- Marthe BonamyVendredi 3 juin 2016 à 11h, salle 24-25/405Argyris KalogeratosLundi 13 juin 2016 à 11h, salle 26-00/332Gilles TredanVendredi 24 juin 2016 à 11h, salle 24-25/405Sergey KirgizovLundi 04 juillet 2016 à 11h, salle 24-25/405Christophe PaulVendredi 08 juillet 2016 à 11h, salle 24-25/405
- affinity index algorithm analysis antipaedo attack bipartite blog network blogs capitalisme social Cascade centrality clustering communities community detection community structure complex network complex networks complex systems compression connected graphs data mining debian degree distribution degree peeling diameter diffusion diffusion phenomena distributed measurements DynamicNetworks dynamics edge-Markovian evolving graph eDonkey ego-centered ego-centered communities email epidemiology event detection evolving graphs evolving networks exploration failure fixed points formal concepts gossip graph graph algorithm graph decompositions Graphs hierarchical clustering honeypot influence influence ranking interaction networks internal links internet Internet topology intrinsic time IP-level ip exchanges lattice leaders link prediction long term communities markovian model measurement mesure d’influence metrics Metrology mobile networks Modelling modularity multi-ego-centered communities multi-scale multipartite graph network dynamics node proximity node similarity opinion dynamics outliers p2p P2P dynamics P2P networks parametric paris paris-traceroute path-vector routing pedophile activity phone power-law radar random graph random walks reachability robustness routing routing tables scale-free security simulation simulations sir social networks spreading spreading cascades stability statistical analysis stochastic process three-state cellular automata time-varying Topology traceroute triangles twitter UDP user profiles viral marketing visualization web wifi
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Kempe equivalence of colourings
Vendredi 3 juin 2016 à 11h, salle 24-25/405
Given a colouring of a graph, a Kempe change is the operation of picking a maximal bichromatic subgraph and switching the two colours in it. Two colourings are Kempe equivalent if they can be obtained from each other through a series of Kempe changes. Kempe changes were first introduced in a failed attempt to prove the Four Colour Theorem, but they proved to be a powerful tool for other colouring problems. They are also relevant for more applied questions, most notably in theoretical physics. Consider a graph with no vertex of degree more than some integer D. In 2007, Mohar conjectured that all its D-colourings are Kempe-equivalent. Feghali, Johnson and Paulusma proved in 2015 that this is true for D=3, with the exception of one single graph which disproves the conjecture in its generality. We settle the remaining cases by proving the conjecture holds for every integer D at least 4. This is a joint work with Nicolas Bousquet (LIRIS, Ecole Centrale Lyon, France), Carl Feghali (Durham University, UK) and Matthew Johnson (Durham University, UK).
Suppressing diffusion processes on arbitrary networks using treatment resources of limited efficiency
Lundi 13 juin 2016 à 11h, salle 26-00/332
In many real-life situations, it is critical to dynamically suppress or remove an undesired diffusion process (viruses, information, behaviors, etc.). The talk will present a framework for Dynamic Resource Allocation (DRA) assuming a continuous-time SIS epidemic model, and that a budget of treatment resources of limited efficiency are at the disposal of authorities. Special emphasis will be given on the macro- and microscopic (or local) properties of the network structure for the problem and two strategies will be presented that fall in this framework: a) a simple yet effective greedy approach, and b) a more sophisticated one that uses a precomputed priority plan of how the healing strategy should proceed on a specific network. Additionally, extensions in competitive scenarios will be discussed.
Temporal density of complex networks and ego-community dynamics
Lundi 04 julliet 2016 à 11h, salle 24-25/405
At first, we say that a ego-community structure is a probability measure defined on the set of network nodes. Any subset of nodes may engender its own ego-community structure around. Many community detection algorithms can be modified to yield a result of this type, for instance, the personalized pagerank. We also recall that community detection algorithms (including personalized pagerank) can be viewed from different perspectives: random walks, convergence of markov chain, spectral clustering, optimization, mincut(s), discrete cheeger inequality(ies), etc. Next, we present a continuous version of Viard-Latapy-Magnien link streams, that we call "temporal density". Classical kernel density estimation is used to move from discrete link streams towards their continuous counterparts. Using matrix perturbation theory we can prove that ego-community structure changes smoothly when the network evolves smoothly. This is very important, for example, for visualization purposes. Combining the temporal density and personalized pagerank methods, we are able to visualize and study the evolution of the ego-community structures of complex networks with a large number of temporal links in order to extract interacting information. For example, we can detect events, trace the evolution of (ego-)community structure, etc. We illustrate and validate our approach using "Primary school temporal network data" provided by sociopatterns.org, and we show how the temporal density can be applied to the study of very large datasets, such as a collection of tweets written by European Parliament candidates during European Parliament election in 2014.