55 research outputs found
b-coloring is NP-hard on co-bipartite graphs and polytime solvable on tree-cographs
Get PDFA b-coloring of a graph is a proper coloring such that every color class
contains a vertex that is adjacent to all other color classes. The b-chromatic
number of a graph G, denoted by \chi_b(G), is the maximum number t such that G
admits a b-coloring with t colors. A graph G is called b-continuous if it
admits a b-coloring with t colors, for every t = \chi(G),\ldots,\chi_b(G), and
b-monotonic if \chi_b(H_1) \geq \chi_b(H_2) for every induced subgraph H_1 of
G, and every induced subgraph H_2 of H_1.
We investigate the b-chromatic number of graphs with stability number two.
These are exactly the complements of triangle-free graphs, thus including all
complements of bipartite graphs. The main results of this work are the
following:
- We characterize the b-colorings of a graph with stability number two in
terms of matchings with no augmenting paths of length one or three. We derive
that graphs with stability number two are b-continuous and b-monotonic.
- We prove that it is NP-complete to decide whether the b-chromatic number of
co-bipartite graph is at most a given threshold.
- We describe a polynomial time dynamic programming algorithm to compute the
b-chromatic number of co-trees.
- Extending several previous results, we show that there is a polynomial time
dynamic programming algorithm for computing the b-chromatic number of
tree-cographs. Moreover, we show that tree-cographs are b-continuous and
b-monotonic
REDD+ on the rocks? Conflict over forest and politics of justice in Vietnam
Get PDFIn Vietnam, villagers involved in a REDD+ (reduced emissions from deforestation and forest degradation) pilot protect areas with rocks which have barely a tree on them. The apparent paradox indicates how actual practices differ from general ideas about REDD+ due to ongoing conflict over forest, and how contestations over the meaning of justice are a core element in negotiations over REDD+. We explore these politics of justice by examining how the actors involved in the REDD+ pilot negotiate the particular subjects, dimensions, and authority of justice considered relevant, and show how politics of justice are implicit to practical decisions in project implementation. Contestations over the meaning of justice are an important element in the practices and processes constituting REDD+ at global, national and local levels, challenging uniform definitions of forest justice and how forests ought to be managed
Rumours, sects and rallies : the ethnic politics of recent Hmong Millenarian movements in Vietnam’s highlands
Get PDFContrary to modernist assumptions, millenarianism has not died out but continues to influence the politics of many marginalised groups in upland Southeast Asia, including the Hmong. This article summarises and analyses post-World War II Hmong millenarian activity in Vietnam, focusing on three case studies from the 1980s onwards, within the political backdrop of ongoing government suspicions of ethnic separatism and foreign interference. Far from being isolated or peripheral, Hmong millenarian rumours and movements interact with overseas diasporas, human rights agencies and international religious networks to influence state responses, sometimes in unexpected ways
Latent domain models for statistical machine translation
Get PDFA data-driven approach to model translation suffers from the data mismatch problem and demands domain adaptation techniques. Given parallel training data originating from a specific domain, training an MT system on the data would result in a rather suboptimal translation for other domains. But does suboptimality of translation happen only in such an extreme scenario of domain mismatch? This dissertation shows that training SMT systems on heterogeneous corpora (e.g. EuroParl) may also result in suboptimal performance of statistical translation systems. Specifically, it is clear that a word/phrase could be translated in different ways when it comes to different domains. The translation statistics induced from word alignment models and phrase-based models, however, reflect translation preferences aggregated over diverse domains in heterogeneous corpora. In this sense, they can be considered as coarse and domain-confused statistics. This dissertation shows that domain-confused statistics may harm performance of both word alignment and phrase-based models. Another important contribution of this dissertation is to provide a principled way to address the problem. We focus on learning the translation statistics with respect to each of diverse domains (i.e. domain-focused translation statistics). With our method of domain induction for translation, we present a comprehensive study of domain adaptation for statistical machine translation, including four specific case studies Data Selection, Phrase-Based Translation, Word Alignment and Rewarding Domain Invariance in translation. Finally, we briefly describe Scorpio, the ILLC-UvA Adaptation System submitted to an adaptation task at WMT 2016, which participated with the language pair of English-Dutch. This system consolidates the ideas in the thesis on latent variable models for adaptation. Results validate the effective adaptation performance in a competitive setting
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