An Inexact Successive Quadratic Approximation Method for Convex L-1 Regularized Optimization

We study a Newton-like method for the minimization of an objective function that is the sum of a smooth convex function and an l-1 regularization term. This method, which is sometimes referred to in the literature as a proximal Newton method, computes a step by minimizing a piecewise quadratic model of the objective function. In order to make this approach efficient in practice, it is imperative to perform this inner minimization inexactly. In this paper, we give inexactness conditions that guarantee global convergence and that can be used to control the local rate of convergence of the iteration. Our inexactness conditions are based on a semi-smooth function that represents a (continuous) measure of the optimality conditions of the problem, and that embodies the soft-thresholding iteration. We give careful consideration to the algorithm employed for the inner minimization, and report numerical results on two test sets originating in machine learning

A symmetric rank-one Quasi-Newton line-search method using negative curvature directions

We propose a quasi-Newton line-search method that uses negative curvature directions for solving unconstrained optimization problems. In this method, the symmetric rank-one (SR1) rule is used to update the Hessian approximation. The SR1 update rule is known to have a good numerical performance; however, it does not guarantee positive definiteness of the updated matrix. We first discuss the details of the proposed algorithm and then concentrate on its numerical efficiency. Our extensive computational study shows the potential of the proposed method from different angles, such as; its second order convergence behavior, its exceeding performance when compared to two other existing packages, and its computation profile illustrating the possible bottlenecks in the execution time. We then conclude the paper with the convergence analysis of the proposed method

Implementation of a fixing strategy and parallelization in a recent global optimization method

Electromagnetism-like Mechanism (EM) heuristic is a population-based stochastic global optimization method inspired by the attraction-repulsion mechanism of the electromagnetism theory. EM was originally proposed for solving continuous global optimization problems with bound constraints and it has been shown that the algorithm performs quite well compared to some other global optimization methods. In this work, we propose two extensions to improve the performance of the original algorithm: First, we introduce a fixing strategy that provides a mechanism for not being trapped in local minima, and thus, improves the effectiveness of the search. Second, we use the proposed fixing strategy to parallelize the algorithm and utilize a cooperative parallel search on the solution space. We then evaluate the performance of our study under three criteria: the quality of the solutions, the number of function evaluations and the number of local minima obtained. Test problems are generated by an algorithm suggested in the literature that builds test problems with varying degrees of difficulty. Finally, we benchmark our results with that of the Knitro solver with the multistart option set

