{"title":"Stability and Inference of the Euler Characteristic Transform.","authors":"Lewis Marsh, David Beers","doi":"10.1007/s00454-025-00763-0","DOIUrl":"10.1007/s00454-025-00763-0","url":null,"abstract":"<p><p>The Euler characteristic transform (ECT) is a signature from topological data analysis (TDA) which summarises shapes embedded in Euclidean space. Compared with other TDA methods, the ECT is fast to compute and it is injective on a broad class of shapes. However, small perturbations of a shape can lead to large distortions in its ECT. In this paper, we propose a new metric on compact one-dimensional shapes and prove that the ECT is stable with respect to this metric. Crucially, our result uses curvature, rather than the size of a triangulation of an underlying shape, to control stability. We further construct a computationally tractable statistical estimator of the ECT based on the theory of Gaussian processes. We use our stability result to prove that our estimator is consistent on shapes perturbed by independent ambient noise; i.e., the estimator converges to the true ECT as the sample size increases.</p>","PeriodicalId":50574,"journal":{"name":"Discrete & Computational Geometry","volume":"75 3","pages":"795-838"},"PeriodicalIF":0.7,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13050334/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147628806","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Orr Dunkelman, Zeev Geyzel, Chaya Keller, Nathan Keller, Eyal Ronen, Adi Shamir, Ran J Tessler
{"title":"Error Resilient Space Partitioning.","authors":"Orr Dunkelman, Zeev Geyzel, Chaya Keller, Nathan Keller, Eyal Ronen, Adi Shamir, Ran J Tessler","doi":"10.1007/s00454-025-00804-8","DOIUrl":"10.1007/s00454-025-00804-8","url":null,"abstract":"<p><p>A major research area in discrete geometry is to consider the best way to partition the <i>d</i>-dimensional Euclidean space <math> <msup><mrow><mi>R</mi></mrow> <mi>d</mi></msup> </math> under various quality criteria. In this paper we introduce a new type of space partitioning that is motivated by the problem of rounding noisy measurements from the continuous space <math> <msup><mrow><mi>R</mi></mrow> <mi>d</mi></msup> </math> to a discrete subset of representative values. Specifically, we study partitions of <math> <msup><mrow><mi>R</mi></mrow> <mi>d</mi></msup> </math> into bounded-size tiles colored by one of <i>k</i> colors, such that tiles of the same color have a distance of at least <i>t</i> from each other. Such tilings allow for <i>error-resilient</i> rounding, as two points of the same color and distance less than <i>t</i> from each other are guaranteed to belong to the same tile, and thus, to be rounded to the same point. The main problem we study in this paper is characterizing the achievable tradeoffs between the number of colors <i>k</i> and the distance <i>t</i>, for various dimensions <i>d</i>. On the qualitative side, we show that in <math> <msup><mrow><mi>R</mi></mrow> <mi>d</mi></msup> </math> , using <math><mrow><mi>k</mi> <mo>=</mo> <mi>d</mi> <mo>+</mo> <mn>1</mn></mrow> </math> colors is both sufficient and necessary to achieve <math><mrow><mi>t</mi> <mo>></mo> <mn>0</mn></mrow> </math> . On the quantitative side, we achieve numerous upper and lower bounds on <i>t</i> as a function of <i>k</i>. In particular, for <math><mrow><mi>d</mi> <mo>=</mo> <mn>3</mn> <mo>,</mo> <mn>4</mn> <mo>,</mo> <mn>8</mn> <mo>,</mo> <mn>24</mn></mrow> </math> , we obtain sharp asymptotic bounds on <i>t</i>, as <math><mrow><mi>k</mi> <mo>→</mo> <mi>∞</mi></mrow> </math> . We obtain our results with a variety of techniques including isoperimetric inequalities, the Brunn-Minkowski theorem, sphere packing bounds, Bapat's connector-free lemma, and Čech cohomology.