Linear Time Feature Selection for Regularized Least-Squares

We propose a novel algorithm for greedy forward feature selection for regularized least-squares (RLS) regression and classification, also known as the least-squares support vector machine or ridge regression. The algorithm, which we call greedy RLS, starts from the empty feature set, and on each iteration adds the feature whose addition provides the best leave-one-out cross-validation performance. Our method is considerably faster than the previously proposed ones, since its time complexity is linear in the number of training examples, the number of features in the original data set, and the desired size of the set of selected features. Therefore, as a side effect we obtain a new training algorithm for learning sparse linear RLS predictors which can be used for large scale learning. This speed is possible due to matrix calculus based short-cuts for leave-one-out and feature addition. We experimentally demonstrate the scalability of our algorithm and its ability to find good quality feature sets.Comment: 17 pages, 15 figure

The general circulation of the atmosphere

Theories of how Earth's surface climate may change in the future, of how it may have been in the past, and of how it is related to climates of other planets must build upon a theory of the general circulation of the atmosphere. The view of the atmospheric general circulation presented here focuses not on Earth's general circulation as such but on a continuum of idealized circulations with axisymmetric flow statistics. Analyses of observational data for Earth's atmosphere, simulations with idealized general circulation models, and theoretical considerations suggest how characteristics of the tropical Hadley circulation, of the extratropical circulation, and of atmospheric macroturbulence may depend on parameters such as the planet radius and rotation rate and the strength of the differential heating at the surface

Vortex Mass in a Superfluid

We consider the inertial mass of a vortex in a superfluid. We obtain a vortex mass that is well defined and is determined microscopically and self-consistently by the elementary excitation energy of the kelvon quasiparticle localised within the vortex core. The obtained result for the vortex mass is found to be consistent with experimental observations on superfluid quantum gases and vortex rings in water. We propose a method to measure the inertial rest mass and Berry phase of a vortex in superfluid Bose and Fermi gases.Comment: 12 pages, 1 figur

Capital Accumulation and Employment Cycles in a Model of Creative Destruction

A Schumpeterian growth model is constructed for an economy with wage bargaining. It is shown that the economy is subject to cycles in which capital, output and employment vary in fixed proportion. These increase through saving and capital accumulation until a new technology is introduced, at which moment they fall sharply due to obsolescence of capital. When the labour market is deregulated to weaken workers' position in bargaining, the labour-capital ratio increases but the average growth rate of the economy decreases. The growth cycle can be socially optimal. An elasticity rule is given for when the labour market should be regulated and when deregulated

Competition, Imitation and Growth with Non-Diversifiable Risk

This paper analyzes the growth and welfare effects of competition in an endogenously-growing economy with imitation and non-diversifiable risk. The main findings are as follows. There is no imitation without positive profits during innovation races. A larger proportion of competing industries leads to slower economic growth. When competitive profits are high or low, the economy grows faster than when they are of medium size. If the government subsidizes innovation and imitation optimally, then competitive profits are positively associated with welfare. With an optimal uniform subsidy to all R&D, there is an “inverted-U” relationship between competitive profits and welfare.Imitation, competition, Schumpeterian growth

Effects of fiscal policy on the durability of low inflation regimes

This paper deals with the interaction of fiscal and monetary policy when the central bank is pursuing a price stability-oriented monetary policy. In particular, we study the durability of the price stability regime when public debt accumulates as a result of ultimately unsustainable deficits. The growth of indebtedness causes the collapse of the price stability regime after a period of rising deficits. The budget deficit is endogenously determined in the model, as a result of government’s decisions on how to finance its expenditure. The alternative methods of finance are taxes, debt, and seigniorage. Under the price stability regime, only the first two methods are available, but in the long run taxes and seigniorage are the only alternatives. The price stability regime collapses when the public debt reaches an edogenously determined threshold, which makes reneging on price stability as attractive as accumulating more tax burden for the future. We are able to solve for the critical level of debt, the timing of the collapse, and the reaction of taxes to the collapse of the price stability regime. The critical level of debt depends, inter alia, on the level of government consumption, the real interest rate, the velocity of money, and the efficiency-effects of taxation. The results are illustrated by several numerical simulations.inflation; fiscal policy; fiscal theory of inflation; Stability and Growth Pact