A Comparison of some recent Task-based Parallel Programming Models

The need for parallel programming models that are simple to use and at the same time efficient for current ant future parallel platforms has led to recent attention to task-based models such as Cilk++, Intel TBB and the task concept in OpenMP version 3.0. The choice of model and implementation can have a major impact on the final performance and in order to understand some of the trade-offs we have made a quantitative study comparing four implementations of OpenMP (gcc, Intel icc, Sun studio and the research compiler Mercurium/nanos mcc), Cilk++ and Wool, a high-performance task-based library developed at SICS. Abstract. We use microbenchmarks to characterize costs for task-creation and stealing and the Barcelona OpenMP Tasks Suite for characterizing application performance. By far Wool and Cilk++ have the lowest overhead in both spawning and stealing tasks. This is reflected in application performance when many tasks with small granularity are spawned where Cilk++ and, in particular, has the highest performance. For coarse granularity applications, the OpenMP implementations have quite similar performance as the more light-weight Cilk++ and Wool except for one application where mcc is superior thanks to a superior task scheduler. Abstract. The OpenMP implemenations are generally not yet ready for use when the task granularity becomes very small. There is no inherent reason for this, so we expect future implementations of OpenMP to focus on this issue

Models of kleptoparasitism on networks: the effect of population structure on food stealing behaviour

The behaviour of populations consisting of animals that interact with each other for their survival and reproduction is usually investigated assuming homogeneity amongst the animals. However, real populations are non-homogeneous. We focus on an established model of kleptoparasitism and investigate whether and how much population heterogeneities can affect the behaviour of kleptoparasitic populations. We consider a situation where animals can either discover food items by themselves or attempt to steal the food already discovered by other animals through aggressive interactions. Representing the likely interactions between animals by a network, we develop pairwise and individual-based models to describe heterogeneities in both the population structure and other individual characteristics, including searching and fighting abilities. For each of the models developed we derive analytic solutions at the steady state. The high accuracy of the solutions is shown in various examples of populations with different degrees of heterogeneity. We observe that highly heterogeneous structures can significantly affect the food intake rate and therefore the fitness of animals. In particular, the more highly connected animals engage in more conflicts, and have a reduced food consumption rate compared to poorly connected animals. Further, for equivalent average level of connectedness, the average consumption rate of a population with heterogeneous structure can be higher

A Spatially-related Note on Entrepreneurship and Economic Growth

A large and still growing body of literature suggests that entrepreneurship is of exceptional importance in explaining knowledge spillovers. Although quantifying the impact of entrepreneurial activity for economic growth is an interesting issue – particularly at the regional level – a concise formulation within a theoretical growth model is still missing. This paper in general tries to uncover the link between own- and neighbour-related regional entrepreneurial activity in innovation and regional growth within a spatial semi-endogenous growth model in the spirit of Jones (1995) reflecting recent empirical findings on entrepreneurial activity for economic growth. The paper derives an explicit solution for the transitional as well as for the balanced growth path level of ideas.entrepreneurship, economic growth, innovation, knowledge spillover

The Flexible Substitution Logit: Uncovering Category Expansion and Share Impacts of Marketing Instruments

Different instruments are relevant for different marketing objectives (category demand expansion or market share stealing). To help brand managers make informed marketing mix decisions, it is essential that marketing mix models appropriately measure the different effects of marketing instruments. Discrete choice models that have been applied to this problem might not be adequate because they possess the Invariant Proportion of Substitution (IPS) property, which imposes counter-intuitive restrictions on individual choice behavior. Indeed our empirical application to prescription writing choices of physicians in the hyperlipidemia category shows this to be the case. We find that three commonly used models that all suffer from the IPS restriction - the homogeneous logit model, the nested logit model, and the random coefficient logit model - lead to counter-intuitive estimates of the sources of demand gains due to increased marketing investments in Direct-to-Consumer Advertising (DTCA), detailing, and Meetings and Events (M&E). We then propose an alternative choice model specification that relaxes the IPS property - the so-called "flexible substitution" logit (FSL) model. The (random coefficient) FSL model predicts that sales gains from DTCA and M&E come primarily from the non-drug treatment (87.4% and 70.2% respectively), whereas gains from detailing come at the expense of competing drugs (84%). By contrast, the random coefficient logit model predicts that gains from DTCA, M&E and detailing all would come largely from competing drugs.

Asymmetry and Discrimination in Internet Peering Evidence from the LINX

Is the quality of interconnection between Internet operators affected by their asymmetry? While recent game theoretic literature provides contrasting answers to this question, there is a lack of empirical research. We introduce a novel dataset based on Internet routing policies, and study the interconnection decisions amongst the Internet Service Providers (ISPs) members of the London Internet Exchange Point (LINX). Our results show that interconnection quality degradation can be significantly explained by asymmetry between providers. We also show that Competition Authorities should focus more on the role played by the “centrality of an operatorâ€, rather than on its market share.Internet Peering, Two-sided Markets, Network Industries, Antitrust, Net Neutrality