GAMBLE

GAMBLE - 2023

2023Activity reportProject-TeamGAMBLE

RNSR: 201722240E

Research center Inria Centre at Université de Lorraine
In partnership with:Université de Lorraine
Team name: Geometric Algorithms & Models Beyond the Linear & Euclidean realm
In collaboration with:Laboratoire lorrain de recherche en informatique et ses applications (LORIA)
Domain:Algorithmics, Programming, Software and Architecture
Theme:Algorithmics, Computer Algebra and Cryptology

Keywords

Computer Science and Digital Science

A5.5.1. Geometrical modeling
A5.10.1. Design
A7.1. Algorithms
A8.1. Discrete mathematics, combinatorics
A8.3. Geometry, Topology
A8.4. Computer Algebra

1 Team members, visitors, external collaborators

Research Scientists

Olivier Devillers [Team leader, INRIA, Senior Researcher, HDR]
Sylvain Lazard [INRIA, Senior Researcher, HDR]
Guillaume Moroz [INRIA, Researcher]
Marc Pouget [INRIA, Researcher, HDR]
Monique Teillaud [INRIA, Senior Researcher, HDR]

Faculty Members

Vincent Despre [UL, Associate Professor]
Laurent Dupont [UL, Associate Professor]
Xavier Goaoc [UL, Professor, HDR]
Alba Marina Malaga Sabogal [UL, Associate Professor]

Post-Doctoral Fellow

Florent Koechlin [INRIA, Post-Doctoral Fellow, until Aug 2023]

PhD Students

Loïc Dubois [Université Gustave Eiffel]
Nuwan Herath Mudiyanselage [UL, ATER, until Aug 2023]
Camille Lanuel [UL]
Leo Valque [UL, ATER, from Sep 2023]
Leo Valque [UL, until Aug 2023]
Sarah Wajsbrot [UL, from Oct 2023]

Technical Staff

Rémi Imbach [INRIA, Engineer, until Oct 2023]

Interns and Apprentices

Pierre Anxionnat [UL, Intern, until Aug 2023]
Marguerite Bin [ENS Lyon, Intern, from Oct 2023]
Taekang Eom [INRIA, Intern, until Feb 2023]
Sarah Wajsbrot [INRIA, Intern, from Apr 2023 until Sep 2023]

Administrative Assistant

Cecilia Olivier [INRIA, from Jul 2023]

External Collaborator

Valentin Feray [CNRS, HDR]

2 Overall objectives

Starting in the eighties, the emerging computational geometry community has put a lot of effort into designing and analyzing algorithms for geometric problems. The most commonly used framework was to study the worst-case theoretical complexity of geometric problems involving linear objects (points, lines, polyhedra...) in Euclidean spaces. This so-called classical computational geometry has some known limitations:

Objects: dealing with objects only defined by linear equations.
Ambient space: considering only Euclidean spaces.
Complexity: worst-case complexities often do not capture realistic behaviour.
Dimension: complexities are often exponential in the dimension.
Robustness: ignoring degeneracies and rounding errors.

Even if these limitations have already got some attention from the community 43, a quick look at the proceedings of the flagship conference SoCG1 shows that these topics still need a big effort.

It should be stressed that, in this document, the notion of certified algorithms is to be understood with respect to robustness issues. In other words, certification does not refer to programs that are proven correct with the help of mechanical proof assistants such as Coq, but to algorithms that are proven correct on paper even in the presence of degeneracies and computer-induced numerical rounding errors.

We address several of the above limitations:

$•$ Non-linear computational geometry. Curved objects are ubiquitous in the world we live in. However, despite this ubiquity and decades of research in several communities, curved objects are far from being robustly and efficiently manipulated by geometric algorithms. Our work on, for instance, quadric intersections and certified drawing of plane curves has proven that dramatic improvements can be accomplished when the right mathematics and computer science concepts are put into motion. In this direction, many problems are fundamental and solutions have potential industrial impact in Computer Aided Design and Robotics for instance. Intersecting NURBS (Non-uniform rational basis splines) and meshing singular surfaces in a certified manner are important examples of such problems.

$•$ Non-Euclidean computational geometry. Triangulations are central geometric data structures in many areas of science and engineering. Traditionally, their study has been limited to the Euclidean setting. Needs for triangulations in non-Euclidean settings have emerged in many areas dealing with objects whose sizes range from the nuclear to the astrophysical scale, and both in academia and in industry. It has become timely to extend the traditional focus on $ℝ^{d}$ of computational geometry and encompass non-Euclidean spaces.

$•$ Probability in computational geometry. The design of efficient algorithms is driven by the analysis of their complexity. Traditionally, worst-case input and sometimes uniform distributions are considered and many results in these settings have had a great influence on the domain. Nowadays, it is necessary to be more subtle and to prove new results in between these two extreme settings. For instance, smoothed analysis, which was introduced for the simplex algorithm and which we applied successfully to convex hulls, proves that such promising alternatives exist.

$•$ Discrete geometric structures. Many geometric algorithms work, explicitly or implicitly, over discrete structures such as graphs, hypergraphs, lattices that are induced by the geometric input data. For example, convex hulls or straight-line graph drawing are essentially based on orientation predicates, and therefore operate on the so-called order type of the input point set. Order types are a subclass of oriented matroids that remains poorly understood: for instance, we do not even know how to sample this space with reasonable bias. One of our goals is to contribute to the development of these foundations by better understanding these discrete geometric structures.

3 Research program

3.1 Non-linear computational geometry

Figure 1.a — Figure1: Two views of the Whitney umbrella (on the left, the “stick” of the umbrella, i.e., the negative $z$ -axis, is missing). Right picture from [Wikipedia], left picture from [Lachaud et al.].

Figure 1.b — Figure1: Two views of the Whitney umbrella (on the left, the “stick” of the umbrella, i.e., the negative $z$ -axis, is missing). Right picture from [Wikipedia], left picture from [Lachaud et al.].

As mentioned above, curved objects are ubiquitous in real world problems and in computer science and, despite this fact, there are very few problems on curved objects that admit robust and efficient algorithmic solutions without first discretizing the curved objects into meshes. Meshing curved objects induces a loss of accuracy which is sometimes not an issue but which can also be most problematic depending on the application. In addition, discretization induces a combinatorial explosion which could cause a loss in efficiency compared to a direct solution on the curved objects (as our work on quadrics has demonstrated with flying colors 51, 52, 50, 54, 58). But it is also crucial to know that even the process of computing meshes that approximate curved objects is far from being resolved. As a matter of fact there is no algorithm capable of computing in practice meshes with certified topology of even rather simple singular (that is auto-intersecting) 3D surfaces, due to the high constants in the theoretical complexity and the difficulty of handling degenerate cases. Part of the difficulty comes from the unintuitive fact that the structure of an algebraic object can be quite complicated, as depicted in the Whitney umbrella (see Figure 1), the surface with equation $x^{2} = y^{2} z$ whose origin (the “special” point of the surface) is a vertex of the arrangement induced by the surface while the singular locus is simply the whole $z$ -axis. Even in 2D, meshing an algebraic curve with the correct topology, that is in other words producing a correct drawing of the curve (without knowing where the domain of interest is), is a very difficult problem on which we have recently made important contributions 36, 379.

Thus producing practical, robust, and efficient algorithmic solutions to geometric problems on curved objects is a challenge on all and even the most basic problems. The basicness and fundamentality of the two problems we mentioned above on the intersection of 3D quadrics and on the drawing in a topologically certified way of plane algebraic curves show rather well that the domain is still in its infancy. And it should be stressed that these two sets of results were not anecdotal but flagship results produced during the lifetime of the Vegas team (the team preceding Gamble).

There are many problems in this theme that are expected to have high long-term impacts. Intersecting NURBS (Non-uniform rational basis splines) in a certified way is an important problem in computer-aided design and manufacturing. As hinted above, meshing objects in a certified way is important when topology matters. The 2D case, that is essentially drawing plane curves with the correct topology, is a fundamental problem with far-reaching applications in research or R&D. Notice that on such elementary problems it is often difficult to predict the reach of the applications; as an example, we were astonished by the scope of the applications of our software on 3D quadric intersection2 which was used by researchers in, for instance, photochemistry, computer vision, statistics and mathematics.

