12,127 research outputs found
Strongly Vertex-Reinforced-Random-Walk on the complete graph
We study Vertex-Reinforced-Random-Walk on the complete graph with weights of
the form , with . Unlike for the
Edge-Reinforced-Random-Walk, which in this case localizes a.s. on 2 sites, here
we observe various phase transitions, and in particular localization on
arbitrary large sets is possible, provided is close enough to 1. Our
proof relies on stochastic approximation techniques. At the end of the paper,
we also prove a general result ensuring that any strongly reinforced VRRW on
any bounded degree graph localizes a.s. on a finite subgraph.Comment: 19 p
Global versus Country-Specific Shocks and International Business Cycles
This paper documents the relative importance of global and country-specific shocks for international business cycles. For this purpose, we rely on a symmetric two-country, dynamic, general-equilibrium model with costly, incomplete, international financial markets. We also relate exogenous technologies and government expenditures to unobservable common and idiosynchratic components, and apply a Kalman filter to extract the associated global and country-specific shocks. We show that the baseline parametrization of the model, including all shocks, closely matches the cyclical fluctuations of key macroeconomic variables for the United States and a non-US aggregate over the post-1975 period. We then experiment alternative parametrizations, isolating the effects of each shock, and find that country-specific technology shocks constitute a prime determinant of international business cycles. Also, global technology shocks have marginal contributions, whereas global and country-specific government-expenditure shocks have negligible effects on cyclical fluctuations.General Equilibrium, Kalman Filter, Symmetric Economies
Efficient dielectric matrix calculations using the Lanczos algorithm for fast many-body implementations
We present a implementation that assesses the two major bottlenecks
of traditional plane-waves implementations, the summations over conduction
states and the inversion of the dielectric matrix, without introducing new
approximations in the formalism. The first bottleneck is circumvented by
converting the summations into Sternheimer equations. Then, the novel avenue of
expressing the dielectric matrix in a Lanczos basis is developed, which reduces
the matrix size by orders of magnitude while being computationally efficient.
We also develop a model dielectric operator that allows us to further reduce
the size of the dielectric matrix without accuracy loss. Furthermore, we
develop a scheme that reduces the numerical cost of the contour deformation
technique to the level of the lightest plasmon pole model. Finally, the use of
the simplified quasi-minimal residual scheme in replacement of the conjugate
gradients algorithm allows a direct evaluation of the corrections at
the desired real frequencies, without need for analytical continuation. The
performance of the resulting implementation is demonstrated by
comparison with a traditional plane-waves implementation, which reveals a
500-fold speedup for the silane molecule. Finally, the accuracy of our
implementation is demonstrated by comparison with other calculations
and experimental results.Comment: 19 pages, 2 figure
Global versus Country-Specific Shocks and International Business Cycles
This paper documents the relative importance of global and country-specific shocks for international business cycles. For this purpose, we rely on a symmetric two-country, dynamic, general-equilibrium model with costly, incomplete, international financial markets. We also relate exogenous technologies and government expenditures to unobservable common and idiosynchratic components, and apply a Kalman filter to extract the associated global and country-specific shocks. We show that the baseline parametrization of the model, including all shocks, closely matches the cyclical fluctuations of key macroeconomic variables for the United States and a non-US aggregate over the post-1975 period. We then experiment alternative parametrizations, isolating the effects of each shock, and find that country-specific technology shocks constitute a prime determinant of international business cycles. Also, global technology shocks have marginal contributions, whereas global and country-specific government-expenditure shocks have negligible effects on cyclical fluctuations.General Equilibrium, Kalman Filter, Symmetric Economies.
A world without farmers? Food production, inclusive development and ecology: Historical Evidences for a New Deal
This paper questions the perspective of a "world without agriculture" which underpins the economic paradigm of "structural transformation" and "modern growth". It does so by recomposing worldwide land and labour productivity trends in caloric terms from 1961 to 2007 and by providing an heuristic model showing that the "Lewis Path" to prosperity is only one out of four possible pathways. It shows that more than half of the world population is rather embarked in a "Lewis Trap" where farmers are increasingly numerous and relatively poorer. It highlights how land scarcity and insufficient job opportunities outside agriculture prevent them to increase their labour productivity and incomes with motorized machineries. The emerging paradigm of "ecological intensification" might contribute to overcome the current deadlocks by redirecting worldwide R&D towards small-scale knowledge-intensive and context-specific agricultures overlapping the manufacture and service sectors. (Résumé d'auteur
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