<p>In 1957, Hadwiger conjectured that every <i>n</i>-dimensional convex body can be covered by <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(2^n\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mn>2</mn> <mi>n</mi> </msup> </math></EquationSource> </InlineEquation> translations of its interior. The covering functional <i>f</i>(<i>K</i>), defined as the smallest positive number <i>r</i> such that <i>K</i> can be covered by <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(2^n\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mn>2</mn> <mi>n</mi> </msup> </math></EquationSource> </InlineEquation> translations of <i>rK</i>, provides a natural framework for studying this conjecture. In particular, Hadwiger’s conjecture is equivalent to the statement that <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(\max _{K}f(K)\le c&lt;1\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mo movablelimits="true">max</mo> <mi>K</mi> </msub> <mi>f</mi> <mrow> <mo stretchy="false">(</mo> <mi>K</mi> <mo stretchy="false">)</mo> </mrow> <mo>≤</mo> <mi>c</mi> <mo>&lt;</mo> <mn>1</mn> </mrow> </math></EquationSource> </InlineEquation> for some positive constant <i>c</i>. In this work, we investigate the covering functionals for two fundamental classes of convex bodies: the <i>n</i>-dimensional simplex <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(S_n\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>S</mi> <mi>n</mi> </msub> </math></EquationSource> </InlineEquation> and the cross-polytope <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(C_n^\star \)</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mi>C</mi> <mi>n</mi> <mo>⋆</mo> </msubsup> </math></EquationSource> </InlineEquation>. We establish the upper bounds: <Equation ID="Equ23"> <EquationSource Format="TEX">\(\begin{aligned} \underset{n\rightarrow \infty }{\text {lim sup}}f(S_n)\le 0.773\cdots ~~~~\text {and}~~~~ \underset{n\rightarrow \infty }{\text {lim sup}}f(C_n^\star )\le 0.824\cdots . \end{aligned}\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mrow> <mtable> <mtr> <mtd columnalign="right"> <mrow> <munder> <mrow> <mtext>lim sup</mtext> </mrow> <mrow> <mi>n</mi> <mo stretchy="false">→</mo> <mi>∞</mi> </mrow> </munder> <mi>f</mi> <mrow> <mo stretchy="false">(</mo> <msub> <mi>S</mi> <mi>n</mi> </msub> <mo stretchy="false">)</mo> </mrow> <mo>≤</mo> <mn>0.773</mn> <mo>⋯</mo> <mspace width="3.33333pt" /> <mspace width="3.33333pt" /> <mspace width="3.33333pt" /> <mspace width="3.33333pt" /> <mtext>and</mtext> <mspace width="3.33333pt" /> <mspace width="3.33333pt" /> <mspace width="3.33333pt" /> <mspace width="3.33333pt" /> <munder> <mrow> <mtext>lim sup</mtext> </mrow> <mrow> <mi>n</mi> <mo stretchy="false">→</mo> <mi>∞</mi> </mrow> </munder> <mi>f</mi> <mrow> <mo stretchy="false">(</mo> <msubsup> <mi>C</mi> <mi>n</mi> <mo>⋆</mo> </msubsup> <mo stretchy="false">)</mo> </mrow> <mo>≤</mo> <mn>0.824</mn> <mo>⋯</mo> <mo>.</mo> </mrow> </mtd> </mtr> </mtable> </mrow> </math></EquationSource> </Equation>Moreover, the method developed in this study can be further extended to investigate the covering functionals of quarter-<InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(\ell _p\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>ℓ</mi> <mi>p</mi> </msub> </math></EquationSource> </InlineEquation> balls and <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(\ell _p\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>ℓ</mi> <mi>p</mi> </msub> </math></EquationSource> </InlineEquation> balls. These results establish the first non-trivial asymptotic upper bounds for the covering functionals of these fundamental convex bodies. Furthermore, they imply estimates for the dyadic entropy numbers of identity operators on finite-dimensional <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\(\ell _p^n\)</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mi>ℓ</mi> <mi>p</mi> <mi>n</mi> </msubsup> </math></EquationSource> </InlineEquation> spaces.</p>

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On the Covering Functionals of Simplices and Cross-Polytopes

  • Yanlu Lian,
  • Yu Xia,
  • Fei Xue,
  • Yuqin Zhang

摘要

In 1957, Hadwiger conjectured that every n-dimensional convex body can be covered by \(2^n\) 2 n translations of its interior. The covering functional f(K), defined as the smallest positive number r such that K can be covered by \(2^n\) 2 n translations of rK, provides a natural framework for studying this conjecture. In particular, Hadwiger’s conjecture is equivalent to the statement that \(\max _{K}f(K)\le c<1\) max K f ( K ) c < 1 for some positive constant c. In this work, we investigate the covering functionals for two fundamental classes of convex bodies: the n-dimensional simplex \(S_n\) S n and the cross-polytope \(C_n^\star \) C n . We establish the upper bounds: \(\begin{aligned} \underset{n\rightarrow \infty }{\text {lim sup}}f(S_n)\le 0.773\cdots ~~~~\text {and}~~~~ \underset{n\rightarrow \infty }{\text {lim sup}}f(C_n^\star )\le 0.824\cdots . \end{aligned}\) lim sup n f ( S n ) 0.773 and lim sup n f ( C n ) 0.824 . Moreover, the method developed in this study can be further extended to investigate the covering functionals of quarter- \(\ell _p\) p balls and \(\ell _p\) p balls. These results establish the first non-trivial asymptotic upper bounds for the covering functionals of these fundamental convex bodies. Furthermore, they imply estimates for the dyadic entropy numbers of identity operators on finite-dimensional \(\ell _p^n\) p n spaces.