A Fast Active Set Block Coordinate Descent Algorithm for ℓ1\ell_1-regularized least squares

The problem of finding sparse solutions to underdetermined systems of linear equations arises in several applications (e.g. signal and image processing, compressive sensing, statistical inference). A standard tool for dealing with sparse recovery is the $\ell_1$-regularized least-squares approach that has been recently attracting the attention of many researchers. In this paper, we describe an active set estimate (i.e. an estimate of the indices of the zero variables in the optimal solution) for the considered problem that tries to quickly identify as many active variables as possible at a given point, while guaranteeing that some approximate optimality conditions are satisfied. A relevant feature of the estimate is that it gives a significant reduction of the objective function when setting to zero all those variables estimated active. This enables to easily embed it into a given globally converging algorithmic framework. In particular, we include our estimate into a block coordinate descent algorithm for $\ell_1$-regularized least squares, analyze the convergence properties of this new active set method, and prove that its basic version converges with linear rate. Finally, we report some numerical results showing the effectiveness of the approach.Comment: 28 pages, 5 figure

Principle of Subsidiarity and "Embeddedness" of the European Convention on Human Rights in the field of the Reasonable Time Requirement: The Italian Case

The right to ‘domestic remedies’, which ideally connects ‘subsidiarity’ and ‘embeddedness’ of the ECHR in the legal systems of member States, is deemed to play a crucial role for the Strasbourg machinery survival as well as for an effective protection of human rights, especially in the field of the ‘reasonable-time’ requirement. In this respect the Italian case seems an excellent test. Once a compensatory remedy was introduced in the Italian legal system by Law No. 89 of 2001 (the ‘Pinto Act’), it soon appeared that such a remedy could be considered ‘effective’ in so far as it was implemented in accordance with the ECtHR’s jurisprudence. Therefore a legal tool for the interaction between ECtHR and Italian courts had to be found. Nevertheless, the results of this interaction might suggest that the domestic remedy has neither increased the protection of the reasonable-time requirement in Italy nor is it the final solution to the ECtHR’s overloa

Il divieto di tortura e gli obblighi degli Stati membri nella giurisprudenza della Corte EDU

La comunicazione ha avuto ad oggetto il divieto di tortura ai sensi dell'art. 3 CED

The RSB order parameter in finite-dimensional spin glasses: numerical computation at zero temperature

This thesis is focused on the computation of the overlap distribution which characterizes spin glasses with finite connectivity upon an RSB transition at zero temperature. Two models are considered: the J± Bethe lattice spin glass and the Edwards-Anderson spin glass in three dimensions with random regular bond dilution (random dilution with the constraint of fixed connectivity z = 3). The approach is based on the study of the effects of a bulk perturbation on the energy landscape. In ultrametric spin glasses, the distribution of the excited states is known to be related to the order parameter through a universal formula. This formula is used for deriving the order parameter from the experimental distributions. In addition, the finite-size corrections to the ground state energy are computed for the two models

Direct Selling: a Marketing Strategy to Shorten Distances between Production and Consumption

Direct sales became in recent years a diversification strategy increasingly used by farms to answer the CAP reform, as well as to react to the continuous price squeeze. Direct sales is in fact a form of marketing that allow farmers to retain a higher share of the final value of products. Far from being a way back to tradition, short chains and direct sales can be seen as strategies to capture new segments of demand interested in local and fresh food, and in more direct contact between consumers and suppliers. The aim of this work is to study the recent evolution of direct selling in Italy and the determinants of the adoption of this marketing strategy. The first part of the paper analyses the evolution of Italian short supply chains and the development of the related institutional framework (national laws and financial incentives). In the second part of the paper the analysis is focused on the determinants of the adoption of direct selling. Specific attention will be devoted to empirically test if the probability of using of this marketing channel is influenced by the farm location in proximity to urban areas.farm diversification, direct selling, short supply chain, periurban agriculture, discrete choice models, Marketing,

An Active-Set Algorithmic Framework for Non-Convex Optimization Problems over the Simplex

In this paper, we describe a new active-set algorithmic framework for minimizing a non-convex function over the unit simplex. At each iteration, the method makes use of a rule for identifying active variables (i.e., variables that are zero at a stationary point) and specific directions (that we name active-set gradient related directions) satisfying a new "nonorthogonality" type of condition. We prove global convergence to stationary points when using an Armijo line search in the given framework. We further describe three different examples of active-set gradient related directions that guarantee linear convergence rate (under suitable assumptions). Finally, we report numerical experiments showing the effectiveness of the approach.Comment: 29 pages, 3 figure

Classification of ductile cast iron specimens: A machine learning approach

In this paper an automatic procedure based on a machine learning approach is proposed to classify ductile cast iron specimens according to the American Society for Testing and Materials guidelines. The mechanical properties of a specimen are strongly influenced by the peculiar morphology of their graphite elements and useful characteristics, the features, are extracted from the specimens’ images; these characteristics examine the shape, the distribution and the size of the graphite particle in the specimen, the nodularity and the nodule count. The principal components analysis are used to provide a more efficient representation of these data. Support vector machines are trained to obtain a classification of the data by yielding sequential binary classification steps. Numerical analysis is performed on a significant number of images providing robust results, also in presence of dust, scratches and measurement noise

Right of individual application to the ECtHR: achievements and obstacles

Nella comunicazione si sono messi in evidenza l' "acquis" relativo al diritto di ricorso individuale innanzi alla Corte europea dei diritti dell'uomo (in specie in prospettiva di effettività) e le principali zone d'ombra (formalismo della Corte, elevato numero di declaratorie di irricevibilità ecc.