<p>A result of Manning states that for a compact manifold <i>X</i> and a continuous map <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="209_2025_3827_Article_IEq1.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="86" /> </InlineMediaObject> <EquationSource Format="TEX">\(f: X \rightarrow X\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>f</mi> <mo>:</mo> <mi>X</mi> <mo stretchy="false">→</mo> <mi>X</mi> </mrow> </math></EquationSource> </InlineEquation> the topological entropy of <i>f</i> is bounded below by the logarithm of the spectral radius of the map induced by <i>f</i> in the first homology group <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="209_2025_3827_Article_IEq2.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="68" /> </InlineMediaObject> <EquationSource Format="TEX">\(H_1(X;\mathbb {C})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>H</mi> <mn>1</mn> </msub> <mrow> <mo stretchy="false">(</mo> <mi>X</mi> <mo>;</mo> <mi mathvariant="double-struck">C</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>. We generalize this result to arbitrary compact spaces <i>X</i> in terms of Čech cohomology <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="209_2025_3827_Article_IEq3.gif" Format="GIF" Height="21" Rendition="HTML" Resolution="72" Type="Linedraw" Width="69" /> </InlineMediaObject> <EquationSource Format="TEX">\(\check{H}^1(X;\mathbb {C})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mover accent="true"> <mi>H</mi> <mo stretchy="false">ˇ</mo> </mover> <mn>1</mn> </msup> <mrow> <mo stretchy="false">(</mo> <mi>X</mi> <mo>;</mo> <mi mathvariant="double-struck">C</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>. The essential tool is a notion of integration of Alexander-Spanier cocycles over Čech cycles. Most of the discussion is carried out “at scale <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="209_2025_3827_Article_IEq4.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="15" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathcal {U}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="script">U</mi> </math></EquationSource> </InlineEquation>”, for an open covering <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="209_2025_3827_Article_IEq4.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="15" /> </InlineMediaObject> <EquationSource Format="TEX">\(\mathcal {U}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="script">U</mi> </math></EquationSource> </InlineEquation>. This is used to keep track of the “homological length” of the iterates of a cycle, which in turn leads to a lower bound on the number of elements in the coverings that appear in the definition of the entropy.</p>

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A homological bound on entropy in arbitrary compact spaces

  • Luis Hernández-Corbato,
  • D. J. Nieves-Rivera,
  • Francisco R. Ruiz del Portal,
  • J. J. Sánchez-Gabites

摘要

A result of Manning states that for a compact manifold X and a continuous map \(f: X \rightarrow X\) f : X X the topological entropy of f is bounded below by the logarithm of the spectral radius of the map induced by f in the first homology group \(H_1(X;\mathbb {C})\) H 1 ( X ; C ) . We generalize this result to arbitrary compact spaces X in terms of Čech cohomology \(\check{H}^1(X;\mathbb {C})\) H ˇ 1 ( X ; C ) . The essential tool is a notion of integration of Alexander-Spanier cocycles over Čech cycles. Most of the discussion is carried out “at scale \(\mathcal {U}\) U ”, for an open covering \(\mathcal {U}\) U . This is used to keep track of the “homological length” of the iterates of a cycle, which in turn leads to a lower bound on the number of elements in the coverings that appear in the definition of the entropy.