3.2 Non-Euclidean computational geometry

Figure 2.a — Figure2: Left: 3D mesh of a gyroid (triply periodic surface) 61. Right: Simulation of a periodic Delaunay triangulation of the hyperbolic plane 32.

Figure 2.b — Figure2: Left: 3D mesh of a gyroid (triply periodic surface) 61. Right: Simulation of a periodic Delaunay triangulation of the hyperbolic plane 32.

Triangulations, in particular Delaunay triangulations, in the Euclidean space $ℝ^{d}$ have been extensively studied throughout the 20th century and they are still a very active research topic. Their mathematical properties are now well understood, many algorithms to construct them have been proposed and analyzed (see the book of Aurenhammer et al.30). Some members of Gamble have been contributing to these algorithmic advances (see, e.g. 35, 68, 48, 34); they have also contributed robust and efficient triangulation packages through the state-of-the-art Computational Geometry Algorithms Library Cgal whose impact extends far beyond computational geometry. Application fields include particle physics, fluid dynamics, shape matching, image processing, geometry processing, computer graphics, computer vision, shape reconstruction, mesh generation, virtual worlds, geophysics, and medical imaging.3

It is fair to say that little has been done on non-Euclidean spaces, in spite of the large number of questions raised by application domains. Needs for simulations or modeling in a variety of domains4 ranging from the infinitely small (nuclear matter, nano-structures, biological data) to the infinitely large (astrophysics) have led us to consider 3D periodic Delaunay triangulations, which can be seen as Delaunay triangulations of the 3D flat torus, i.e., the quotient of $ℝ^{3}$ under the action of some group of translations 41. This work has already yielded a fruitful collaboration with astrophysicists 55, 69 and new collaborations with physicists are emerging. To the best of our knowledge, our Cgal package 40 is the only publicly available software that computes Delaunay triangulations of a 3D flat torus, in the special case where the domain is cubic. This case, although restrictive, is already useful.5 We have also generalized this algorithm to the case of general $d$ -dimensional compact flat manifolds 42. As far as non-compact manifolds are concerned, past approaches, limited to the two-dimensional case, have stayed theoretical 60.

Interestingly, even for the simple case of triangulations on the sphere, the software packages that are currently available are far from offering satisfactory solutions in terms of robustness and efficiency 39.

Moreover, while our solution for computing triangulations in hyperbolic spaces can be considered as ultimate 32, the case of hyperbolic manifolds has hardly been explored. Hyperbolic manifolds are quotients of a hyperbolic space by some group of hyperbolic isometries. Their triangulations can be seen as hyperbolic periodic triangulations. Periodic hyperbolic triangulations and meshes appear for instance in geometric modeling 64, neuromathematics 44, or physics 65. Even the case of the Bolza surface (a surface of genus 2, whose fundamental domain is the regular octagon in the hyperbolic plane) shows mathematical difficulties 337.

3.3 Probability in computational geometry

In most computational geometry papers, algorithms are analyzed in the worst-case setting. This often yields too pessimistic complexities that arise only in pathological situations that are unlikely to occur in practice. On the other hand, probabilistic geometry provides analyses with great precision 62, 63, 38, but using hypotheses with much more randomness than in most realistic situations. We are developing new algorithmic designs improving state-of-the-art performance in random settings that are not overly simplified and that can thus reflect many realistic situations.

Sixteen years ago, smooth analysis was introduced by Spielman and Teng analyzing the simplex algorithm by averaging on some noise on the data 67 (and they won the Gödel prize). In essence, this analysis smoothes the complexity around worst-case situations, thus avoiding pathological scenarios but without considering unrealistic randomness. In that sense, this method makes a bridge between full randomness and worst case situations by tuning the noise intensity. The analysis of computational geometry algorithms within this framework is still embryonic. To illustrate the difficulty of the problem, we started working in 2009 on the smooth analysis of the size of the convex hull of a point set, arguably the simplest computational geometry data structure; then, only one very rough result from 2004 existed 45 and we only obtained in 2015 breakthrough results, but still not definitive 47, 46, 53.

Another example of a problem of different flavor concerns Delaunay triangulations, which are rather ubiquitous in computational geometry. When Delaunay triangulations are computed for reconstructing meshes from point clouds coming from 3D scanners, the worst-case scenario is, again, too pessimistic and the full randomness hypothesis is clearly not adapted. Some results exist for “good samplings of generic surfaces” 29 but the big result that everybody wishes for is an analysis for random samples (without the extra assumptions hidden in the “good” sampling) of possibly non-generic surfaces.

Trade-offs between full randomness and worst case may also appear in other forms such as dependent distributions, or random distributions conditioned to be in some special configurations. In particular, simulating geometric distributions with repulsive properties, such as the determinantal point process, is currently out of reach for more than a few hundred points 56. Yet it has practical applications in physics to simulate particules with repulsion such as electrons 59, to simulate the distribution of network antennas 31, or in machine learning 57.

3.4 Discrete geometric structures

Our work on discrete geometric structures develops in several directions, each one probing a different type of structure. Although these objects appear unrelated at first sight, they can be tackled by the same set of probabilistic and topological tools.

A first research topic is the study of Order types. Order types are combinatorial encodings of finite (planar) point sets, recording for each triple of points the orientation (clockwise or counterclockwise) of the triangle they form. This already determines properties such as convex hulls or half-space depths, and the behaviour of algorithms based on orientation predicates. These properties for all (infinitely many) $n$ -point sets can be studied through the finitely many order types of size $n$ . Yet, this finite space is poorly understood: its estimated size leaves an exponential margin of error, no method is known to sample it without concentrating on a vanishingly small corner, the effect of pattern exclusion or VC dimension-type restrictions are unknown. These are all directions we actively investigate.

A second research topic is the study of Embedded graphs and simplicial complexes. Many topological structures can be effectively discretized, for instance combinatorial maps record homotopy classes of embedded graphs and simplicial complexes represent a large class of topological spaces. This raises many structural and algorithmic questions on these discrete structures; for example, given a closed walk in an embedded graph, can we find a cycle of the graph homotopic to that walk? (The complexity status of that problem is unknown.) Going in the other direction, some purely discrete structures can be given an associated topological space that reveals some of their properties (e.g. the Nerve theorem for intersection patterns). An open problem is for instance to obtain fractional Helly theorems for set systems of bounded topological complexity.

Another research topic is that of Sparse inclusion-exclusion formulas. For any family of sets $A_{1}, A_{2}, ..., A_{n}$ , by the principle of inclusion-exclusion we have

1_{⋃_{i = 1}^{n} A_{i}} = \sum_{I \subseteq {1, 2, ..., n}} {(- 1)}^{| I | + 1} 1_{⋂_{i \in I} A_{i}}

where $1_{X}$ is the indicator function of $X$ . This formula is universal (it applies to any family of sets) but its number of summands grows exponentially with the number $n$ of sets. When the sets are balls, the formula remains true if the summation is restricted to the regular triangulation; we proved that similar simplifications are possible whenever the Venn diagram of the $A_{i}$ is sparse. There is much room for improvements, both for general set systems and for specific geometric settings. Another interesting problem is to combine these simplifications with the inclusion-exclusion algorithms developed, for instance, for graph coloring.

4 Application domains

Many domains of science can benefit from the results developed by Gamble. Curves and surfaces are ubiquitous in all sciences to understand and interpret raw data as well as experimental results. Still, the non-linear problems we address are rather basic and fundamental, and it is often difficult to predict the impact of solutions in that area. The short-term industrial impact is likely to be small because, on basic problems, industries have used ad hoc solutions for decades and have thus got used to it.

