An on-line competitive algorithm for coloring bipartite graphs without long induced paths

The existence of an on-line competitive algorithm for coloring bipartite graphs remains a tantalizing open problem. So far there are only partial positive results for bipartite graphs with certain small forbidden graphs as induced subgraphs. We propose a new on-line competitive coloring algorithm for $P_9$-free bipartite graphs

09171 Abstracts Collection -- Adaptive, Output Sensitive, Online and Parameterized Algorithms

From 19.01. to 24.04.2009, the Dagstuhl Seminar 09171 ``Adaptive, Output Sensitive, Online and Parameterized Algorithms \u27\u27 was held in Schloss Dagstuhl~--~Leibniz Center for Informatics. During the seminar, several participants presented their current research, and ongoing work and open problems were discussed. Abstracts of the presentations given during the seminar as well as abstracts of seminar results and ideas are put together in this paper. The first section describes the seminar topics and goals in general. Links to extended abstracts or full papers are provided, if available

Equation-free analysis of a dynamically evolving multigraph

In order to illustrate the adaptation of traditional continuum numerical techniques to the study of complex network systems, we use the equation-free framework to analyze a dynamically evolving multigraph. This approach is based on coupling short intervals of direct dynamic network simulation with appropriately-defined lifting and restriction operators, mapping the detailed network description to suitable macroscopic (coarse-grained) variables and back. This enables the acceleration of direct simulations through Coarse Projective Integration (CPI), as well as the identification of coarse stationary states via a Newton-GMRES method. We also demonstrate the use of data-mining, both linear (principal component analysis, PCA) and nonlinear (diffusion maps, DMAPS) to determine good macroscopic variables (observables) through which one can coarse-grain the model. These results suggest methods for decreasing simulation times of dynamic real-world systems such as epidemiological network models. Additionally, the data-mining techniques could be applied to a diverse class of problems to search for a succint, low-dimensional description of the system in a small number of variables

Spatially Ordered Treemaps

Existing treemap layout algorithms suffer to some extent from poor or inconsistent mappings between data order and visual ordering in their representation, reducing their cognitive plausibility. While attempts have been made to quantify this mismatch, and algorithms proposed to minimize inconsistency, solutions provided tend to concentrate on one-dimensional ordering. We propose extensions to the existing squarified layout algorithm that exploit the two-dimensional arrangement of treemap nodes more effectively. Our proposed spatial squarified layout algorithm provides a more consistent arrangement of nodes while maintaining low aspect ratios. It is suitable for the arrangement of data with a geographic component and can be used to create tessellated cartograms for geovisualization. Locational consistency is measured and visualized and a number of layout algorithms are compared. CIELab color space and displacement vector overlays are used to assess and emphasize the spatial layout of treemap nodes. A case study involving locations of tagged photographs in the Flickr database is described

Graph coloring techniques for planning dynamic optical networks

Dynamic optical networks will be crucial in global optical communications in the next 5-10 years.On-demand services, fuelled by applications such as cloud computing and grid computing, are the main drivers for the availability of an increasingly dynamic network infrastructure. Efficient network planning tools that deal with Routing and Wavelength Assignment problems are of paramount relevance in this dynamics cenario. In this work, a simulator for planning dynamic optical networks was developed, and several real networks were tested, such as National Science Foundation Network, British Telecom, US Backbone Network, and also bidirectional ring networks. In this simulator, we have implemented a graph coloring wavelength assignment algorithm named Small-Bucket algorithm that allows recoloring to occur. A comparison performance with the First-fit algorithm is performed in terms of the blocking probability, number of recolorings, number of colors used and simulation time. It is concluded that the Small-Bucket algorithm originate slower blocking probabilities than the ones obtained with the First-fit algorithm. However, to reach these low blocking probabilities, the Small-Bucket algorithm makes use of a larger number of wavelengths and recolorings.As redes ópticas dinâmicas serão cruciais nas comunicações ópticas globais nos proximos 5-10 anos. Os principais impulsionadores deste dinamismo são os serviços on-demand, suportados por aplicações como computação em nuvem e computação em grelha, conduzindo à necessidade de uma infraestrutura de rede cada vez mais dinâmica. Ferramentas de planeamento de rede eficientes, que lidam com os problemas de encaminhamento e atribuição de comprimentos de onda serão de extrema relevância neste cenário dinâmico. Neste trabalho foi desenvolvido um simulador para o planeamento de redes ópticas dinâmicas, e várias redes reais foram testadas, como a National Science Foundation Network, a British Telecom, a US Backbone Network e também redes bidirecionais em anel. Neste simulador, implementa-se um algoritmo de coloração de grafos denominado algoritmo Small-Bucket, que permite a ocorrência de recolorações de nós. Este algoritmo é comparado como algoritmo First-fit, em termos de probabilidade de bloqueio, número de recolorações, número de cores usadas e tempo de simulação. Conclui-se que o algoritmo Small-Bucket produz menores probabilidades de bloqueio do que as obtidas com o algoritmo First-fit. No entanto, para atingir essas baixas probabilidades de bloqueio, o algoritmo Small-Bucket faz uso de um maior número de comprimentos de onda e recolorações

Position and energy-resolved particle detection using phonon-mediated microwave kinetic inductance detectors

We demonstrate position and energy-resolved phonon-mediated detection of particle interactions in a silicon substrate instrumented with an array of microwave kinetic inductance detectors (MKIDs). The relative magnitude and delay of the signal received in each sensor allow the location of the interaction to be determined with ≲ 1mm resolution at 30 keV. Using this position information, variations in the detector response with position can be removed, and an energy resolution of σ_E = 0.55 keV at 30 keV was measured. Since MKIDs can be fabricated from a single deposited film and are naturally multiplexed in the frequency domain, this technology can be extended to provide highly pixelized athermal phonon sensors for ∼1 kg scale detector elements. Such high-resolution, massive particle detectors would be applicable to rare-event searches such as the direct detection of dark matter, neutrinoless double-beta decay, or coherent neutrino-nucleus scattering