Preconditioning Newton-Krylov Methods in Non-Convex Large Scale Optimization

We consider an iterative preconditioning technique for non-convex large scale optimization. First, we refer to the solution of large scale indefinite linear systems by using a Krylov subspace method, and describe the iterative construction of a preconditioner which does not involve matrices products or matrices storage. The set of directions generated by the Krylov subspace method is used, as by product, to provide an approximate inverse preconditioner. Then, we experience our preconditioner within Truncated Newton schemes for large scale unconstrained optimization, where we generalize the truncation rule by Nash–Sofer (Oper. Res. Lett. 9:219–221, 1990) to the indefinite case, too. We use a Krylov subspace method to both approximately solve the Newton equation and to construct the preconditioner to be used at the current outer iteration. An extensive numerical experience shows that the proposed preconditioning strategy, compared with the unpreconditioned strategy and PREQN (Morales and Nocedal in SIAM J. Optim. 10:1079–1096, 2000), may lead to a reduction of the overall inner iterations. Finally, we show that our proposal has some similarities with the Limited Memory Preconditioners (Gratton et al. in SIAM J. Optim. 21:912–935, 2011)

Digital game elements, user experience and learning

The primary aim of this paper is to identify and theoretically validate the relationships between core game design elements and mechanics, user motivation and engagement and consequently learning. Additionally, it tries to highlight the moderating role of player personality traits on learning outcomes and acceptance and suggest ways to incorporate them in the game design process. To that end, it outlines the role of narrative, aesthetics and core game mechanics in facilitating higher learning outcomes through intrinsic motivation and engagement. At the same time, it discusses how player goal orientation, openness to experience, conscientiousness, sensation seeking and need for cognition influence the translation of the gameplay experience into valuable learning outcomes and user acceptance of the technology

Determination and sensitivity analysis of the seismic velocity of a shallow layer from refraction traveltimes measures

In this paper, we are interested in determining the seismic velocity of ashallow under-ground layer from refraction traveltimes measures. Wepresent a study case taken from an experimental seismic survey. The studycase is a wide-angle seismic inversion using experimental traveltimesmeasures and based on ray tracing technique and genetic algorithms. Thehypothesis on the velocity distribution, coming from the seismicexperiment, makes the computation of some seismic rays expensive intime. We propose to reduce the computations time by introducing aformulation of the inverse problem that avoids such costly rays, hence theinversion becomes feasible.Also we present a sensitivity analysis based on a singular valuedecomposition of the jacobian of the traveltimes with respect to velocity.We give the relationship between the traveltimes measure errors and thevelocity estimation error. We discuss the advantages of this method overthe classical one based on the resolution matrix

Utilization of antenna arrays in HF systems

Different applications of radio systems are based on the implementation of antenna arrays. Classically, radio direction finding operates with a multi channel receiving system connected to an array of receiving antennas. More recently, MIMO architectures have been proposed to increase the capacity of radio links by the use of antenna arrays at both the transmitter and receiver. The first part of this paper describes some novel experimental work carried out to examine the feasibility of applying MIMO techniques for communications within the HF radio band. A detailed correlation analysis of a variety of different antenna array configurations is presented. The second section of the paper also deals with HF MIMO communications, focusing on the problem from a modelling point of view. The third part presents a sensitivity analysis of different antenna array structures for HF direction finding applications. The results demonstrate that when modelling errors, heterogeneous antenna arrays are more robust in comparison to homogeneous structures