The example of our work on quadric intersection is typical: even though we were fully convinced that intersecting 3D quadrics is such an elementary/fundamental problem that it ought to be useful, we were the first to be astonished by the scope of the applications of our software 6 (which was the first and still is the only one —to our knowledge— to compute robustly and efficiently the intersection of 3D quadrics) which has been used by researchers in, for instance, photochemistry, computer vision, statistics, and mathematics. Our work on certified drawing of plane (algebraic) curves falls in the same category. It seems obvious that it is widely useful to be able to draw curves correctly (recall also that part of the problem is to determine where to look in the plane) but it is quite hard to come up with specific examples of fields where this is relevant. A contrario, we know that certified meshing is critical in mechanical-design applications in robotics, which is a non-obvious application field. There, the singularities of a manipulator often have degrees higher than 10 and meshing the singular locus in a certified way is currently out of reach. As a result, researchers in robotics can only build physical prototypes for validating, or not, the approximate solutions given by non-certified numerical algorithms.

The fact that several of our pieces of software for computing non-Euclidean triangulations had already been requested by users long before they become public in Cgal is a good sign for their wide future impact. This will not come as a surprise, since most of the questions that we have been studying followed from discussions with researchers outside computer science and pure mathematics. Such researchers are either users of our algorithms and software, or we meet them in workshops. Let us only mention a few names here. Rien van de Weijgaert 55, 69 (astrophysicist, Groningen, NL) and Michael Schindler 66 (theoretical physicist, ENSPCI, CNRS, France) used our software for 3D periodic weighted triangulations. Stephen Hyde and Vanessa Robins (applied mathematics and physics at Australian National University) used our package for 3D periodic meshing. Olivier Faugeras (neuromathematics, INRIA Sophia Antipolis) had come to us and mentioned his needs for good meshes of the Bolza surface 44 before we started to study them. Such contacts are very important both to get feedback about our research and to help us choose problems that are relevant for applications. These problems are at the same time challenging from the mathematical and algorithmic points of view. Note that our research and our software are generic, i.e., we are studying fundamental geometric questions, which do not depend on any specific application. This recipe has made the sucess of the Cgal library.

Probabilistic models for geometric data are widely used to model various situations ranging from cell phone distribution to quantum mechanics. The impact of our work on probabilistic distributions is twofold. On the one hand, our studies of properties of geometric objects built on such distributions will yield a better understanding of the above phenomena and has potential impact in many scientific domains. On the other hand, our work on simulations of probabilistic distributions will be used by other teams, more maths oriented, to study these distributions.

5 Highlights of the year

5.1 Awards

The CGAL project, in which we are deeply involved, received a SoCG Test of Time award. Monique Teillaud and Andreas Fabri (GeometryFactory) gave the (video) presentation at the award ceremony.

More information on the Inria website.

6 New software, platforms, open data

6.1 New software

6.1.1 pwpoly

Keywords:
Evaluation, Polynomial equations, Complex number
Functional Description:
This software uses a new approach to evaluate and find the roots of polynomials whose coefficients do not all have the same order of magnitude. In particular, after a quasi-linear pre-processing in degree, the evaluation at a point is done in logarithmic time in degree, with the same precision as the evaluation of the original polynomial done with floating-point arithmetic. Moreover, for a well-conditioned polynomial, the calculation of the approximate roots is also performed in quasi-linear time in degree.
Publication:
https://inria.hal.science/hal-03980098
Authors:
Remi Imbach, Guillaume Moroz
Contact:
Guillaume Moroz

7 New results

7.1 Non-Linear Computational Geometry

Participants: Laurent Dupont, Nuwan Herath Mudiyanselage, Sylvain Lazard, Guillaume Moroz, Marc Pouget.

7.1.1 Fast evaluation and root finding for polynomials with floating-point coefficients

Evaluating or finding the roots of a polynomial $f (z) = f_{0} + \dots + f_{d} z^{d}$ with floating-point number coefficients is a ubiquitous problem. By using a piecewise approximation of $f$ obtained with a careful use of the Newton polygon of $f$ , we improved state-of-the-art upper bounds on the number of operations to evaluate and find the roots of a polynomial. In particular, if the coefficients of $f$ are given with $m$ significant bits, we provided for the first time an algorithm that finds all the roots of $f$ with a relative condition number lower than $2^{m}$ , using a number of bit operations quasi-linear in the bit-size of the floating-point representation of $f$ . Notably, our new approach handles efficiently polynomials with coefficients ranging from $2^{- d}$ to $2^{d}$ , both in theory and in practice. This work was published at the ISSAC 2024 conference 16 and led to the developpement of the software pwpoly that is in the process of being included in Maple 2024.

7.1.2 Fast high-resolution drawing of algebraic curves and surfaces

We addressed the problem of computing a drawing of high resolution of a plane curve defined by a bivariate polynomial equation $P (x, y) = 0$ . Given a grid of fixed resolution, a drawing is a subset of pixels. Our goal is to compute an approximate drawing that (i) contains all the parts of the curve that intersect the pixel edges, (ii) excludes a pixel when the evaluation of $P$ with interval arithmetic on each of its four edges does not contain zero. Most state-of-the-art approaches focus on bounding the number of independent evaluations. One of the challenges for computing drawings of high degree curves on a high-resolution grid is to minimize the complexity due to the many evaluations of the input polynomial. Using state-of-the-art Computer Algebra techniques, we designed new algorithms that amortize the evaluations and improve the complexity for computing such drawings. Our main contribution was to use a non-uniform grid based on the Chebyshev nodes to take advantage of multipoint evaluation techniques via the Discrete Cosine Transform. This work was the topic of Nuwan Herath's PhD thesis 19.

7.2 Non-Euclidean Computational Geometry

Participants: Vincent Despré, Loïc Dubois, Camille Lanuel, Alba Marina Málaga Sabogal, Monique Teillaud.

7.2.1 Computing a Dirichlet domain for a hyperbolic surface

This paper exhibits and analyzes an algorithm that takes a given closed orientable hyperbolic surface and outputs an explicit Dirichlet domain. The input is a fundamental polygon with side pairings. While grounded in topological considerations, the algorithm makes key use of the geometry of the surface. We introduce data structures that reflect this interplay between geometry and topology and show that the algorithm runs in polynomial time, in terms of the initial perimeter and the genus of the surface 15.

In collaboration with Benedikt Kolbe (now at University of Bonn) and Hugo Parlier (University of Luxembourg).

7.2.2 A linear bound for the Colin de Verdière parameter for graphs embedded on a surfaces

The Colin de Verdière graph parameter $μ (G)$ was introduced in 1990 by Y. Colin de Verdière. It is defined via spectral properties of a certain type of matrices, called Schrödinger operators, associated to a graph $G$ . We provide a combinatorial and self-contained proof that for all graphs $G$ embedded on a surface $S$ , the Colin de Verdière parameter $μ (G)$ is upper bounded by $7 - 2 χ (S)$ , where $χ (S)$ is the Euler characteristic of $S$ 17, 24.

In collaboration with Francis Lazarus (CNRS, G-SCOP) and Rudi Pendavingh ( TU/e - Eindhoven University of Technology).

7.2.3 Untangling Graphs on Surfaces

Consider a graph drawn on a surface (for example, the plane minus a finite set of obstacle points), possibly with crossings. We provide an algorithm to decide whether such a drawing can be untangled, namely, if one can slide the vertices and edges of the graph on the surface (avoiding the obstacles) to remove all crossings; in other words, whether the drawing is homotopic to an embedding. While the problem boils down to planarity testing when the surface is the sphere or the disk (or equivalently the plane without any obstacle), the other cases have never been studied before, except when the input graph is a cycle, in an abundant literature in topology and more recently by Despré and Lazarus [SoCG 2017, J. ACM 2019], who gave a near-linear algorithm for this problem. Our algorithm runs in $O (m + (g + b) n log n)$ time, where $g \geq 0$ and $b \geq 0$ are the genus and the number of boundary components of the input orientable surface $Σ$ , and $n$ is the size of the input graph drawing, lying on some fixed graph of size $m$ cellularly embedded on $Σ$ 22.