Zonas militares: Un remedio para despertar a Ankara de la amnesia urbana

[EN] The historical context of Ankara is relatively complex due to the breaking points in its history. First, Ankara became the showcase of the newly established Turkish Republic and a new city center designed in isolation with the old one to represent the modernity of the Republic. Second, with the 1980 coup and expansion of the military zones, the new city center expanded unplanned and unexpected. Last, after the coup attempt in 2016, the large military zones in the city center are decided to be relocated to the city’s peripheries. This study points out the importance of this recent decision on the historical landscape of Ankara and proposes that it could be a potential for repairing the urban memory of the city. According to these massive changes, Ankara lost many of her historical references and the continuity of the urban memory. In this context, this paper thoroughly discusses the remaking of military zones in the city center, their historical presence, and possible interactions with the city’s needs. Understanding these areas as potential catalysts for repairing the historical landscape requires developing a new perspective, which embraces complex relations and multiple voices. Dialogic and polyphonic thinking encompasses the city’s inherent multiplicity, relationality, incompleteness, and historical assets.[CA] El context històric d’Ankara és relativament complex a causa dels punts de ruptura de la seua història. En primer lloc, Ankara es va convertir en l’aparador de la recentment creada República Turca i es va dissenyar un nou centre urbà aïllat de l’antic per a representar la modernitat de la República. En segon lloc, amb el colp d’estat de 1980 i l’expansió de les zones militars, el nou centre de la ciutat es va expandir de manera imprevista i no planificada. Finalment, després de la temptativa colpista de 2016, es decideix reubicar les grans zones militars del centre de la ciutat en les perifèries. Aquest estudi assenyala la importància d’aquesta recent decisió en el paisatge històric d’Ankara i proposa que podria ser un potencial per a reparar la memòria urbana de la ciutat. A causa d’aquests canvis massius, Ankara ha perdut moltes de les seues referències històriques i la continuïtat de la memòria urbana. En aquest context, aquest article analitza a fons la reconstrucció de les zones militars en el centre de la ciutat, la seua presència històrica i les seues possibles interaccions amb les necessitats de la ciutat. Entendre aquestes zones com a potencials catalitzadors de la reparació del paisatge històric requereix desenvolupar una nova perspectiva, que abaste relacions complexes i veus múltiples. El pensament dialògic i polifònic engloba la multiplicitat, la relacionalitat, el caràcter incomplet i els actius històrics inherents a la ciutat.[ES] El contexto histórico de Ankara es relativamente complejo debido a los puntos de ruptura en su historia. En primer lugar, Ankara se convirtió en el escaparate de la entonces recién establecida República Turca y se diseñó un nuevo centro urbano aislado del antiguo para representar la modernidad de la República. En segundo lugar, con el golpe de 1980 y la expansión de las zonas militares, el nuevo centro urbano se expandió de manera descontrolada y repentina. Finalmente, tras el intento de golpe en 2016, se ha decidido reubicar las grandes zonas militares del centro urbano en la periferia de la ciudad. Este estudio señala la importancia de esta reciente decisión en el paisaje histórico de Ankara y propone que podría ser un elemento potencialmente reparador de la memoria urbana de la ciudad. Debido a estos cambios masivos, Ankara perdió la mayoría de sus referencias históricas y la continuidad de su memoria urbana. En este contexto, el presente trabajo debate concienzudamente la reconstrucción de las zonas militares en el centro de la ciudad, su presencia histórica y las posibles interacciones con las necesidades de la ciudad. Entender estas áreas como potenciales catalizadores para reparar el paisaje histórico requiere desarrollar una nueva perspectiva que contempla relaciones complejas y múltiples voces. El pensamiento dialógico y polifónico abarca la multiplicidad, relacionalidad, incompletitud y bienes históricos inherentes a la ciudad.[FR] Le contexte historique d’Ankara est relativement complexe à cause des points de rupture dans son histoire. D’abord, Ankara est devenu jadis l’étalage de la nouvelle République turque, et un nouveau centre urbain isolé de l’ancien a été conçu pour représenter la modernité de la République. Deuxièmement, avec le coup d’état de 1980 et l’expansion des zones militaires, le nouveau centre urbain s’est élargi de façon incontrôlée et soudaine. Finalement, suite à la tentative de coup en 2016, l’on a décidé de reloger les grandes zones militaires du centre urbain à la périphérie de la ville. Cette étude remarque l’importance de cette récente décision dans le paysage historique d’Ankara et propose que cela pourrait être un élément potentiellement réparateur de la mémoire urbaine de la ville. À cause de ces changements massifs, Ankara a perdu la plupart de ses références historiques, ainsi que la continuité de sa mémoire urbaine. Dans ce contexte-là, ce travail-ci met en débat consciencieusement la reconstruction des zones militaires dans le centre de la ville, sa présence historique et leurs possibles interactions avec les besoins de la ville. Considérer ces zones comme de potentiels catalyseurs pour la réparation du paysage historique exige le développement d’une nouvelle perspective ayant des rapports complexes et des voix multiples. La pensée dialogique et polyphonique couvre la multiplicité, la relationnalité, l’incomplétude et les biens historiques inhérents à la ville.Oztoprak, Z.; Çağlar, N. (2021). Zones militars: Un remei per a despertar a Ankara de l’amnèsia urbana. ANUARI d’Arquitectura i Societat. 0(1):332-351. https://doi.org/10.4995/anuari.2021.16226OJS33235101Bakhtin, Mikhail. "Toward a Methodology for the Human Sciences." En Speech, Genres, and Other Late Essays. Ed. Caryl Emerson i Michael Holquist. Austin: University of Texas, 1986.Bakhtin, Mikhail. The Dialogic Imagination: Four Essays. Ed. M. Holquist. Austin, TX: University of Texas Press, 1981.Bakhtin, Mikhail. Problems of Dostoevsky's poetics. Minneapolis, MN: University of Minnesota Press, 1984.Bakhtin, Mikhail. Rabelais and His World. Bloomington, IN: Indiana University Press, 1984.Boyer, Christine. The City of Collective Memory: Its Historical Imagery and Architectural Entertainments. Cambridge, MA: MIT Press, 1996.Crinson, Mark. Urban Memory: History and Amnesia in the Modern City. New York, NY: Routledge, 2005. https://doi.org/10.4324/9780203414613Folch-Serra, Mireya. "Place, Voice, Space: Mikhail Bakhtin's Dialogical Landscape." Environment and Planning D: Society and Space 8, (1990). https://doi.org/10.1068/d080255Jansen, Hermann. Ankara İmar Planı. İstanbul: Alaeddin Kıral Basımevi, 1937.Kenniff, Thomas Bernard. "A Dialogical Investigation into the Architectonics of Designing Public Space at Barking Town Square." Tesi Doctoral, Bartlett School of Architecture, 2013.Lachmann Renate, Eshelman Raoul, i Davis Marc. "Bakhtin and Carnival: Culture as Counter-Culture." Cultural Critique, no. 11 (1988). https://doi.org/10.2307/1354246Sennett, Richard. Together: The Rituals, Pleasures, and Politics of Cooperation. New Haven, CT, USA: Yale University Press, 2012.Şahin, Savaş Zafer. "Can Military Zones be an Opportunity for Revitalizing Ankara's Green Belt and Upper Scale Urban Planning?." Planlama, 26 (3) (2016). https://doi.org/10.14744/planlama.2016.74745Todorov, Tzvetan. Mikhail Bakhtin: The Dialogical Principle, Theory and History of Literature. Manchester: Manchester University Press, 1984

Research capacity and training needs for non-communicable diseases in the public health arena in Turkey