</p>","PeriodicalId":50574,"journal":{"name":"Discrete & Computational Geometry","volume":"75 3","pages":"839-870"},"PeriodicalIF":0.7,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13050337/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147628884","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"On Subsets of Lattice Cubes Avoiding Affine and Spherical Degeneracies.","authors":"Anubhab Ghosal, Ritesh Goenka, Peter Keevash","doi":"10.1007/s00454-026-00853-7","DOIUrl":"10.1007/s00454-026-00853-7","url":null,"abstract":"<p><p>For integers <math><mrow><mn>1</mn> <mo><</mo> <mi>k</mi> <mo><</mo> <mi>d</mi> <mo>-</mo> <mn>1</mn></mrow> </math> and <math><mrow><mi>r</mi> <mo>⩾</mo> <mi>k</mi> <mo>+</mo> <mn>2</mn></mrow> </math> , we establish new lower bounds on the maximum number of points in <math> <msup><mrow><mo>[</mo> <mi>n</mi> <mo>]</mo></mrow> <mi>d</mi></msup> </math> such that no <i>r</i> lie in a <i>k</i>-dimensional affine (or linear) subspace. These bounds improve on earlier results of Sudakov-Tomon and Lefmann. Further, we provide a randomised construction for the no-four-on-a-circle problem posed by Erdős and Purdy, improving Thiele's bound. We also consider the random construction in higher dimensions, and improve the bound of Suk and White for <math><mrow><mi>d</mi> <mo>⩾</mo> <mn>4</mn></mrow> </math> . In each case, we apply the deletion method, using results from number theory and incidence geometry to solve the associated counting problems.</p>","PeriodicalId":50574,"journal":{"name":"Discrete & Computational Geometry","volume":"76 3","pages":"1886-1911"},"PeriodicalIF":0.7,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13619741/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149082637","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Subword Complexes and Kalai's Conjecture on Reconstruction of Spheres.","authors":"Cesar Ceballos, Joseph Doolittle","doi":"10.1007/s00454-025-00733-6","DOIUrl":"https://doi.org/10.1007/s00454-025-00733-6","url":null,"abstract":"<p><p>A famous theorem in polytope theory states that the combinatorial type of a simplicial polytope is completely determined by its facet-ridge graph. This celebrated result was proven by Blind and Mani (Aequationes Math 34(2-3):287-297, 1987, 10.1007/BF01830678), via a non-constructive proof using topological tools from homology theory. An elegant constructive proof was given by Kalai shortly after. In their original paper, Blind and Mani asked whether their result can be extended to simplicial spheres, and a positive answer to their question was conjectured by Kalai (2009, https://gilkalai.wordpress.com/2009/01/16/telling-a-simple-polytope-from-its-graph/). In this paper, we show that Kalai's conjecture holds in the particular case of Knutson and Miller's spherical subword complexes. This family of simplicial spheres arises in the context of Coxeter groups, and is conjectured to be polytopal. In contrast, not all manifolds are reconstructible. We show two explicit examples, namely the torus and the projective plane.</p>","PeriodicalId":50574,"journal":{"name":"Discrete & Computational Geometry","volume":"74 1","pages":"23-48"},"PeriodicalIF":0.6,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12177012/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144477722","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Lech Duraj, Ross J Kang, Hoang La, Jonathan Narboni, Filip Pokrývka, Clément Rambaud, Amadeus Reinald
{"title":"<ArticleTitle xmlns:ns0=\"http://www.w3.org/1998/Math/MathML\">The <ns0:math><ns0:mi>χ</ns0:mi></ns0:math> -Binding Function of <i>d</i>-Directional Segment Graphs.","authors":"Lech Duraj, Ross J Kang, Hoang La, Jonathan Narboni, Filip Pokrývka, Clément Rambaud, Amadeus Reinald","doi":"10.1007/s00454-025-00737-2","DOIUrl":"https://doi.org/10.1007/s00454-025-00737-2","url":null,"abstract":"<p><p>Given a positive integer <i>d</i>, the class <i>d</i>-DIR is defined as all those intersection graphs formed from a finite collection of line segments in <math> <msup><mrow><mi>R</mi></mrow> <mn>2</mn></msup> </math> having at most <i>d</i> slopes. Since each slope induces an interval graph, it easily follows for every <i>G</i> in <i>d</i>-DIR with clique number at most <math><mi>ω</mi></math> that the chromatic number <math><mrow><mi>χ</mi> <mo>(</mo> <mi>G</mi> <mo>)</mo></mrow> </math> of <i>G</i> is at most <math><mrow><mi>d</mi> <mi>ω</mi></mrow> </math> . We show for every even value of <math><mi>ω</mi></math> how to construct a graph in <i>d</i>-DIR that meets this bound exactly. This partially confirms a conjecture of Bhattacharya, Dvořák and Noorizadeh. Furthermore, we show that the <math><mi>χ</mi></math> -binding function of <i>d</i>-DIR is <math><mrow><mi>ω</mi> <mo>↦</mo> <mi>d</mi> <mi>ω</mi></mrow> </math> for <math><mi>ω</mi></math> even and <math><mrow><mi>ω</mi> <mo>↦</mo> <mi>d</mi> <mo>(</mo> <mi>ω</mi> <mo>-</mo> <mn>1</mn> <mo>)</mo> <mo>+</mo> <mn>1</mn></mrow> </math> for <math><mi>ω</mi></math> odd. This extends an earlier result by Kostochka and Nešetřil, which treated the special case <math><mrow><mi>d</mi> <mo>=</mo> <mn>2</mn></mrow> </math> .