In collaboration with Éric Colin de Verdière (CNRS, Laboratoire d'Informatique Gaspard-Monge).

7.2.4 Unique ergodicity for infinite area Translation Surfaces

We consider infinite staircase translation surfaces with varying step sizes. We show that for typical step sizes, up to scaling, the translation flow has a unique invariant, non-atomic, ergodic Radon measure in almost every direction 25.

In collaboration with Serge Troubetzkoy (Institut de Mathématiques de Marseille).

7.3 Probabilistic Analysis of Geometric Data Structures and Algorithms

Participants: Olivier Devillers, Xavier Goaoc.

7.3.1 Two Lower Bounds for Random Point Sets via Negative Association

We present two lower bounds that hold with high probability for random point sets. We first give a new, and elementary, proof that the classical models of random point sets (uniform in a smooth convex body, uniform in a polygon, Gaussian) have a superconstant number of extreme points with high probability. We next prove that any algorithm that determines the orientation of all triples in a planar set of $n$ points (that is, the order type of the point set) from their Cartesian coordinates must read with high probability $4 n log n - O (n log log n)$ coordinate bits. This matches previously known upper bounds. Both bounds rely on a method due to Dubhashi and Ranjan 49 for obtaining concentration results via a negative association property 20.

In collaboration with Denys Bulavka (Charles University, Prague) , Philippe Duchon (LaBRI, Bordeaux), and Marc Glisse (Inria-DATASHAPE).

7.4 Discrete Geometric structures

Participants: Florent Koechlin, Xavier Goaoc, Sarah Wajsbrot.

7.4.1 Convex hulls of random order types

We establish the following two main results on order types of points in general position in the plane (realizable simple planar order types, realizable uniform acyclic oriented matroids of rank 3):

(a) The number of extreme points in an $n$ -point order type, chosen uniformly at random from all such order types, is on average $4 + o (1)$ . For labeled order types, this number has average $4 - \frac{8}{n^{2} - n + 2}$ and variance at most 3.

(b) The (labeled) order types read off a set of $n$ points sampled independently from the uniform measure on a convex planar domain, smooth or polygonal, or from a Gaussian distribution are concentrated, i.e., such sampling typically encounters only a vanishingly small fraction of all order types of the given size.

Result (a) generalizes to arbitrary dimension $d$ for labeled order types with the average number of extreme points $2 d + o (1)$ and constant variance. We also discuss to what extent our methods generalize to the abstract setting of uniform acyclic oriented matroids. Moreover, our methods show the following relative of the Erdős-Szekeres theorem: for any fixed $k$ , as $n \to \infty$ , a proportion $1 - O (1 / n)$ of the $n$ -point simple order types contain a triangle enclosing a convex $k$ -chain over an edge.

For the unlabeled case in (a), we prove that for any antipodal, finite subset of the two-dimensional sphere, the group of orientation preserving bijections is cyclic, dihedral, or one of $A_{4}$ , $S_{4}$ , or $A_{5}$ (and each case is possible). These are the finite subgroups of $S O (3)$ and our proof follows the lines of their characterization by Felix Klein. This work appeared in the Journal of the ACM 13.

In collaboration with Emo Welzl (ETH Zürich).

7.4.2 Some new results on geometric transversals

We investigate a number of questions, problems, and conjectures related to geometric transversal theory. Among our results we disprove a conjecture of Bárány and Kalai regarding weak $ϵ$ -nets for $k$ -flats and convex sets in $ℝ^{d}$ and we prove a conjecture of Arocha, Bracho, and Montejano regarding a colorful version of the Goodman–Pollack–Wenger transversal theorem. We also investigate the connected components of the space of line transversals to pairwise disjoint convex sets in $ℝ^{3}$ and we extend a theorem of Karasev and Montejano regarding colorful intersections and $k$ -transversals. This work was accepted for publication in Discrete & Computational Geometry 12.

In collaboration with Otfried Cheong (SCALGO) and Andreas Holmsen (KAIST).

7.4.3 A Canonical Tree Decomposition for Chirotopes

We introduce and study a notion of decomposition of planar point sets (or rather of their chirotopes) as trees decorated by smaller chirotopes. This decomposition is based on the concept of mutually avoiding sets, and adapts in some sense the modular decomposition of graphs in the world of chirotopes. The associated tree always exists and is unique up to some appropriate constraints. We also show how to compute the number of triangulations of a chirotope efficiently, starting from its tree and the (weighted) numbers of triangulations of its parts.

In collaboration with Mathilde Bouvel (INRIA project Team MOCQUA) and Valentin Feray (IECL, Nancy).

7.5 Miscellaneous

Participant: Olivier Devillers, Sylvain Lazard.

7.5.1 SCARST: Schnyder Compact And Regularity Sensitive Triangulation Data Structure.

We consider the problem of designing fast and compact solutions for representing the connectivity information of triangle meshes. While traditional data structures (Half-Edge, Corner Table) are fast and user-friendly, they tend to be memory-expensive. On the other hand, compression schemes, while meeting information-theory lower bounds, lack the ability to facilitate rapid navigation within the mesh structure. Compact representations provide an advantageous balance for representing large meshes, enabling a judicious compromise between memory consumption and fast implementation of navigational operations. We propose new representations that are sensitive to the regularity of the graph while still having worst case guarantees. For all our data structures we have both an interesting storage cost, typically 2 or 3 r.p.v. (references/vertex) in the case of very regular triangulations and provable upper bounds in the worst case scenario. One of our solution has a worst case cost of 3.33 r.p.v. which is currently the best-known bound improving the previous 4 r.p.v. 28. In terms of running time, our representations are slightly slower (factor 1.5 to 4) than classical data structures. In our experiments we compare on various meshes runtime and memory performance of our representations with those of the most efficient existing solutions 21.

In collaboration with Luca Castelli Aleardi (LIX)

7.5.2 Drawing Kn in Three Dimensions with One Bend per Edge

We present a drawing of $K_{n}$ in three dimensions in which vertices are placed at integer grid points and edges are drawn crossing-free with at most one bend per edge; the bend points are also placed at integer grid points. The drawing is determined by an incremental algorithm and the observed behavior of the algorithm produces an output of volume close to quadratic 23, 26.

8 Bilateral contracts and grants with industry

8.1 Bilateral contracts with industry

8.1.1 Waterloo Maple Inc.

Participants: Laurent Dupont, Sylvain Lazard, Guillaume Moroz, Marc Pouget, Rémi Imbach.

Company: Waterloo Maple Inc.

Duration: 2 years, renewable

Participants: Gamble and Ouragan Inria teams

Abstract: A renewable two-years licence and cooperation agreement was signed on April 1st, 2018 between Waterloo Maple Inc., Ontario, Canada (represented by Laurent Bernardin, its Executive Vice President Products and Solutions) and Inria. On the Inria side, this contract involves the teams Gamble and Ouragan (Paris), and it is coordinated by Fabrice Rouillier (Ouragan).

F. Rouillier and Gamble are the developers of the Isotop software for the computation of topology of curves. The transfer of a version of Isotop to Waterloo Maple Inc. should be done on the long run.

This contract was amended last year to include the new software hefroots for the isolation of the complex roots of a univariate polynomial. The transfer of hefroots to Waterloo Maple Inc. started at the end of 2021 with the help of the independent contractor Rémi Imbach. Rémi Imbach was then hired for one year by Inria through the ADT program. This led to the inclusion of hefroots in Maple 2023, and to the development of a improved software pwpoly that is planned to be included in Maple 2024.

8.1.2 GeometryFactory

Participants: Monique Teillaud.

Company: GeometryFactory

Duration: permanent

Participants: Inria and GeometryFactory

Abstract: Cgal packages developed in Gamble are commercialized by GeometryFactory.

