294 research outputs found
Equitable partition of graphs into induced forests
An equitable partition of a graph is a partition of the vertex-set of
such that the sizes of any two parts differ by at most one. We show that every
graph with an acyclic coloring with at most colors can be equitably
partitioned into induced forests. We also prove that for any integers
and , any -degenerate graph can be equitably
partitioned into induced forests.
Each of these results implies the existence of a constant such that for
any , any planar graph has an equitable partition into induced
forests. This was conjectured by Wu, Zhang, and Li in 2013.Comment: 4 pages, final versio
Long induced paths in graphs
We prove that every 3-connected planar graph on vertices contains an
induced path on vertices, which is best possible and improves
the best known lower bound by a multiplicative factor of . We
deduce that any planar graph (or more generally, any graph embeddable on a
fixed surface) with a path on vertices, also contains an induced path on
vertices. We conjecture that for any , there is a
contant such that any -degenerate graph with a path on vertices
also contains an induced path on vertices. We provide
examples showing that this order of magnitude would be best possible (already
for chordal graphs), and prove the conjecture in the case of interval graphs.Comment: 20 pages, 5 figures - revised versio
Small feedback vertex sets in planar digraphs
Let be a directed planar graph on vertices, with no directed cycle of
length less than . We prove that contains a set of vertices
such that has no directed cycle, and if ,
if , and if . This
improves recent results of Golowich and Rolnick.Comment: 5 pages, 1 figure - v3 final versio
Europe moins vieille que prévue : la démographie favorable à une politique de croissance.
Cette publication n'a pas de résumé
Real time estimation of potential output and output gap for theeuro-area: comparing production function with unobserved componentsand SVAR approaches
We develop a new version of the production function (PF) approach usually used for estimating the output gap of the euro area. Our version does not call for any (often imprecise) measure of the capital stock and improves the estimation of the trend total factor productivity. We asses this approach by comparing it with two other multivariate methods mostly used for output gap estimates, a multivariate unobserved components (MUC) model and a Structural Vector Auto-Regressive (SVAR) model. The comparison is conducted by relying on assessment criteria such as the concordance of the turning points chronology with a reference one, the inflation forecasting power and the real-time consistency of the estimates. Two contributions are achieved. Firstly, we take into account data revisions and their impact on the output gap estimates by using vintage datasets coming from the Euro Area Business Cycle (EABCN) Real-Time Data-Base (RTDB). Secondly, the PF approach, generally employed by policy-makers despite of its difficult implementation, is assessed. We thus improve on previous papers which limited their assessment on other multivariate methods, e.g. MUC or SVAR models. The different methods show different ranks in relation to the three criteria. This new PF estimate appears highly concordant with the reference chronology. Its forecasting power appears favourable only for the shortest horizon (1 month). Finally, the SVAR model appears more consistent in real-time.potential output, production function, state-space models, structural VARs
Nairu en zone heureuse
Cette Ă©tude spĂ©ciale propose des estimations du niveau non inflationniste du taux de chĂŽmage (Nairu) pour la zone euro agrĂ©gĂ©e, pour la France, lâItalie et lâAllemagne. Une Ă©quation dâinflation, qui dĂ©pend de lâĂ©cart du taux de chĂŽmage au Nairu, est estimĂ©e par le filtre de Kalman. Le modĂšle le plus simple, qui considĂšre le Nairu comme une marche alĂ©atoire, a des capacitĂ©s prĂ©dictives limitĂ©es. Il diagnostique un taux de chĂŽmage infĂ©rieur au Nairu Ă lâhorizon de notre prĂ©vision.
Il est confrontĂ© Ă une deuxiĂšme version qui fait dĂ©pendre lâĂ©volution du Nairu de celle du taux de chĂŽmage lui-mĂȘme. Ce lien, vĂ©rifiĂ© empiriquement pour tous les pays, est parfois interprĂ©tĂ© comme un phĂ©nomĂšne dâhystĂ©rĂšse. En identifiant un des dĂ©terminants du Nairu, ce modĂšle est mieux adaptĂ© en projection. De plus, cette spĂ©cification amĂšne Ă des prĂ©visions sensiblement plus basses du Nairu de long terme, Ă©cartant Ă moyen terme le risque inflationniste.The aim of this special study consists in estimating the non-accelerating inflation rate of unemployment (NAIRU) for the aggregated euro area, France, Italy and Germany. An equation, estimated with the Kalman filter, relates the inflation variation with the terms of trade and the gap between the unemployment and the Nairu. The basic model, where the Nairu is specified as a random walk, shows bad forecasting properties. With this model, the forecasted unemployment rate would become lower than the Nairu before 2008. Another model relates the Nairu with the unemployment rate. This relation is significant for all countries and is interpreted as a hysteresis effect. Moreover, this model forecasts lower values of the Nairu and, for this reason, we do not expect inflation tensions
Taux de chĂŽmage : la France fait-elle vraiment moins bien que ses voisins ?
