Carlo Fantozzi

Coupling different methods for overcoming the class imbalance problem

Many classification problems must deal with imbalanced datasets where one class - the majority class - outnumbers the other classes. Standard classification methods do not provide accurate predictions in this setting since classification is generally biased towards the majority class. The minority classes are oftentimes the ones of interest (e.g., when they are associated with pathological conditions in patients), so methods for handling imbalanced datasets are critical.Using several different datasets, this paper evaluates the performance of state-of-the-art classification methods for handling the imbalance problem in both binary and multi-class datasets. Different strategies are considered, including the one-class and dimension reduction approaches, as well as their fusions. Moreover, some ensembles of classifiers are tested, in addition to stand-alone classifiers, to assess the effectiveness of ensembles in the presence of imbalance. Finally, a novel ensemble of ensembles is designed specifically to tackle the problem of class imbalance: the proposed ensemble does not need to be tuned separately for each dataset and outperforms all the other tested approaches.To validate our classifiers we resort to the KEEL-dataset repository, whose data partitions (training/test) are publicly available and have already been used in the open literature: as a consequence, it is possible to report a fair comparison among different approaches in the literature.Our best approach (MATLAB code and datasets not easily accessible elsewhere) will be available at https://www.dei.unipd.it/node/2357.

On the Effectiveness of D-BSP as a Bridging Model of Parallel Computation

This paper surveys and places into perspective a number of results concerning the D-BSP (Decomposable Bulk Synchronous Parallel) model of computation, a variant of the popular BSP model proposed byValiant in the early nineties. D-BSP captures part of the proximity structure of the computing platform, modeling it by suitable decompositions into clusters, each characterized by its own bandwidth and latency parameters. Quantitative evidence is provided that, when modeling realistic parallel architectures, D-BSP achieves higher effectiveness and portability than BSP, without significantly affecting the ease of use. It is also shown that D-BSP avoids some of the shortcomings of BSP which motivated the definition of other variants of the model. Finally, the paper discusses how the aspects of network proximity incorporated in the model allow for a better management of network congestion and bank contention, when supporting a shared-memory abstraction in a distributed-memory environment.

A GENERAL PRAM SIMULATION SCHEME FOR CLUSTERED MACHINES

We present a general deterministic scheme to implement a shared memory abstraction on any distributed-memory machine which exhibits a clustered structure. More specifically, we develop a memory distribution strategy and an access protocol for the Decomposable BSP (D-BSP), a generic machine model whose bandwidth/latency parameters can be instantiated to closely reflect the characteristics of machines that admit a hierarchical decomposition into independent clusters. Our scheme achieves provably optimal slowdown for those machines where delays due to latency dominate over those due to bandwidth limitations. For machines where this is not the case, the slowdown is a mere logarithmic factor away from the natural bandwidth-based lower bound.

Accessing Tape Music Documents on Mobile Devices

The aim of this article is to present and discuss an innovative methodology aimed at accessing digitized copies of historical tape music audio documents; the methodology leverages on the multimedia and multisensory capabilities of mobile devices to provide an unprecedented level of fruition. In addition to the methodology, and stemming from it, we present an actual software application for Android tablet devices. This novel piece of software was designed and developed in a multidisciplinary team involving engineers as well as musicians, composers, and archivists. The strongest element in our work is the fact that it follows a rigorous process and it is based on the principles of philological awareness; thus, it also takes into consideration the critical points in the musicologists domain such as (i) the definition of preservation (i.e., master) copy, (ii) the importance of secondary information, (iii) the history of production and transmission of audio documents.

Implementing shared memory on clustered machines

We present a general deterministic scheme to implement a shared memory abstraction on any distributed-memory machine which exhibits a clustered structure. More specifically, we develop a memory distribution strategy and an access protocol for the Decomposable BSP (D-BSP), a generic machine model whose bandwidth/latency parameters can be instantiated to closely reflect the characteristics of machines that admit a hierarchical decomposition into independent clusters. Our scheme achieves provably optimal slowdown for those machines where delays due to latency dominate over those due to bandwidth limitations. For machines where this is not the case, the slowdown is a mere logarithmic factor away from the natural bandwidth-based lower bound. An important feature of the scheme is that it can be made fully constructive for small memory sizes, while for larger sizes it relies solely on nonconstructive graphs of weak expansion.

Tape music archives: from preservation to access

This article presents a methodology for the active preservation of, and the access to, magnetic tapes of audio archives. The methodology has been defined and implemented by a multidisciplinary team involving engineers as well as musicians, composers and archivists. The strong point of the methodology is the philological awareness that influenced the development of digital tools, which consider the critical questions in the historian and musicologist’s approach: the secondary information and the history of transmission of an audio document.

Seamless Integration of Parallelism and Memory Hierarchy

We prove an analogue of Brents lemma for BSP-like parallel machines featuring a hierarchical structure for both the interconnection and the memory. Specifically, for these machines we present a uniform scheme to simulate any computation designed for v processors on a v?-processor configuration with v? ? v and the same overall memory size. For a wide class of computations the simulation exhibits optimal O (v/v?) slowdown. The simulation strategy aims at translating communication locality into temporal locality. As an important special case (v? = 1), our simulation can be employed to obtain efficient hierarchy-conscious sequential algorithms from efficient fine-grained ones.

How behavior in mobile games relates to psychological indicators

Besides being one of the most popular forms of entertainment among younger generations, video games have been exploited in education for their potential to engage learners. However, a quantitative appraisal of the mechanisms behind their effectiveness is still in progress. This paper investigates the relation between psychological variables and behavior while playing on mobile devices like smartphones and tablets. A mobile implementation of the Connect 4 game (“Addiction 4”) was designed to engage users while collecting data in the background. The app was then given to a group of students, who were also separately administered a battery of psychological tests. By merging the data from tests and gameplay, some noteworthy relations were discovered between indicators of psychological characteristics and metrics derived from the game.

SDR implementation of a DVB-T2 transmitter: The core building blocks

In this paper we describe the implementation of a DVB-T2 transmitter on a commercially-available hardware platform. The implementation leverages on the Software-Defined Radio (SDR) characteristics of the platform to attain on-the fly reconfigurability. The paper focuses on the two most computationally intensive blocks of the transmitter: the LDPC encoder and the IFFT processor.