MySemCloud: Semantic-aware Word Cloud Editing

Word clouds are a popular text visualization technique that summarize an input text by displaying its most important words in a compact image. The traditional layout methods do not take proximity effects between words into account; this has been improved in semantic word clouds, where relative word placement is controlled by edges in a word similarity graph. We introduce MySemCloud, a new human-in-the-loop tool to visualize and edit semantic word clouds. MySemCloud lets users perform computer-assisted local moves of words, which improve or at least retain the semantic quality. To achieve this, we construct a word similarity graph on which a system of forces is applied to generate a compact initial layout with good semantic quality. The force system also allows us to maintain these attributes after each user interaction, as well as preserve the user's mental map. The tool provides algorithmic support for the editing operations to help the user enhance the semantic quality of the visualization, while adjusting it to their personal preference. We show that MySemCloud provides high user satisfaction as well as permits users to create layouts of higher quality than state-of-the-art semantic word cloud generation tools.Comment: Appeared at PacificVis 202

The Complexity of Cluster Vertex Splitting and Company

Clustering a graph when the clusters can overlap can be seen from three different angles: We may look for cliques that cover the edges of the graph, we may look to add or delete few edges to uncover the cluster structure, or we may split vertices to separate the clusters from each other. Splitting a vertex $v$ means to remove it and to add two new copies of $v$ and to make each previous neighbor of $v$ adjacent with at least one of the copies. In this work, we study the underlying computational problems regarding the three angles to overlapping clusterings, in particular when the overlap is small. We show that the above-mentioned covering problem, which also has been independently studied in different contexts,is NP-complete. Based on a previous so-called critical-clique lemma, we leverage our hardness result to show that Cluster Editing with Vertex Splitting is also NP-complete, resolving an open question by Abu-Khzam et al. [ISCO 2018]. We notice, however, that the proof of the critical-clique lemma is flawed and we give a counterexample. Our hardness result also holds under a version of the critical-clique lemma to which we currently do not have a counterexample. On the positive side, we show that Cluster Vertex Splitting admits a vertex-linear problem kernel with respect to the number of splits.Comment: 30 pages, 9 figure

Turbocharging Heuristics for Weak Coloring Numbers

Bounded expansion and nowhere-dense classes of graphs capture the theoretical tractability for several important algorithmic problems. These classes of graphs can be characterized by the so-called weak coloring numbers of graphs, which generalize the well-known graph invariant degeneracy (also called k-core number). Being NP-hard, weak-coloring numbers were previously computed on real-world graphs mainly via incremental heuristics. We study whether it is feasible to augment such heuristics with exponential-time subprocedures that kick in when a desired upper bound on the weak coloring number is breached. We provide hardness and tractability results on the corresponding computational subproblems. We implemented several of the resulting algorithms and show them to be competitive with previous approaches on a previously studied set of benchmark instances containing 86 graphs with up to 183831 edges. We obtain improved weak coloring numbers for over half of the instances.Comment: 25 pages, 15 figure

Planarizing Graphs and their Drawings by Vertex Splitting

The splitting number of a graph $G=(V,E)$ is the minimum number of vertex splits required to turn $G$ into a planar graph, where a vertex split removes a vertex $v \in V$, introduces two new vertices $v_1, v_2$, and distributes the edges formerly incident to $v$ among its two split copies $v_1, v_2$. The splitting number problem is known to be NP-complete. In this paper we shift focus to the splitting number of graph drawings in $\mathbb R^2$, where the new vertices resulting from vertex splits can be re-embedded into the existing drawing of the remaining graph. We first provide a non-uniform fixed-parameter tractable (FPT) algorithm for the splitting number problem (without drawings). Then we show the NP-completeness of the splitting number problem for graph drawings, even for its two subproblems of (1) selecting a minimum subset of vertices to split and (2) for re-embedding a minimum number of copies of a given set of vertices. For the latter problem we present an FPT algorithm parameterized by the number of vertex splits. This algorithm reduces to a bounded outerplanarity case and uses an intricate dynamic program on a sphere-cut decomposition

La jeunesse scientifique d'Auvergne et de Rhône Alpes s'engage pour un nouvel ordre alimentaire mondial

Film présenté dans le cadre de l'Exposition Universelle de Milan en ItalieNous, jeunesse scientifique des régions Auvergne et Rhône-Alpes, déclarons solennellement notre implication dans la création et le développement d’un système agricole et alimentaire adapté aux futurs enjeux nutritionnels mondiaux. Conscients que nous sommes dans une course perpétuelle à la productivité, génératrice d’un risque pour les écosystèmes et la santé des hommes, nous souhaitons l’avènement d’un modèle alimentaire pérenne et garant d’un accès universel à une nourriture saine et respectueuse de l’environnement. Ce modèle doit être le moteur d’une équité sociale sans compromis, d’une sécurité alimentaire sans exception, et le faire-valoir de notre Terre que nous jugeons riche mais fragile. S’il s’agit de notre utopie aujourd’hui, cela doit être notre réalité de demain. Nous reconnaissons l’impasse devant laquelle notre modèle actuel de production, de distribution et de consommation se trouve. Le gaspillage colossal, les disparités croissantes et les problèmes de santé publique aujourd’hui à l’oeuvre doivent cesser

La jeunesse scientifique d'Auvergne et de Rhône Alpes s'engage pour un nouvel ordre alimentaire mondial

Film présenté dans le cadre de l'Exposition Universelle de Milan en ItalieNous, jeunesse scientifique des régions Auvergne et Rhône-Alpes, déclarons solennellement notre implication dans la création et le développement d’un système agricole et alimentaire adapté aux futurs enjeux nutritionnels mondiaux. Conscients que nous sommes dans une course perpétuelle à la productivité, génératrice d’un risque pour les écosystèmes et la santé des hommes, nous souhaitons l’avènement d’un modèle alimentaire pérenne et garant d’un accès universel à une nourriture saine et respectueuse de l’environnement. Ce modèle doit être le moteur d’une équité sociale sans compromis, d’une sécurité alimentaire sans exception, et le faire-valoir de notre Terre que nous jugeons riche mais fragile. S’il s’agit de notre utopie aujourd’hui, cela doit être notre réalité de demain. Nous reconnaissons l’impasse devant laquelle notre modèle actuel de production, de distribution et de consommation se trouve. Le gaspillage colossal, les disparités croissantes et les problèmes de santé publique aujourd’hui à l’oeuvre doivent cesser