Linear Programming Relaxations of Quadratically Constrained Quadratic Programs

We investigate the use of linear programming tools for solving semidefinite programming relaxations of quadratically constrained quadratic problems. Classes of valid linear inequalities are presented, including sparse PSD cuts, and principal minors PSD cuts. Computational results based on instances from the literature are presented.Comment: Published in IMA Volumes in Mathematics and its Applications, 2012, Volume 15

A local branching heuristic for MINLPs

Local branching is an improvement heuristic, developed within the context of branch-and-bound algorithms for MILPs, which has proved to be very effective in practice. For the binary case, it is based on defining a neighbourhood of the current incumbent solution by allowing only a few binary variables to flip their value, through the addition of a local branching constraint. The neighbourhood is then explored with a branch-and-bound solver. We propose a local branching scheme for (nonconvex) MINLPs which is based on iteratively solving MILPs and NLPs. Preliminary computational experiments show that this approach is able to improve the incumbent solution on the majority of the test instances, requiring only a short CPU time. Moreover, we provide algorithmic ideas for a primal heuristic whose purpose is to find a first feasible solution, based on the same scheme

"Sharing" tourism as an opportunity for territorial regeneration: the case of Iseo Lake, Italy

The spread of sharing economics platforms in the world of travels has highlighted the little known phenomenon of the rental of houses and apartments with a non-enterprise management. These accommodations in Italy do not require any guest registration or start-up notification, but the use of websites such as Airbnb has led to a heated debate among the actors operating in the travel and tourism industry. In fact, the regulatory vacuum and the easy-to-use websites would help circumvent the rules in order to “hide away” some business activities. Based on these assumptions, this paper analyses the case of Iseo Lake in the Northern Italy, pointing out the discussions about this new trend in travels and involving not only economic and legal aspects, but also social issues that cannot be ignored. The paper presents “sharing tourism” as an opportunity for territorial regenera-tion in destinations characterized by the presence of few hotel facilities, but also of many empty apartments

Reseña

L. Bosch ; I.L. Llop ; F. Güell Bou ; R. Fusté Suñé ; J. Gimeno ; J.A. Climent i Rovira, I. Torra Sans, "Tarongeta" vol dir taronja petita. Barcelona, Godall Formacions, 2013."Tarongeta" vol dir taronja petita, publicado por Godall Editorial en 2013, incluye seis textos finalistas del concurso "El català pel món". Los autores son jóvenes profesores catalanes, todos nacidos entre la década de los setenta y la de los ochenta, algunos también son investigadores, escritores, poetas, que han vivido la experiencia de enseñar su lengua en los más diversos lugares del mundo."Tarongeta" vol dir taronja petita, publicat per Godall Editorial el 2013, inclou sis textos finalistes del concurs "El català pel món". Els autors són joves professors catalans, tots nascuts entre la dècada dels setanta i la dels vuitanta, alguns també són investigadors, escriptors, poetes, que han viscut l'experiència d'ensenyar la seva llengua en els més diversos llocs del món."Tarongeta" vol dir taronja petita ['Orangete' means little orange] published by Goodall Publishing in 2013 includes the six award-winning texts submitted to the prize ""El català pel món" (Catalan around the world). The authors are young Catalan teachers, all born between the decades of the seventies and eighties. Some of them are also researchers, writers, and poets who describe their experiences of teaching their language in some of the most diverse places in the world

“Tarongeta” vol dir taronja petita por Bosch, L., Llop, I.L., Güell Bou, F., Fusté Suñé, R., Gimeno, J., Climent i Rovira, J.A., & Torra Sans, I. Barcelona, Godall Formacions, 2013.