9 Partnerships and cooperations

9.1 International initiatives

9.1.1 Inria associate team not involved in an IIL or an international program

FIP

Title:
Finite point sets and Intersection Patterns
Duration:
January 2021 to December 2023
Coordinators:
Xavier Goaoc and Andreas Holmsen (andreash@kaist.edu)
Partners:
- Korea Advanced Institute of Science and Technology Daejeon (Corée du Sud)
Inria contact:
Xavier Goaoc
Summary:
This project tackles two families of problems in discrete and computational geometry, dealing respectively with finite point sets and to intersection patterns of geometric set systems. The two PI already collaborate on one family of problems and have worked independently on the other. The goal of the associate team is to broaden this two-person collaboration, and help the emergence of new research groups.

9.1.2 ANR PRCI

ANR SoS

Title:
Structures on Surfaces
Duration:
4 years + 1 year Covid'19 extension
Starting date:
April 1st, 2018
Coordinator:
Monique Teillaud
Partners:
- Gamble project-team, Inria.
- LIGM (Laboratoire d'Informatique Gaspard Monge), Université Gustave Eiffel. Local Coordinator: Éric Colin de Verdière.
- RMATH (Mathematics Research Unit), University of Luxembourg. National Coordinator: Hugo Parlier.
Inria contact:
Monique Teillaud
Summary:

SoS is co-funded by ANR (ANR-17-CE40-0033) and FNR (INTER/ANR/16/11554412/SoS) as a PRCI (Projet de Recherche Collaborative Internationale).

The central theme of this project is the study of geometric and combinatorial structures related to surfaces and their moduli. Even though they work on common themes, there is a real gap between communities working in geometric topology and computational geometry and SoS aims to create a long-lasting bridge between them. Beyond a common interest, techniques from both ends are relevant and the potential gain in perspective from long-term collaborations is truly thrilling.

In particular, SoS aims to extend the scope of computational geometry, a field at the interface between mathematics and computer science that develops algorithms for geometric problems, to a variety of unexplored contexts. During the last two decades, research in computational geometry has gained wide impact through CGAL, the Computational Geometry Algorithms Library. In parallel, the needs for non-Euclidean geometries are arising, e.g., in geometric modeling, neuromathematics, or physics. Our goal is to develop computational geometry for some of these non-Euclidean spaces and make these developments readily available for users in academia and industry.

To reach this aim, SoS follows an interdisciplinary approach, gathering researchers whose expertise cover a large range of mathematics, algorithms and software. A mathematical study of the objects considered is performed, together with the design of algorithms when applicable. Algorithms are analyzed both in theory and in practice after prototype implementations, which are improved whenever it makes sense to target longer-term integration into CGAL.

Our main objects of study are Delaunay triangulations and circle patterns on surfaces, polyhedral geometry, and systems of disjoint curves and graphs on surfaces.
Workshop
An SoS retreat was organized at Schloss Dagstuhl (Jan 30 - Feb 03).
Project website:
sos.loria.fr

9.2 International research visitors

9.2.1 Visits of international scientists

Andreas Holmsen, Professor, KAIST (June 23rd – July 18th),
Boris Bukh, Professor, Carnegie Mellon University (July 1–8),
Denys Bulavka, PhD student, Charles University, Prague (August 21–25),
Jean Cardinal, Professor, Université Libre de Bruxelles (October 26–27).

9.2.2 Visits to international teams

Research stays abroad

Vincent Despre , Loîc Dubois , and Monique Teillaud visited EPFL for one week and worked with Peter Buser, together with Hugo Parlier (University of Luxembourg).

9.3 National initiatives

9.3.1 ANR PRC

ANR MIN-MAX

Title:
MIN-MAX
Duration:
2019 to 2023
Coordinator:
Stéphane Sabourau (Université Paris-Est Créteil)
Partners:
- Université Paris Est Créteil, Laboratoire d'Analyse et de Mathématiques Appliquées (LAMA). Local coordinator: Stéphane Sabourau
- Université de Tours, Institut Denis Poisson. Local coordinator: Laurent Mazet. This node includes two participants from Nancy, Benoît Daniel (IECL) and Xavier Goaoc (Loria, Gamble).
Inria contact:
Xavier Goaoc
Summary:

The MinMax projet is funded by ANR under number ANR-19-CE40-0014

This collaborative research project aims to bring together researchers from various areas – namely, geometry and topology, minimal surface theory and geometric analysis, and computational geometry and algorithms – to work on a precise theme around min-max constructions and waist estimates.
Projetc website:
perso.math.u-pem.fr/sabourau.stephane/min-max/

10 Dissemination

10.1 Promoting scientific activities

10.1.1 Scientific events: selection

Reviewer

All members of the team are regular reviewers for the conferences of our field, namely Symposium on Computational Geometry (SoCG), European Symposium on Algorithms (ESA), Symposium on Discrete Algorithms (SODA), International Symposium on Symbolic and Algebraic Computation (ISSAC), etc.

10.1.2 Journal

Member of the editorial boards

Monique Teillaud is a managing editor of JoCG, Journal of Computational Geometry.

Reviewer - reviewing activities

All members of the team are regular reviewers for the journals of our field, namely Discrete and Computational Geometry (DCG), Journal of Computational Geometry (JoCG), International Journal on Computational Geometry and Applications (IJCGA), Journal on Symbolic Computations (JSC), SIAM Journal on Computing (SICOMP), Mathematics in Computer Science (MCS), etc.

10.1.3 Software Project

Member of the Editorial Boards

Marc Pouget and Monique Teillaud are members of the CGAL editorial board.

10.1.4 Invited talks

Monique Teillaud gave a keynote talk “The CGAL project” at the 31st International Symposium on Graph Drawing and Network Visualization (September, Palermo) 14.

Guillaume Moroz gave an invited talk "Efficient approximation of polynomials" at Rencontres Arithmétiques du GdR Informatique Mathématique (October, Nancy).

Guillaume Moroz gave an invited talk at the workshop Fundamental Algorithms and Algorithmic Complexity (September).

Monique Teillaud was invited to be a speaker at the workshop Renormalization, computation and visualization in Geometry, Number Theory and Dynamics (September, CIRM): “Triangulations, CGAL, and hyperbolic surfaces” 18.

10.1.5 Research administration

Team members are involved in various committees managing the scientific life of the lab or at a national level.

Local

INRIA Comission Information et Édition Scientifique (Laurent Dupont ),
Fédération Charles Hermite (Xavier Goaoc ),
INRIA Comité de centre (Xavier Goaoc ),
LORIA Conseil scientifique (Sylvain Lazard ),
LORIA department chair (Sylvain Lazard ),
LORIA associate director (Sylvain Lazard ),
Computer science board in the École doctorale IAEM (Sylvain Lazard ),
INRIA Comité des utilisateurs des moyens informatiques (chair, Guillaume Moroz )
INRIA Commission de développement technologique (Guillaume Moroz ),
CLHSCT (Guillaume Moroz ),
INRIA PhD and postdoc hiring committee (Marc Pouget ),
LORIA Conseil de laboratoire (Monique Teillaud ),
Co-organization of “Tutotechno” (Monique Teillaud ),
Setting up a mentoring action at LORIA (Monique Teillaud ).

National

INRIA Mission Jeunes Chercheurs (chair, Sylvain Lazard ).

Hiring Committees

Olivier Devillers chaired the hiring committee for a Professor position at Polytech (Université de Lorraine).
Monique Teillaud was a member of the hiring committee for a Professor position at Université Gustave Eiffel in Marne-la-Vallée.
Guillaume Moroz was a member of the hiring committee for CRCN/ISFP positions at Inria Nancy Grand Est in 2023.

Evaluation Committees

HCERES committee for DIENS ENS Paris (Sylvain Lazard ).

