> <mrow> <mo stretchy="false">(</mo> <mi mathvariant="normal">Γ</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>, <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(1\le p\le \infty \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>1</mn> <mo>≤</mo> <mi>p</mi> <mo>≤</mo> <mi>∞</mi> </mrow> </math></EquationSource> </InlineEquation>.</p>

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APPROXIMATIVE COMPACTNESS IN CLASSICAL SEQUENCE SPACES

  • Hu Fang

摘要

A point x is a point of approximative compactness for a set M if any minimizing sequence from M for x contains a subsequence converging to some point from M. We obtain several characterizations for points of approximative compactness for special subsets (a closed ball, the complement of an open ball) in classical sequence spaces \(c_0(\Gamma )\) c 0 ( Γ ) , \(c(\Gamma )\) c ( Γ ) , \(\ell ^p(\Gamma )\) p ( Γ ) , \(1\le p\le \infty \) 1 p .