<p>In this paper, we introduce a new family of combinatorial cubical complexes <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41468_2025_204_Article_IEq1.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="64" /> </InlineMediaObject> <EquationSource Format="TEX">\(\{X_n\}_{n\ge 1}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mrow> <mo stretchy="false">{</mo> <msub> <mi>X</mi> <mi>n</mi> </msub> <mo stretchy="false">}</mo> </mrow> <mrow> <mi>n</mi> <mo>≥</mo> <mn>1</mn> </mrow> </msub> </math></EquationSource> </InlineEquation>. Each such complex <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41468_2025_204_Article_IEq2.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="24" /> </InlineMediaObject> <EquationSource Format="TEX">\(X_n\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>X</mi> <mi>n</mi> </msub> </math></EquationSource> </InlineEquation> models the process of updating spanning tree networks on <i>n</i> vertices over time. The vertices of these complexes model the networks themselves, whereas the higher-dimensional cubes model the network realignments. Such realignments may become necessary in order to maintain the connectivity of the networks by local changes, in case the connections to the leaves become weak. Our goal is to study the topology of <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41468_2025_204_Article_IEq3.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="24" /> </InlineMediaObject> <EquationSource Format="TEX">\(X_n\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>X</mi> <mi>n</mi> </msub> </math></EquationSource> </InlineEquation>. Our main result states that for any <i>n</i>, there exists a strong deformation retraction from the complex <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41468_2025_204_Article_IEq4.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="24" /> </InlineMediaObject> <EquationSource Format="TEX">\(X_n\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>X</mi> <mi>n</mi> </msub> </math></EquationSource> </InlineEquation> to the complete graph <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41468_2025_204_Article_IEq5.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="24" /> </InlineMediaObject> <EquationSource Format="TEX">\(K_n\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>K</mi> <mi>n</mi> </msub> </math></EquationSource> </InlineEquation>, the latter viewed as a topological space. In particular, the homology vanishes in dimensions 2, and above, and, in fact, these complexes are homotopy equivalent to wedges of circles.</p>

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Network realignment complexes

  • Dmitry N. Kozlov

摘要

In this paper, we introduce a new family of combinatorial cubical complexes \(\{X_n\}_{n\ge 1}\) { X n } n 1 . Each such complex \(X_n\) X n models the process of updating spanning tree networks on n vertices over time. The vertices of these complexes model the networks themselves, whereas the higher-dimensional cubes model the network realignments. Such realignments may become necessary in order to maintain the connectivity of the networks by local changes, in case the connections to the leaves become weak. Our goal is to study the topology of \(X_n\) X n . Our main result states that for any n, there exists a strong deformation retraction from the complex \(X_n\) X n to the complete graph \(K_n\) K n , the latter viewed as a topological space. In particular, the homology vanishes in dimensions 2, and above, and, in fact, these complexes are homotopy equivalent to wedges of circles.