Background The aim of this study is to define the research capacity and training needs for professionals working on non-communicable diseases (NCDs) in the public health arena in Turkey. Methods This study was part of a comparative cross-national research capacity-building project taking place across Turkey and the Mediterranean Middle East (RESCAP-Med, funded by the EU). Identification of research capacity and training needs took place in three stages. The first stage involved mapping health institutions engaged in NCD research, based on a comprehensive literature review. The second stage entailed in-depth interviews with key informants (KIs) with an overview of research capacity in public health and the training needs of their staff. The third stage required interviewing junior researchers, identified by KIs in stage two, to evaluate their perceptions of their own training needs. The approach we have taken was based upon a method devised by Hennessy&#38;Hicks. In total, 55 junior researchers identified by 10 KIs were invited to participate, of whom 46 researchers agreed to take part (84%). The specific disciplines in public health identified in advance by RESCAP-MED for training were: advanced epidemiology, health economics, environmental health, medical sociology-anthropology, and health policy. Results The initial literature review showed considerable research on NCDs, but concentrated in a few areas of NCD research. The main problems listed by KIs were inadequate opportunities for specialization due to heavy teaching workloads, the lack of incentives to pursue research, a lack of financial resources even when interest existed, and insufficient institutional mechanisms for dialogue between policy makers and researchers over national research priorities. Among junior researchers, there was widespread competence in basic epidemiological skills, but an awareness of gaps in knowledge of more advanced epidemiological skills, and the opportunities to acquire these skills were lacking. Self-assessed competencies in each of the four other disciplines considered revealed greater training needs, especially regarding familiarity with the qualitative research skills for medical anthropology/sociology. Conclusions In Turkey there are considerable strengths to build upon. But a combination of institutional disincentives for research, and the lack of opportunities for the rising generation of researchers to acquire advanced training skills.</p

Two-scale analysis and design of spaceframes with complex additive manufactured nodes

The advancements in additive manufacturing (AM) technology have allowed for the production of geometrically complex parts with customizable designs. This versatility benefits large-scale space-frame structures, as the individual design of each structural node can be tailored to meet specific mechanical and other functional requirements. To this end, however, the design and analysis of such space-frames with distinct structural nodes needs to be highly automated. A critical aspect in this context is automated integration of the local 3D features into the 1D large-scale models. In the present work, a two-scale modeling approach is developed to improve the design and linear-elastic analysis of space frames with complex additively manufactured nodes. The mechanical characteristics of the 3D nodes are numerically reduced through an automated dimensional reduction process based on the Finite Cell Method (FCM) and substructuring. The reduced stiffness quantities are assembled in the large-scale 1D model which, in turn, enables efficient structural analysis. The response of the 1D model is passed on to the local model, enabling fully resolved 3D linear-elastic analysis. The proposed approach is numerically verified on a simplified beam example. Furthermore, the workflow is demonstrated on a tree canopy structure with additively manufactured nodes with bolted connections. The form of the large-scale structure is found based on the Combinatorial Equilibrium Modeling framework, and the different designs of the local structural nodes are based on generative exploration of the design space. It is demonstrated that the proposed methodology effectively automates the design and analysis of space-frame structures with complex, distinct structural nodes.Comment: 20 pages, 17 figure

Bolstering Stochastic Gradient Descent with Model Building

Stochastic gradient descent method and its variants constitute the core optimization algorithms that achieve good convergence rates for solving machine learning problems. These rates are obtained especially when these algorithms are fine-tuned for the application at hand. Although this tuning process can require large computational costs, recent work has shown that these costs can be reduced by line search methods that iteratively adjust the stepsize. We propose an alternative approach to stochastic line search by using a new algorithm based on forward step model building. This model building step incorporates second-order information that allows adjusting not only the stepsize but also the search direction. Noting that deep learning model parameters come in groups (layers of tensors), our method builds its model and calculates a new step for each parameter group. This novel diagonalization approach makes the selected step lengths adaptive. We provide convergence rate analysis, and experimentally show that the proposed algorithm achieves faster convergence and better generalization in well-known test problems. More precisely, SMB requires less tuning, and shows comparable performance to other adaptive methods

Parallel algorithms for nonlinear optimization

Parallel algorithm design is a very active research topic in optimization as parallel computer architectures have recently become easily accessible. This thesis is about an approach for designing parallel nonlinear programming algorithms. The main idea is to benefit from parallelization in designing new algorithms rather than considering direct parallelizations of the existing methods. We give a general framework following our approach, and then, give distinct algorithms that fit into this framework. The example algorithms we have designed either use procedures of existing methods within a multistart scheme, or they are completely new inherently parallel algorithms. In doing so, we try to show how it is possible to achieve parallelism in algorithm structure (at different levels) so that the resulting algorithms have a good solution performance in terms of robustness, quality of steps, and scalability. We complement our discussion with convergence proofs of the proposed algorithms

A Method for Minimizing the Phase Errors of Rotman Lenses

Abstract A method is introduced for determining the feed curves of Rotman lenses such that the phase errors are minimized. The method ensures that there are at least three zero phase error points on the radiating array for each off focal beam position. The results of a path length error study show that there is a very significant drop in the level of the maximum phase errors (in the order of about 4:1) compared with the commonly used circular and elliptical feed curves