10.1.6 Teaching Committees

Vincent Despre : Head of the Engineer diploma speciality SIR, Systèmes d'Information et Réseaux, Polytech Nancy, Université de Lorraine.
Laurent Dupont is the secretary of Commission Pédagogique Nationale Carrières Sociales / Information-Communication / Métiers du Multimédia et de l'Internet (2017-2022).
Laurent Dupont represents the Commission Pédagogique Nationale Carrières Sociales / Information-Communication / Métiers du Multimédia et de l'Internet at the national working group on D.U.T/B.U.T reform.
Laurent Dupont : Head of the Bachelor diploma Licence Professionnelle Animateur, Facilitateur de Tiers-lieux Eco-Responsables, Université de Lorraine.
Laurent Dupont : Responsible of fablab "Charlylab" of I.U.T. Nancy-Charlemagne,
Xavier Goaoc is the chair of the computer science department of l'École des Mines de Nancy.
Xavier Goaoc is a member of the Conseil d'administration de l'École des Mines de Nancy.

10.2 Teaching - Supervision - Juries

10.2.1 Teaching

Licence: Vincent Despre , Algorithmique, 44h, L2 PEIP, Polytech Nancy, France.
Licence: Vincent Despre , Programmation orientée objet, 84h, L3 IA2R, Polytech Nancy, France.
Master: Xavier Goaoc , Modèles d'environnements, planification de trajectoires, 12h, M2 AVR, Université de Lorraine, France (web).
Licence: Laurent Dupont , Web development, 45h, L1, Université de Lorraine, France.
Licence: Laurent Dupont , Web development, 150h, L2, Université de Lorraine, France.
Licence: Laurent Dupont , Web development and Social networks 70h L3, Université de Lorraine, France.
Licence: Laurent Dupont , 3D printing and CAO 40h, L3, Université de Lorraine, France.
Licence : Xavier Goaoc , Algorithms and complexity, 57 HETD, L3, École des Mines de Nancy, France.
Master: Xavier Goaoc , Computer architecture, 32 HETD, M1, École des Mines de Nancy Nancy, France.
Master: Xavier Goaoc , Introduction to blockchains, 32 HETD, M1, École des Mines de Nancy, France.
Licence: Alba Marina Malaga Sabogal , Information systems and databases, 86h, L1, Université de Lorraine, France.
Licence: Alba Marina Malaga Sabogal , Content Management Systems, 40h, L1, Université de Lorraine, France.
Master: Marc Pouget , Introduction to computational geometry, 10.5h, M2, École Nationale Supérieure de Géologie, France.

10.2.2 Supervision

PhD defended in June 2023: Nuwan Herath Mudiyanselage , Fast algorithm for the visualization of surfaces, supervised by Guillaume Moroz and Marc Pouget .
PhD in progress: Loïc Dubois , Untangling graphs on surfaces, started in Oct. 2022, supervised by Vincent Despre and Éric Colin de Verdière (Marne la Vallée).
PhD in progress: Camille Lanuel , A toolbox for hyperbolic surfaces, started in Oct. 2022, supervised by Vincent Despre and Monique Teillaud .
PhD in progress: Leo Valque , Rounding 3D meshes, started in Sept. 2020, supervised by Sylvain Lazard .
PhD in progress: Sarah Wajsbrot , Combinatorial convexity, its generalizations and applications to optimization, started in Oct. 2023, supervised by Xavier Goaoc .
Master internship M2: Marguerite Bin , Homological VC dimension following Kalai and Meshulam, started in Oct. 2023, supervised by Xavier Goaoc .

10.2.3 Juries

Xavier Goaoc chaired the PhD defense committee of Daria Pchelina, Université Sorbonne Paris Nord.
Xavier Goaoc was on the reading and defense committees of the PhD thesis of Theophile Buffière, Université Sorbonne Paris Nord.
Xavier Goaoc chaired the PhD defense committee of Guillaume Coiffier, Université de Lorraine.
Sylvain Lazard chaired the PhD defense committee of Jiayi Wei, École Polytechnique.
Sylvain Lazard chaired the PhD defense committee of Melike Aydinlilar, Université de Lorraine.
Marc Pouget was on the PhD defense committee of Christina Katsamaki, Sorbonne Université.
Monique Teillaud chaired the PhD defense committee of Djamel Eddine Amir, Université de Lorraine.

10.3 Popularization

Alba Málaga is a member of the scientific board for the association Les maths en scène and the marraine for a high-school math student club in Thionville, le labo Rosa Parks.

10.3.1 Education

Olivier Devillers presented research carreer in several different classes in highschool within the Chiche program.
Alba Málaga , for the Festival "Printemps des mathématiques" (23-25 mars 2025), coordinated and participated in a booth promoting sharing platforms for mathematical communication like Imaginary, or kits math.

10.3.2 Interventions

Alba Málaga gave two general audience talks for motivated high school students
- «Diplotores, une famille de tores plats polyèdraux» at the MATh.en.JEANS, annual east meeting, Mulhouse, 26/05/2023,
- a talk at the holiday workshop « Les maths, de l'Espace aux espaces » of the association Science Ouverte, Paris, 28/02/2023.

Alba Marina Malaga Sabogal and Laurent Dupont organized "Fabrikathon" in April 25, 26, 27, 28 at IUT Nancy-Charlemagne.

11 Scientific production

11.1 Major publications

1 articleN.Nicolas Chenavier and O.Olivier Devillers. Stretch Factor in a Planar Poisson-Delaunay Triangulation with a Large Intensity.Advances in Applied Probability5012018, 35-56HAL DOI
2 inproceedingsV.Vincent Despré, J.-M.Jean-Marc Schlenker and M.Monique Teillaud. Flipping Geometric Triangulations on Hyperbolic Surfaces.SoCG 2020 - 36th International Symposium on Computational GeometryZurich, Switzerland2020HAL DOI
3 articleO.Olivier Devillers, S.Sylvain Lazard and W.William Lenhart. Rounding meshes in 3D.Discrete and Computational GeometryApril 2020HAL DOI
4 articleX.Xavier Goaoc, P.Pavel Paták, Z.Zuzana Patáková, M.Martin Tancer and U.Uli Wagner. Shellability is NP-complete.Journal of the ACM (JACM)6632019HAL DOI
5 inproceedingsX.Xavier Goaoc and E.Emo Welzl. Convex Hulls of Random Order Types.SoCG 2020 - 36th International Symposium on Computational Geometry16436th International Symposium on Computational Geometry (SoCG 2020)Best paper awardZürich / Virtual, Switzerland2020, 49:1--49:15HAL DOI
6 articleR.Rémi Imbach, M.Marc Pouget and C.Chee Yap. Clustering Complex Zeros of Triangular Systems of Polynomials.Mathematics in Computer ScienceJune 2020HAL DOI
7 inproceedingsI.Iordan Iordanov and M.Monique Teillaud. Implementing Delaunay Triangulations of the Bolza Surface.33rd International Symposium on Computational Geometry (SoCG 2017)Brisbane, AustraliaJuly 2017, 44:1--44:15HAL DOI back to text
8 articleR.Ranjan Jha, D.Damien Chablat, L.Luc Baron, F.Fabrice Rouillier and G.Guillaume Moroz. Workspace, Joint space and Singularities of a family of Delta-Like Robot.Mechanism and Machine Theory127September 2018, 73-95HAL DOI
9 articleS.Sylvain Lazard, M.Marc Pouget and F.Fabrice Rouillier. Bivariate triangular decompositions in the presence of asymptotes.Journal of Symbolic Computation822017, 123--133HAL DOI back to text
10 inproceedingsG.Guillaume Moroz. New data structure for univariate polynomial approximation and applications to root isolation, numerical multipoint evaluation, and other problems.2021 IEEE 62nd Annual Symposimum on Foundations of Computer Science (FOCS)FOCS 2021 - 62nd Annual IEEE Symposimum on Foundations of Computer ScienceDenver, United StatesDecember 2021HAL DOI

11.2 Publications of the year

International journals

11 articleO.Otfried Cheong, O.Olivier Devillers, J.-W.Ji-Won Park and M.Marc Glisse. Covering families of triangles.Periodica Mathematica Hungarica872023, 86--109HAL DOI
12 articleO.Otfried Cheong, X.Xavier Goaoc and A.Andreas Holmsen. Some New Results on Geometric Transversals.Discrete and Computational GeometryNovember 2023HAL DOI back to text
13 articleX.Xavier Goaoc and E.Emo Welzl. Convex Hulls of Random Order Types.Journal of the ACM (JACM)701January 2023, 1-47HAL DOI back to text

