Laurent Simon

Minimum satisfiability and its applications

We define solving techniques for the Minimum Satisfiability Problem (MinSAT), propose an efficient branch-and-bound algorithm to solve the Weighted Partial MinSAT problem, and report on an empirical evaluation of the algorithm on Min-3SAT, Max-Clique, and combinatorial auction problems. Techniques solving MinSAT are substantially different from those for the Maximum Satisfiability Problem (MaxSAT). Our results provide empirical evidence that solving combinatorial optimization problems by reducing them to MinSAT may be substantially faster than reducing them to MaxSAT, and even competitive with specific algorithms. We also use MinSAT to study an interesting correlation between the minimum number and the maximum number of satisfied clauses of a SAT instance.

Virtual Garden Computer Program for use in Exploring the Elements of Biodiversity People Want in Cities

Urban ecology is emerging as an integrative science that explores the interactions of people and biodiversity in cities. Interdisciplinary research requires the creation of new tools that allow the investigation of relations between people and biodiversity. It has been established that access to green spaces or nature benefits city dwellers, but the role of species diversity in providing psychological benefits remains poorly studied. We developed a user-friendly 3-dimensional computer program (Virtual Garden [www.tinyurl.com/3DVirtualGarden]) that allows people to design their own public or private green spaces with 95 biotic and abiotic features. Virtual Garden allows researchers to explore what elements of biodiversity people would like to have in their nearby green spaces while accounting for other functions that people value in urban green spaces. In 2011, 732 participants used our Virtual Garden program to design their ideal small public garden. On average gardens contained 5 different animals, 8 flowers, and 5 woody plant species. Although the mathematical distribution of flower and woody plant richness (i.e., number of species per garden) appeared to be similar to what would be expected by random selection of features, 30% of participants did not place any animal species in their gardens. Among those who placed animals in their gardens, 94% selected colorful species (e.g., ladybug [Coccinella septempunctata], Great Tit [Parus major], and goldfish), 53% selected herptiles or large mammals, and 67% selected non-native species. Older participants with a higher level of education and participants with a greater concern for nature designed gardens with relatively higher species richness and more native species. If cities are to be planned for the mutual benefit of people and biodiversity and to provide people meaningful experiences with urban nature, it is important to investigate peoples relations with biodiversity further. Virtual Garden offers a standardized tool with which to explore these relations in different environments, cultures, and countries. It can also be used by stakeholders (e.g., city planners) to consider peoples opinions of local design.

Biodiversité : les services écosystémiques et la nature en ville

Unfortunately, it is common to oppose nature and cities. This oversimplification gets in the way of acquiring nknowledge about the conditions necessary for the conservation of biodiversity in anthropic environments. The nobjective of this paper is to go beyond the crude opposition between city and nature and highlight the ncomplexity of the relationships that urban environments have with nature. We first show that cities and nnature form two closely intertwined systems and have done so ever since cities came into being. We go on nto distinguish two different ways of looking at nature in cities: the perspective that sees nature objects as npart of the street furniture and another that sees nature from the angle of biodiversity. By way of conclusion, nwe discuss three important issues relating to the management of that biodiversity.