<p>For a positive integer <i>n</i> and a finite simplicial complex <i>K</i>, we describe an algorithmic procedure constructing a maximal discrete gradient field <i>W</i>(<i>K</i>,&#xa0;<i>n</i>) on Abrams’ discretized configuration space <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="29_2025_1043_Article_IEq1.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="92" /> </InlineMediaObject> <EquationSource Format="TEX">\(\operatorname {DConf}(K,n)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo>DConf</mo> <mo stretchy="false">(</mo> <mi>K</mi> <mo>,</mo> <mi>n</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>. Computer experimentation suggests that the field is optimal for <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="29_2025_1043_Article_IEq2.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="42" /> </InlineMediaObject> <EquationSource Format="TEX">\(n=2\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>n</mi> <mo>=</mo> <mn>2</mn> </mrow> </math></EquationSource> </InlineEquation> and complexes <i>K</i> such as triangulations of surfaces. We study the field <i>W</i>(<i>K</i>,&#xa0;<i>n</i>) for <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="29_2025_1043_Article_IEq2.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="42" /> </InlineMediaObject> <EquationSource Format="TEX">\(n=2\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>n</mi> <mo>=</mo> <mn>2</mn> </mrow> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="29_2025_1043_Article_IEq4.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="74" /> </InlineMediaObject> <EquationSource Format="TEX">\(K=\Delta ^{m,d}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>K</mi> <mo>=</mo> <msup> <mi mathvariant="normal">Δ</mi> <mrow> <mi>m</mi> <mo>,</mo> <mi>d</mi> </mrow> </msup> </mrow> </math></EquationSource> </InlineEquation>, the <i>d</i>-dimensional skeleton of the <i>m</i>-dimensional simplex. In particular, we prove that <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="29_2025_1043_Article_IEq5.gif" Format="GIF" Height="21" Rendition="HTML" Resolution="72" Type="Linedraw" Width="109" /> </InlineMediaObject> <EquationSource Format="TEX">\(\operatorname {DConf}(\Delta ^{m,d},2)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo>DConf</mo> <mo stretchy="false">(</mo> <msup> <mi mathvariant="normal">Δ</mi> <mrow> <mi>m</mi> <mo>,</mo> <mi>d</mi> </mrow> </msup> <mo>,</mo> <mn>2</mn> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> is <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="29_2025_1043_Article_IEq6.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="146" /> </InlineMediaObject> <EquationSource Format="TEX">\((\min \{d,m-1\}-1)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mo movablelimits="true">min</mo> <mo stretchy="false">{</mo> <mi>d</mi> <mo>,</mo> <mi>m</mi> <mo>-</mo> <mn>1</mn> <mo stretchy="false">}</mo> <mo>-</mo> <mn>1</mn> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>-connected, has torsion-free homology and admits a minimal cell structure. We compute the Betti numbers of <InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="29_2025_1043_Article_IEq5.gif" Format="GIF" Height="21" Rendition="HTML" Resolution="72" Type="Linedraw" Width="109" /> </InlineMediaObject> <EquationSource Format="TEX">\(\operatorname {DConf}(\Delta ^{m,d},2)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo>DConf</mo> <mo stretchy="false">(</mo> <msup> <mi mathvariant="normal">Δ</mi> <mrow> <mi>m</mi> <mo>,</mo> <mi>d</mi> </mrow> </msup> <mo>,</mo> <mn>2</mn> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> and, for certain values of <i>d</i>, we prove that <InlineEquation ID="IEq8"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="29_2025_1043_Article_IEq5.gif" Format="GIF" Height="21" Rendition="HTML" Resolution="72" Type="Linedraw" Width="109" /> </InlineMediaObject> <EquationSource Format="TEX">\(\operatorname {DConf}(\Delta ^{m,d},2)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo>DConf</mo> <mo stretchy="false">(</mo> <msup> <mi mathvariant="normal">Δ</mi> <mrow> <mi>m</mi> <mo>,</mo> <mi>d</mi> </mrow> </msup> <mo>,</mo> <mn>2</mn> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> breaks, up to homotopy, as a wedge of (not necessarily equidimensional) spheres.</p>

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An algorithmic discrete gradient field for non-colliding cell-like objects and the topology of pairs of points on skeleta of simplexes

  • Emilio J. González,
  • Jesús González

摘要

For a positive integer n and a finite simplicial complex K, we describe an algorithmic procedure constructing a maximal discrete gradient field W(Kn) on Abrams’ discretized configuration space \(\operatorname {DConf}(K,n)\) DConf ( K , n ) . Computer experimentation suggests that the field is optimal for \(n=2\) n = 2 and complexes K such as triangulations of surfaces. We study the field W(Kn) for \(n=2\) n = 2 and \(K=\Delta ^{m,d}\) K = Δ m , d , the d-dimensional skeleton of the m-dimensional simplex. In particular, we prove that \(\operatorname {DConf}(\Delta ^{m,d},2)\) DConf ( Δ m , d , 2 ) is \((\min \{d,m-1\}-1)\) ( min { d , m - 1 } - 1 ) -connected, has torsion-free homology and admits a minimal cell structure. We compute the Betti numbers of \(\operatorname {DConf}(\Delta ^{m,d},2)\) DConf ( Δ m , d , 2 ) and, for certain values of d, we prove that \(\operatorname {DConf}(\Delta ^{m,d},2)\) DConf ( Δ m , d , 2 ) breaks, up to homotopy, as a wedge of (not necessarily equidimensional) spheres.