Invited conferences

14 inproceedingsM.Monique Teillaud. The CGAL Project.31st International Symposium on Graph Drawing and Network VisualizationPalerme, ItalySeptember 2023HAL back to text

International peer-reviewed conferences

15 inproceedingsV.Vincent Despré, B.Benedikt Kolbe, H.Hugo Parlier and M.Monique Teillaud. Computing a Dirichlet Domain for a Hyperbolic Surface.Leibniz International Proceedings in Informatics (LIPIcs)39th International Symposium on Computational Geometry (SoCG 2023)Dallas, United StatesJune 2023, 27:1--27:15HAL DOI back to text
16 inproceedingsR.Rémi Imbach and G.Guillaume Moroz. Fast evaluation and root finding for polynomials with floating-point coefficients.ISSAC '23: Proceedings of the 2023 International Symposium on Symbolic and Algebraic ComputationISSAC 2023Tromsø, NorwayJuly 2023HAL back to text

Conferences without proceedings

17 inproceedingsC.Camille Lanuel, F.Francis Lazarus and R.Rudi Pendavingh. A linear bound for the Colin de Verdière parameter for graphs embedded on surfaces.EuroCG'23 (39th European Workshop on Computational Geometry)Barcelona, SpainMarch 2023HAL back to text
18 inproceedingsM.Monique Teillaud. Triangulations, CGAL, and hyperbolic surfaces.Renormalization, computation and visualization in Geometry, Number Theory and DynamicsMarseille (CIRM, Centre International de Rencontres Mathématiques), FranceSeptember 2023HAL back to text

Doctoral dissertations and habilitation theses

19 thesisN. H.Nuwan Herath Mudiyanselage. Fast high-resolution drawing of algebraic curves and surfaces.Université de LorraineJune 2023HAL back to text

Reports & preprints

20 miscD.Denys Bulavka, O.Olivier Devillers, P.Philippe Duchon, M.Marc Glisse and X.Xavier Goaoc. Two Lower Bounds for Random Point Sets via Negative Association.2023HAL back to text
21 miscL.Luca Castelli Aleardi and O.Olivier Devillers. SCARST: Schnyder Compact And Regularity Sensitive Triangulation Data Structure.2023HAL back to text
22 miscÉ.Éric Colin de Verdière, V.Vincent Despré and L.Loïc Dubois. Untangling Graphs on Surfaces.2023HAL DOI back to text
23 miscO.Olivier Devillers and S.Sylvain Lazard. Drawing $K_{n}$ in Three Dimensions with One Bend per Edge, revisited.2023HAL back to text
24 miscC.Camille Lanuel, F.Francis Lazarus and R.Rudi Pendavingh. A linear bound for the Colin de Verdière parameter for graphs embedded on surfaces.March 2023HAL back to text
25 miscA. M.Alba Marina Málaga Sabogal and S.Serge Troubetzkoy. Unique ergodicity for infinite area Translation Surfaces.July 2023HAL back to text

Other scientific publications

26 inproceedingsO.Olivier Devillers and S.Sylvain Lazard. One-Bend Drawing of $K_{n}$ in 3D, revisited.The 31st International Symposium on Graph Drawing and Network VisualizationPalermo, ItalySpringer2023HAL back to text
27 miscX.Xavier Goaoc and M.Michael Kerber. Guest Editors’ Foreword special issue of Discrete & Computational Geometry.November 2023HAL DOI