</p>","PeriodicalId":50574,"journal":{"name":"Discrete & Computational Geometry","volume":"74 3","pages":"758-770"},"PeriodicalIF":0.6,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12484362/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145214309","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Compact Metric Spaces with Infinite Cop Number.","authors":"Agelos Georgakopoulos","doi":"10.1007/s00454-024-00696-0","DOIUrl":"https://doi.org/10.1007/s00454-024-00696-0","url":null,"abstract":"<p><p>Mohar recently adapted the classical game of Cops and Robber from graphs to metric spaces, thereby unifying previously studied pursuit-evasion games. He conjectured that finitely many cops can win on any compact geodesic metric space, and that their number can be upper-bounded in terms of the ranks of the homology groups when the space is a simplicial pseudo-manifold. We disprove these conjectures by constructing a metric on <math> <msup><mrow><mi>S</mi></mrow> <mn>3</mn></msup> </math> with infinite cop number. More problems are raised than settled.</p>","PeriodicalId":50574,"journal":{"name":"Discrete & Computational Geometry","volume":"74 3","pages":"793-804"},"PeriodicalIF":0.6,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12484412/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145214328","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Nóra Frankl, Panna Gehér, Arsenii Sagdeev, Géza Tóth
{"title":"Monochromatic Infinite Sets in Minkowski Planes.","authors":"Nóra Frankl, Panna Gehér, Arsenii Sagdeev, Géza Tóth","doi":"10.1007/s00454-024-00702-5","DOIUrl":"https://doi.org/10.1007/s00454-024-00702-5","url":null,"abstract":"<p><p>We prove that for any <math><msub><mi>ℓ</mi> <mi>p</mi></msub> </math> -norm in the plane with <math><mrow><mn>1</mn> <mo><</mo> <mi>p</mi> <mo><</mo> <mi>∞</mi></mrow> </math> and for every infinite <math><mrow><mi>M</mi> <mo>⊂</mo> <msup><mrow><mi>R</mi></mrow> <mn>2</mn></msup> </mrow> </math> , there exists a two-colouring of the plane such that no isometric copy of <math><mi>M</mi></math> is monochromatic. On the contrary, we show that for every polygonal norm (that is, the unit ball is a polygon) in the plane, there exists an infinite <math><mrow><mi>M</mi> <mo>⊂</mo> <msup><mrow><mi>R</mi></mrow> <mn>2</mn></msup> </mrow> </math> such that for every two-colouring of the plane there exists a monochromatic isometric copy of <math><mi>M</mi></math> .</p>","PeriodicalId":50574,"journal":{"name":"Discrete & Computational Geometry","volume":"74 2","pages":"569-583"},"PeriodicalIF":0.6,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12449424/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145114837","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Rigidity of Symmetric Frameworks on the Cylinder.","authors":"Anthony Nixon, Bernd Schulze, Joseph Wall","doi":"10.1007/s00454-025-00723-8","DOIUrl":"https://doi.org/10.1007/s00454-025-00723-8","url":null,"abstract":"<p><p>A bar-joint framework (<i>G</i>, <i>p</i>) is the combination of a finite simple graph <math><mrow><mi>G</mi> <mo>=</mo> <mo>(</mo> <mi>V</mi> <mo>,</mo> <mi>E</mi> <mo>)</mo></mrow> </math> and a placement <math><mrow><mi>p</mi> <mo>:</mo> <mi>V</mi> <mo>→</mo> <msup><mrow><mi>R</mi></mrow> <mi>d</mi></msup> </mrow> </math> . The framework is rigid if the only edge-length preserving continuous motions of the vertices arise from isometries of the space. This article combines two recent extensions of the generic theory of rigid and flexible graphs by considering symmetric frameworks in <math> <msup><mrow><mi>R</mi></mrow> <mn>3</mn></msup> </math> restricted to move on a surface. In particular necessary combinatorial conditions are given for a symmetric framework on the cylinder to be isostatic (i.e. minimally infinitesimally rigid) under any finite point group symmetry. In every case when the symmetry group is cyclic, which we prove restricts the group to being inversion, half-turn or reflection symmetry, these conditions are then shown to be sufficient under suitable genericity assumptions, giving precise combinatorial descriptions of symmetric isostatic graphs in these contexts.