"Tarongeta" vol dir taronja petita, publicat per Godall Editorial el 2013, inclou sis textos finalistes del concurs "El català pel món". Els autors són joves professors catalans, tots nascuts entre la dècada dels setanta i la dels vuitanta, alguns també són investigadors, escriptors, poetes, que han viscut l'experiència d'ensenyar la seva llengua en els més diversos llocs del món."Tarongeta" vol dir taronja petita ['Orangete' means little orange] published by Goodall Publishing in 2013 includes the six award-winning texts submitted to the prize ""El català pel món" (Catalan around the world). The authors are young Catalan teachers, all born between the decades of the seventies and eighties. Some of them are also researchers, writers, and poets who describe their experiences of teaching their language in some of the most diverse places in the world.“Tarongeta” vol dir taronja petita, publicado por Godall Editorial en 2013, incluye seis textos finalistas del concurso “El català pel món”. Los autores son jóvenes profesores catalanes, todos nacidos entre la década de los setenta y la de los ochenta, algunos también son investigadores, escritores, poetas, que han vivido la experiencia de enseñar su lengua en los más diversos lugares del mundo

Buying a house takes more than hard work and willpower – contrary to government belief

Housing is turning the UK into a land of opportunities for overseas investors but failing its own citizens, writes Alice Belotti. Here, she explains why the recent Housing and Planning Act 2016 is not effectively tackling the three main causes of the housing crisis: insufficient supply; incredibly high rents; and affordability for those on lower incomes

Participatory methodologies for a responsible tourism: the Zinave National Park (Mozambique)

The Zinave National Park (Mozambique), included in a system of protected areas known as the Great Limpopo Transfrontier Park, is the experimental area for the application of a particular approach to the involvement of local communities in the conservation effort: the community conservation. In order to achieve this implicative form, as part of a Ph.D. thesis*, a field research aimed at recovering the local knowledge and the traditional values related to the use of resources in the villages located within the protected area was carried out

Convex envelopes of bounded monomials on two-variable cones

We consider an $n$-variate monomial function that is restricted both in value by lower and upper bounds and in domain by two homogeneous linear inequalities. Such functions are building blocks of several problems found in practical applications, and that fall under the class of Mixed Integer Nonlinear Optimization. We show that the upper envelope of the function in the given domain, for $n\ge 2$ is given by a conic inequality. We also present the lower envelope for $n=2$. To assess the applicability of branching rules based on homogeneous linear inequalities, we also derive the volume of the convex hull for $n=2$.Comment: 22 pages, 12 figure

Eigenstructure assignment in vibrating systems through active and passive approaches

The dynamic behaviour of a vibrating system depends on its eigenstructure, which consists of the eigenvalues and the eigenvectors. In fact, eigenvalues define natural frequencies, damping and settling time, while eigenvectors define the spatial distribution of vibrations, i.e. the mode shape, and also affect the sensitivity of eigenvalues with respect to the system parameters. Therefore, eigenstructure assignment, which is aimed at modifying the system in such a way that it features the desired set of eigenvalues and eigenvectors, is of fundamental importance in mechanical design. However, similarly to several other inverse problems, eigenstructure assignment is inherently challenging, due to its ill-posed nature. Despite the recent advancements of the state of the art in eigenstructure assignment, in fact, there are still important open issues. The available methods for eigenstructure assignment can be grouped into two classes: passive approaches, which consist in modifying the physical parameters of the system, and active approaches, which consist in employing actuators and sensors to exert suitable control forces as determined by a specified control law. Since both these approaches have advantages and drawbacks, it is important to choose the most appropriate strategy for the application of interest. In the present thesis, in fact, are collected passive, active, and even hybrid methods, in which active and passive techniques are concurrently employed. All the methods proposed in the thesis are aimed at solving open issues that emerged from the literature and which have applicative relevance, as well as theoretical. In contrast to several state-of-the-art methods, in fact, the proposed ones implement strategies that enable to ensure that the computed solutions are meaningful and feasible. Moreover, given that in modern mechanical design large-scale systems are increasingly common, computational issues have become a major concern and thus have been adequately addressed in the thesis. The proposed methods have been developed to be general and broadly applicable. In order to demonstrate the versatility of the methods, in the thesis it is provided an extensive numerical assessment, hence diverse test-cases have been used for validation purposes. In order to evaluate without bias the performances of the proposed methods, it has been chosen to employ well-established benchmarks from the literature. Moreover, selected experimental applications are presented in the thesis, in order to determine the capabilities of the developed methods when critically challenged. Given the focus on these issues, it is expected that the methods here proposed can constitute effective tools to improve the dynamic behaviour of vibrating systems and it is hoped that the present work could contribute to spread the use of eigenstructure assignment in the solution of engineering design problems