11.3 Cited publications

28 articleL. C.Luca Castelli Aleardi and O.Olivier Devillers. Array-based compact data structures for triangulations: Practical solutions with theoretical guarantees.J. Comput. Geom.912018, 247--289DOI back to text
29 inproceedingsD.Dominique Attali, J.-D.Jean-Daniel Boissonnat and A.André Lieutier. Complexity of the Delaunay triangulation of points on surfaces: the smooth case.Proceedings of the 19th Annual Symposium on Computational Geometry2003, 201--210URL: http://dl.acm.org/citation.cfm?id=777823DOI back to text
30 bookF.Franz Aurenhammer, R.Rolf Klein and D.-T.Der-Tsai Lee. Voronoi diagrams and Delaunay triangulations.World Scientific2013, URL: http://www.worldscientific.com/worldscibooks/10.1142/8685back to text
31 articleR.Rémi Bardenet, F.Frédéric Lavancier, X.Xavier Mary and A.Aurélien Vasseur. On a few statistical applications of determinantal point processes.ESAIM: Procs602017, 180-202URL: https://doi.org/10.1051/proc/201760180DOI back to text
32 articleM.Mikhail Bogdanov, O.Olivier Devillers and M.Monique Teillaud. Hyperbolic Delaunay complexes and Voronoi diagrams made practical.Journal of Computational Geometry52014, 56--85HAL back to text back to text
33 inproceedingsM.Mikhail Bogdanov, M.Monique Teillaud and G.Gert Vegter. Delaunay triangulations on orientable surfaces of low genus.Proceedings of the 32nd International Symposium on Computational Geometry2016, 20:1--20:15HAL DOI back to text
34 inproceedingsJ.-D.Jean-Daniel Boissonnat, O.Olivier Devillers and S.Samuel Hornus. Incremental construction of the Delaunay graph in medium dimension.Proceedings of the 25th Annual Symposium on Computational Geometry2009, 208--216HAL back to text
35 articleJ.-D.Jean-Daniel Boissonnat, O.Olivier Devillers, R.René Schott, M.Monique Teillaud and M.Mariette Yvinec. Applications of random sampling to on-line algorithms in computational geometry.Discrete and Computational Geometry81992, 51--71HAL back to text
36 techreportY.Yacine Bouzidi, S.Sylvain Lazard, G.Guillaume Moroz, M.Marc Pouget, F.Fabrice Rouillier and M.Michael Sagraloff. Improved algorithms for solving bivariate systems via Rational Univariate Representations.INRIAFebruary 2015HAL back to text
37 articleY.Yacine Bouzidi, S.Sylvain Lazard, M.Marc Pouget and F.Fabrice Rouillier. Separating linear forms and Rational Univariate Representations of bivariate systems.Journal of Symbolic Computation68May 2015, 84-119HAL DOI back to text
38 phdthesisP.Pierre Calka. Tessellations, convex hulls and Boolean model: some properties and connections.Université René Descartes - Paris V2009HAL back to text
39 inproceedingsM.Manuel Caroli, P. M.Pedro M. M. de Castro, S.Sébastien Loriot, O.Olivier Rouiller, M.Monique Teillaud and C.Camille Wormser. Robust and Efficient Delaunay Triangulations of Points on or Close to a Sphere.Proceedings of the 9th International Symposium on Experimental Algorithms6049Lecture Notes in Computer Science2010, 462--473HAL back to text
40 incollectionM.Manuel Caroli and M.Monique Teillaud. 3D Periodic Triangulations.CGAL User and Reference Manual3.5CGAL Editorial Board2009, URL: http://doc.cgal.org/latest/Manual/packages.html#PkgPeriodic3Triangulation3SummaryDOI back to text
41 inproceedingsM.Manuel Caroli and M.Monique Teillaud. Computing 3D Periodic Triangulations.Proceedings of the 17th European Symposium on Algorithms5757Lecture Notes in Computer Science2009, 59--70back to text
42 inproceedingsM.Manuel Caroli and M.Monique Teillaud. Delaunay Triangulations of Point Sets in Closed Euclidean $d$ -Manifolds.Proceedings of the 27th Annual Symposium on Computational Geometry2011, 274--282HAL DOI back to text
43 incollectionB.Bernard Chazelle and others. Application challenges to computational geometry: CG impact task force report.Advances in Discrete and Computational Geometry223Contemporary MathematicsProvidenceAmerican Mathematical Society1999, 407--463back to text
44 articleP.Pascal Chossat, G.Grégory Faye and O.Olivier Faugeras. Bifurcation of hyperbolic planforms.Journal of Nonlinear Science212011, 465--498URL: http://link.springer.com/article/10.1007/s00332-010-9089-3DOI back to text back to text
45 inproceedingsV.Valentina Damerow and C.Christian Sohler. Extreme points under random noise.Proceedings of the 12th European Symposium on Algorithms2004, 264--274URL: http://dx.doi.org/10.1007/978-3-540-30140-0_25DOI back to text
46 inproceedingsO.Olivier Devillers, M.Marc Glisse and X.Xavier Goaoc. Complexity analysis of random geometric structures made simpler.Proceedings of the 29th Annual Symposium on Computational GeometryJune 2013, 167-175HAL DOI back to text
47 inproceedingsO.Olivier Devillers, M.Marc Glisse, X.Xavier Goaoc and R.Rémy Thomasse. On the smoothed complexity of convex hulls.Proceedings of the 31st International Symposium on Computational GeometryLipics2015HAL DOI back to text
48 articleO.Olivier Devillers. The Delaunay hierarchy.International Journal of Foundations of Computer Science132002, 163-180HAL back to text
49 articleD.Devdatt Dubhashi and D.Desh Ranjan. Balls and Bins: A Study in Negative Dependence.Random Structures and Algorithms1321998, 99--124DOI back to text
50 articleL.Laurent Dupont, D.Daniel Lazard, S.Sylvain Lazard and S.Sylvain Petitjean. Near-Optimal Parameterization of the Intersection of Quadrics: III. Parameterizing Singular Intersections.Journal of Symbolic Computation4332008, 216--232HAL DOI back to text
51 articleL.Laurent Dupont, D.Daniel Lazard, S.Sylvain Lazard and S.Sylvain Petitjean. Near-optimal parameterization of the intersection of quadrics: I. The generic algorithm.Journal of Symbolic Computation4332008, 168--191HAL DOI back to text
52 articleL.Laurent Dupont, D.Daniel Lazard, S.Sylvain Lazard and S.Sylvain Petitjean. Near-optimal parameterization of the intersection of quadrics: II. A classification of pencils.Journal of Symbolic Computation4332008, 192--215HAL DOI back to text
53 articleM.Marc Glisse, S.Sylvain Lazard, J.Julien Michel and M.Marc Pouget. Silhouette of a random polytope.Journal of Computational Geometry712016, 14HAL back to text
54 articleM.Michael Hemmer, L.Laurent Dupont, S.Sylvain Petitjean and E.Elmar Schömer. A complete, exact and efficient implementation for computing the edge-adjacency graph of an arrangement of quadrics.Journal of Symbolic Computation4642011, 467-494HAL DOI back to text
55 inproceedingsJ.Johan Hidding, R.Rien van de Weygaert, G.Gert Vegter, B. J.Bernard J.T. Jones and M.Monique Teillaud. Video: the sticky geometry of the cosmic web.Proceedings of the 28th Annual Symposium on Computational Geometry2012, 421--422back to text back to text
56 articleJ. B.J. B. Hough, M.M. Krishnapur, Y.Y. Peres and B.B. Virág. Determinantal processes and independence.Probab. Surv.32006, 206-229back to text
57 articleA.Alex Kulesza and B.Ben Taskar. Determinantal Point Processes for Machine Learning.Foundations and Trends® in Machine Learning52–32012, 123-286URL: http://dx.doi.org/10.1561/2200000044DOI back to text
58 articleS.Sylvain Lazard, L.Lui sM. Peñaranda and S.Sylvain Petitjean. Intersecting quadrics: an efficient and exact implementation.Computational Geometry: Theory and Applications351-22006, 74--99HAL back to text
59 articleO.Odile Macchi. The coincidence approach to stochastic point processes.Advances in Applied Probability711975, 83–122DOI back to text
60 articleM.Marisa Mazón and T.Tomás Recio. Voronoi diagrams on orbifolds.Computational Geometry: Therory and Applications81997, 219--230back to text
61 miscA.Aymeric Pellé and M.Monique Teillaud. Periodic meshes for the CGAL library.Research NoteLondres, United Kingdom2014HAL back to text
62 articleA.Alfréd Rényi and R.Rolf Sulanke. Über die konvexe Hülle von $n$ zufällig gerwählten Punkten I.Z. Wahrsch. Verw. Gebiete21963, 75--84URL: http://dx.doi.org/10.1007/BF00535300DOI back to text
63 articleA.Alfréd Rényi and R.Rolf Sulanke. Über die konvexe Hülle von $n$ zufällig gerwählten Punkten II.Z. Wahrsch. Verw. Gebiete31964, 138--147URL: http://dx.doi.org/10.1007/BF00535973DOI back to text
64 inproceedingsG.Guodong Rong, M.Miao Jin and X.Xiaohu Guo. Hyperbolic centroidal Voronoi tessellation.Proceedings of the ACM Symposium on Solid and Physical Modeling2010, 117--126URL: http://dx.doi.org/10.1145/1839778.1839795DOI back to text
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GAMBLE - 2023

GAMBLE - 2023

2023Activity reportProject-TeamGAMBLE

Keywords

Computer Science and Digital Science

Other Research Topics and Application Domains

1 Team members, visitors, external collaborators

Research Scientists

Faculty Members

Post-Doctoral Fellow

PhD Students

Technical Staff

Interns and Apprentices

Administrative Assistant

External Collaborator

2 Overall objectives

3 Research program

3.1 Non-linear computational geometry

3.2 Non-Euclidean computational geometry

3.3 Probability in computational geometry

3.4 Discrete geometric structures

4 Application domains

5 Highlights of the year

5.1 Awards

6 New software, platforms, open data

6.1 New software

6.1.1 pwpoly

7 New results

7.1 Non-Linear Computational Geometry

7.1.1 Fast evaluation and root finding for polynomials with floating-point coefficients

7.1.2 Fast high-resolution drawing of algebraic curves and surfaces

7.2 Non-Euclidean Computational Geometry

7.2.1 Computing a Dirichlet domain for a hyperbolic surface

7.2.2 A linear bound for the Colin de Verdière parameter for graphs embedded on a surfaces

7.2.3 Untangling Graphs on Surfaces

7.2.4 Unique ergodicity for infinite area Translation Surfaces

7.3 Probabilistic Analysis of Geometric Data Structures and Algorithms

7.3.1 Two Lower Bounds for Random Point Sets via Negative Association

7.4 Discrete Geometric structures

7.4.1 Convex hulls of random order types

7.4.2 Some new results on geometric transversals

7.4.3 A Canonical Tree Decomposition for Chirotopes

7.5 Miscellaneous

7.5.1 SCARST: Schnyder Compact And Regularity Sensitive Triangulation Data Structure.

7.5.2 Drawing Kn in Three Dimensions with One Bend per Edge

8 Bilateral contracts and grants with industry

8.1 Bilateral contracts with industry

8.1.1 Waterloo Maple Inc.

8.1.2 GeometryFactory

9 Partnerships and cooperations

9.1 International initiatives

9.1.1 Inria associate team not involved in an IIL or an international program

FIP

9.1.2 ANR PRCI

ANR SoS

9.2 International research visitors

9.2.1 Visits of international scientists

9.2.2 Visits to international teams

Research stays abroad

9.3 National initiatives

9.3.1 ANR PRC

ANR MIN-MAX

10 Dissemination

10.1 Promoting scientific activities

10.1.1 Scientific events: selection

Reviewer

10.1.2 Journal

Member of the editorial boards

Reviewer - reviewing activities

10.1.3 Software Project

Member of the Editorial Boards

10.1.4 Invited talks

10.1.5 Research administration

Local

National

Hiring Committees

Evaluation Committees

10.1.6 Teaching Committees

10.2 Teaching - Supervision - Juries

10.2.1 Teaching