</p>","PeriodicalId":50574,"journal":{"name":"Discrete & Computational Geometry","volume":"73 3","pages":"629-673"},"PeriodicalIF":0.6,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11914369/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143665211","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Decomposition of Zero-Dimensional Persistence Modules via Rooted Subsets.","authors":"Ángel Javier Alonso, Michael Kerber","doi":"10.1007/s00454-024-00700-7","DOIUrl":"https://doi.org/10.1007/s00454-024-00700-7","url":null,"abstract":"<p><p>We study the decomposition of zero-dimensional persistence modules, viewed as functors valued in the category of vector spaces factorizing through sets. Instead of working directly at the level of vector spaces, we take a step back and first study the decomposition problem at the level of sets. This approach allows us to define the combinatorial notion of <i>rooted subsets</i>. In the case of a filtered metric space <i>M</i>, rooted subsets relate the clustering behavior of the points of <i>M</i> with the decomposition of the associated persistence module. In particular, we can identify intervals in such a decomposition quickly. In addition, rooted subsets can be understood as a generalization of the elder rule, and are also related to the notion of constant conqueror of Cai, Kim, Mémoli and Wang. As an application, we give a lower bound on the number of intervals that we can expect in the decomposition of zero-dimensional persistence modules of a density-Rips filtration in Euclidean space: in the limit, and under very general circumstances, we can expect that at least 25% of the indecomposable summands are interval modules.</p>","PeriodicalId":50574,"journal":{"name":"Discrete & Computational Geometry","volume":"74 4","pages":"818-838"},"PeriodicalIF":0.6,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12662898/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145649970","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Greg Aloupis, John Iacono, Stefan Langerman, Özgür Özkan, Stefanie Wuhrer
{"title":"The Complexity of Order Type Isomorphism","authors":"Greg Aloupis, John Iacono, Stefan Langerman, Özgür Özkan, Stefanie Wuhrer","doi":"10.1007/s00454-024-00687-1","DOIUrl":"https://doi.org/10.1007/s00454-024-00687-1","url":null,"abstract":"<p>The order type of a point set in <span>(mathbb {R}^d)</span> maps each <span>((d{+}1))</span>-tuple of points to its orientation (e.g., clockwise or counterclockwise in <span>(mathbb {R}^2)</span>). Two point sets <i>X</i> and <i>Y</i> have the same order type if there exists a bijection <i>f</i> from <i>X</i> to <i>Y</i> for which every <span>((d{+}1))</span>-tuple <span>((a_1,a_2,ldots ,a_{d+1}))</span> of <i>X</i> and the corresponding tuple <span>((f(a_1),f(a_2),ldots ,f(a_{d+1})))</span> in <i>Y</i> have the same orientation. In this paper we investigate the complexity of determining whether two point sets have the same order type. We provide an <span>(O(n^d))</span> algorithm for this task, thereby improving upon the <span>(O(n^{lfloor {3d/2}rfloor }))</span> algorithm of Goodman and Pollack (SIAM J. Comput. 12(3):484–507, 1983). The algorithm uses only order type queries and also works for abstract order types (or acyclic oriented matroids). Our algorithm is optimal, both in the abstract setting and for realizable points sets if the algorithm only uses order type queries.\u0000</p>","PeriodicalId":50574,"journal":{"name":"Discrete & Computational Geometry","volume":"141 1","pages":""},"PeriodicalIF":0.8,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142253141","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}