Cette Ă©tude spĂ©ciale cherche Ă comprendre pourquoi les performances de taux de chĂŽmage en France sont globalement moins bonnes que celles de ses principaux voisins, surtout depuis 2005. MalgrĂ© une plus forte croissance Ă©conomique, le taux de chĂŽmage français a en effet progressĂ© de 0,4 point entre 2001 et 2007 alors quâil a reculĂ© de 0,4 et de 2,4 points en Allemagne et en Italie. Ce dĂ©calage sâexplique par le plus fort dynamisme de la population active française, mais aussi par les politiques de flexibilisation du marchĂ© du travail mises en Ćuvre en Allemagne et en Italie.
Les meilleures performances de ces deux derniers pays sont toutefois Ă relativiser car elles reposent principalement sur une prĂ©carisation de lâemploi et se sont traduites par une forte hausse de lâemploi temporaire et du travail Ă temps partiel subi. Si cette stratĂ©gie de flexibilisation conduit Ă des crĂ©ations dâemplois en pĂ©riode de reprise, ce gain pourrait disparaĂźtre au prochain ralentissement. Elle pose aussi le problĂšme de concentrer la flexibilitĂ© sur un segment de la population.
La premiĂšre partie classifie les politiques de lutte contre le chĂŽmage afin de comparer les stratĂ©gies adoptĂ©es dans les trois pays. Les trois suivantes dĂ©taillent les politiques mises en oeuvre dans chaque pays. La cinquiĂšme montre que les trois grands pays de la zone euro nâont pas adoptĂ© une stratĂ©gie homogĂšne de rĂ©duction du chĂŽmage
Potentiels moins freinés
Partant des estimations de la croissance potentielle de lâOCDE pour 2007, situĂ©es Ă 1,9 % pour la France, Ă 1,5 % pour lâAllemagne et Ă 1,3 % pour lâItalie, nous nous interrogeons sur le caractĂšre permanent ou non de ces divergences et sur lâimpact des rĂ©centes rĂ©visions de projection de population active sur ces potentiels. Il apparaĂźt que les mĂ©thodes dâestimation par filtrage de la croissance potentielle sont peu pertinentes en projection car elles consistent Ă extrapoler les Ă©volutions rĂ©centes de la population active et de la productivitĂ©. Or, ces deux variables sont souvent affectĂ©es par des phĂ©nomĂšnes transitoires.
Nous tentons de corriger ce biais de fin dâĂ©chantillon en intĂ©grant diverses hypothĂšses relatives aux principales variables dĂ©mographiques et Ă©conomiques qui sont cohĂ©rentes avec lâĂ©quilibre Ă moyen terme des systĂšmes de protection sociale. Ă lâhorizon 2050, on sâattend Ă un ralentissement de la croissance potentielle Ă 1,7 % pour la France et Ă 1,1 % pour lâAllemagne et lâItalie. Les rĂ©centes rĂ©visions en France et en Italie de projections dĂ©mographiques et de taux dâactivitĂ©, qui intĂšgrent notamment les rĂ©formes rĂ©centes des rĂ©gimes de retraite, permettraient respectivement une croissance supĂ©rieure de 0,3 et de 0,1 point en 2050 par rapport aux prĂ©cĂ©dentes projections.Basing upon OECDâs estimates of potential output growth for France (1.9%), Germany (1.5%) and Italy (1.3%), we investigate the permanent nature of such a divergence. Potential output estimates based on filtering techniques extrapolate temporary evolutions in productivity and labour force which may be irrelevant when projecting growth on a longer time horizon. We correct for this sampleâs end bias by using assumptions on the long term evolution of the main demographic and economic variables, which are consistent with the medium-term equilibrium of reformed social protection systems. Potential growth is expected to slow down to 1,7% by 2050 in France and to 1,1% in Germany and Italy. The most recent upward revisions of population growth in France and Italy account for respectively 0,3 and 0,1 point of higher growth in 2050 as compared to previous projections
SynteBase/SynteView: a tool to visualize gene order conservation in prokaryotic genomes
<p>Abstract</p> <p>Background</p> <p>It has been repeatedly observed that gene order is rapidly lost in prokaryotic genomes. However, persistent synteny blocks are found when comparing more or less distant species. These genes that remain consistently adjacent are appealing candidates for the study of genome evolution and a more accurate definition of their functional role. Such studies require visualizing conserved synteny blocks in a large number of genomes at all taxonomic distances.</p> <p>Results</p> <p>After comparing nearly 600 completely sequenced genomes encompassing the whole prokaryotic tree of life, the computed synteny data were assembled in a relational database, SynteBase. SynteView was designed to visualize conserved synteny blocks in a large number of genomes after choosing one of them as a reference. SynteView functions with data stored either in SynteBase or in a home-made relational database of personal data. In addition, this software can compute <it>on-the-fly </it>and display the distribution of synteny blocks which are conserved in pairs of genomes. This tool has been designed to provide a wealth of information on each positional orthologous gene, to be user-friendly and customizable. It is also possible to download sequences of genes belonging to these synteny blocks for further studies. SynteView is accessible through Java Webstart at <url>http://www.synteview.u-psud.fr</url>.</p> <p>Conclusion</p> <p>SynteBase answers queries about gene order conservation and SynteView visualizes the obtained results in a flexible and powerful way which provides a comparative overview of the conserved synteny in a large number of genomes, whatever their taxonomic distances.</p
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