280 research outputs found

    Linearly scaling direct method for accurately inverting sparse banded matrices

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    In many problems in Computational Physics and Chemistry, one finds a special kind of sparse matrices, termed "banded matrices". These matrices, which are defined as having non-zero entries only within a given distance from the main diagonal, need often to be inverted in order to solve the associated linear system of equations. In this work, we introduce a new O(n) algorithm for solving such a system, being n X n the size of the matrix. We produce the analytical recursive expressions that allow to directly obtain the solution, as well as the pseudocode for its computer implementation. Moreover, we review the different options for possibly parallelizing the method, we describe the extension to deal with matrices that are banded plus a small number of non-zero entries outside the band, and we use the same ideas to produce a method for obtaining the full inverse matrix. Finally, we show that the New Algorithm is competitive, both in accuracy and in numerical efficiency, when compared to a standard method based in Gaussian elimination. We do this using sets of large random banded matrices, as well as the ones that appear when one tries to solve the 1D Poisson equation by finite differences.Comment: 24 pages, 5 figures, submitted to J. Comp. Phy

    GiViP: A Visual Profiler for Distributed Graph Processing Systems

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    Analyzing large-scale graphs provides valuable insights in different application scenarios. While many graph processing systems working on top of distributed infrastructures have been proposed to deal with big graphs, the tasks of profiling and debugging their massive computations remain time consuming and error-prone. This paper presents GiViP, a visual profiler for distributed graph processing systems based on a Pregel-like computation model. GiViP captures the huge amount of messages exchanged throughout a computation and provides an interactive user interface for the visual analysis of the collected data. We show how to take advantage of GiViP to detect anomalies related to the computation and to the infrastructure, such as slow computing units and anomalous message patterns.Comment: Appears in the Proceedings of the 25th International Symposium on Graph Drawing and Network Visualization (GD 2017

    Europeanisation should meet international constructivism: the Nordic Plus group and the internalisation of political conditionality by France and the United Kingdom

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    This article is a plausibility probe for the significance of international constructivist ‘mediating factors’ to explain variation in Europeanisation outcomes. It applies a most similar systems design (or Mill's method of difference) to show that the UK has internalised political conditionality to a larger extent than France at least partially because it has been the object of stronger socialisation pressures within the ‘Nordic Plus’ group. The article contributes to the literature on Europeanisation and development cooperation in two important ways. First, it enlarges its scope of analysis, both geographically (beyond new European Union member states) and thematically (beyond simple measures of aid quality and/or quantity). Second, it emphasises the importance of international (versus domestic) mediating factors. The empirical analysis focusses on three cases of aid sanctions in response to human rights abuses and democratic setbacks: Zimbabwe 2002, Madagascar 2009 and Mozambique 2009

    International Business Cycle Spillovers

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    We apply Diebold-Yilmaz spillover index methodology to monthly industrial production indices to study business cycle interdependence among G-6 industrialized countries since 1958. The business cycle spillover index fluctuates substantially over time, increasing especially after the 1973-75, 1981-82 and 2001 U.S. recessions. The band within which the spillover index fluctuates has widened since the start of the globalization process in the early 1990s. Our most important result, however, concerns the current state of the world economy: In a matter of four months from September to December 2008, the business cycle spillover index recorded the sharpest increase ever, reaching a record level as of December 2008 (See http://data.economicresearchforum.org/erf/bcspill.aspx?lang=en for updates of the spillover plot). Focusing on directional spillover measures, we show that in the current episode the shocks are mostly originating from the United States and spreading to other industrialized countries. We also show that, throughout the period of analysis, the U.S. (1980s and 2000s) and Japan (1970s and 2000s) have been the major transmitters of shocks among the industrialized countries

    Infinite-Variance, Alpha-Stable Shocks in Monetary SVAR: Final Working Paper Version

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    This paper adumbrates a theory of what might be going wrong in the monetary SVAR literature and provides supporting empirical evidence. The theory is that macroeconomists may be attempting to identify structural forms that do not exist, given the true distribution of the innovations in the reduced-form VAR. The paper shows that this problem occurs whenever (1) some innovation in the VAR has an infinite-variance distribution and (2) the matrix ofcoefficients on the contemporaneous terms in the VAR's structural form is nonsingular. Since (2) is almost always required for SVAR analysis, it is germane to test hypothesis (1). Hence, in this paper, we fit a-stable distributions to VAR residuals and, using a parametric-bootstrap method, test the hypotheses that each of the error terms has finite variance

    The Effect of Medicare Eligibility on Spousal Insurance Coverage

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    A majority of married couples in the United States take advantage of the fact that employers often provide health insurance coverage to spouses. When the older spouses become eligible for Medicare, however, many of them can no longer provide their younger spouses with coverage. In this paper, we study how spousal eligibility for Medicare affects the health insurance and health care access of the younger spouse. We find spousal eligibility for Medicare results in the younger spouse having worse insurance coverage and reduced access to health care services
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