932 resultados para Markov chains. Convergence. Evolutionary Strategy. Large Deviations


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Large-scale mechanical products, such as aircraft and rockets, consist of large numbers of small components, which introduce additional difficulty for assembly accuracy and error estimation. Planar surfaces as key product characteristics are usually utilised for positioning small components in the assembly process. This paper focuses on assembly accuracy analysis of small components with planar surfaces in large-scale volume products. To evaluate the accuracy of the assembly system, an error propagation model for measurement error and fixture error is proposed, based on the assumption that all errors are normally distributed. In this model, the general coordinate vector is adopted to represent the position of the components. The error transmission functions are simplified into a linear model, and the coordinates of the reference points are composed by theoretical value and random error. The installation of a Head-Up Display is taken as an example to analyse the assembly error of small components based on the propagation model. The result shows that the final coordination accuracy is mainly determined by measurement error of the planar surface in small components. To reduce the uncertainty of the plane measurement, an evaluation index of measurement strategy is presented. This index reflects the distribution of the sampling point set and can be calculated by an inertia moment matrix. Finally, a practical application is introduced for validating the evaluation index.

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A tanulmány célja, hogy azonosítsa azokat a tényezőket, amelyek befolyásolják az élelmiszer-gazdasági kis- és közepes vállalkozások szerződéseinek teljesülését a Közép-magyarországi régióban. Számításaink megerősítik Guo-Jolly [2008] eredményeit, amely szerint a szerződések tartalmi elemeinek kulcsszerepük van a szerződések teljesülésében. Továbbá a vállalatvezetői képességek, a vállalati és tranzakciós jellemzők szintén jelentős hatást gyakorolnak a szerződések teljesülésére. Érdekes módon az ágazatspecifikus jellemzőknek csak korlátozott szerepük van a szerződések teljesülésének magyarázatában. / === / The paper analyses the contractual relations and contract fulfilment of small and medium-sized firms along the food chain, in the central region of Hungary, using survey data. The estimates also reveal that contract fulfilment is significantly affected by the design of the contract. They confirm that an important role in contract fulfilment is played by corporate and managerial attributes and transaction characteristics. Interestingly, branch-specific characteristics play only a limited role in explaining contract fulfilment.

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A tanulmánykötet a globális értékláncok névvel fémjelezett jelenséget veszi górcső alá. A fókuszban a multinacionális vállalatcsoportok ill. a nemzetközi cégek állnak. A tíz tanulmány különböző megközelítések alapján betekintést ad abba, hogy hogyan ragadhatják meg és vizsgálhatják a kutatók a globális értékláncokat a vállalatok, ill. vezetőik nézőpontjából, mi következik a kutatási eredményekből a vállalatok vezetői számára, és milyen következményei vannak a globális értékláncok karakteres és terjedő jelenlétének a nemzetgazdaságok gazdasági politikáit formálókra. A tanulmánykötet szerzői a 2012/2013.tanév tavaszi félévében a Nemzetközi üzleti gazdaságtan c. PhD kurzus hallgatói voltak. ______ The working paper is to provide a Hungarian language overview on the research finding s on Global Value Chain and global factory. The phenomenon behind them is recognized but under researched in Hungary. The chapters of the working paper are to cover as many angles and perspectives of Global Value Chain as many it is possible. Each chapter is based on a published English language paper. Theoretical and conceptual issues, considerations of MNEs and small- and medium sized enterprises and that of national policies are discussed. Authors of the working paper attended the International Business PhD course in the spring semester of 2012/2013.

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This paper examines the recent history of the Hungarian energy trading market in a co-evolutionary framework. Hungary is characterized by a mixed ownership structure with mainly multinational incumbents in energy retail and distribution, while the wholesale is dominantly owned by state-owned companies. The legal framework also has dual characteristics, with free-market regulation for industrial consumers and a regulated price regime for households. Our research method follows a longitudinal approach from the period of market liberalization in 2008 until 2013. We identified strong relationship between the individual and sector performance of the trading companies and the current political ideology and institutional regime.

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A kereskedelmi láncok különböző stratégiákat választhatnak, illetve alkalmazhatnak a társadalmi, gazdasági és környezeti kihívások kezelésére, a társadalmi normákhoz és elvárásokhoz való igazodáshoz. A tanulmányban a szerző azt vizsgálja, hogy milyen összefüggés van a társadalmi felelősségvállalásuk és a versenyképességük között, s a felelős magatartásuk javítja-e versenypozíciójukat. Bemutatja, hogy hazai viszonylatban a nagyobb forgalmat lebonyolító kereskedelmi láncok milyen CSR-tevékenységet végeznek, ez beépült-e hosszabb távú üzleti stratégiájukba, és mennyiben járul/járulhat hozzá versenyképességük fokozásához. Elemzi több kereskedelmi láncnál, hogy miképpen sikerült összeegyeztetni társadalmi felelősségvállalásukat a profitérdekeltségükkel, továbbá megteremthető-e a felelős működésük és a költséghatékony gazdálkodásuk összhangja. Többek között rámutat arra, hogy a gazdasági és külső szociális felelősségvállalásuk, továbbá a versenyképességük közötti pozitív korreláció megkérdőjelezhetetlen, ami win-win szituációt alakít ki. ______ Commercial companies can embark on and apply different strategies to tackle social, economic and environmental challenges and to comply with the standards and expectations of the community. In the study the author analyses the relationship between corporate social responsibility activities and competitiveness, and whether or not the responsible attitude of these companies improves their competitive position. She outlines the CSR activities of high turnover commercial chains in Hungary, examining their incorporation into the company’s longer term business strategy, and how these activities may contribute to their enhanced competitiveness. She will analyse several commercial chains from the point of view of their success in harmonizing their CSR with their profit making, and whether they can create the harmony of an environmentally friendly attitude and cost-effective operations. Among other findings, the author concludes that there is an unquestionable correlation between corporate economic and outside social responsibility and profitability, which creates a definite win-win situation.

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The major barrier to practical optimization of pavement preservation programming has always been that for formulations where the identity of individual projects is preserved, the solution space grows exponentially with the problem size to an extent where it can become unmanageable by the traditional analytical optimization techniques within reasonable limit. This has been attributed to the problem of combinatorial explosion that is, exponential growth of the number of combinations. The relatively large number of constraints often presents in a real-life pavement preservation programming problems and the trade-off considerations required between preventive maintenance, rehabilitation and reconstruction, present yet another factor that contributes to the solution complexity. In this research study, a new integrated multi-year optimization procedure was developed to solve network level pavement preservation programming problems, through cost-effectiveness based evolutionary programming analysis, using the Shuffled Complex Evolution (SCE) algorithm.^ A case study problem was analyzed to illustrate the robustness and consistency of the SCE technique in solving network level pavement preservation problems. The output from this program is a list of maintenance and rehabilitation treatment (M&R) strategies for each identified segment of the network in each programming year, and the impact on the overall performance of the network, in terms of the performance levels of the recommended optimal M&R strategy. ^ The results show that the SCE is very efficient and consistent in the simultaneous consideration of the trade-off between various pavement preservation strategies, while preserving the identity of the individual network segments. The flexibility of the technique is also demonstrated, in the sense that, by suitably coding the problem parameters, it can be used to solve several forms of pavement management programming problems. It is recommended that for large networks, some sort of decomposition technique should be applied to aggregate sections, which exhibit similar performance characteristics into links, such that whatever M&R alternative is recommended for a link can be applied to all the sections connected to it. In this way the problem size, and hence the solution time, can be greatly reduced to a more manageable solution space. ^ The study concludes that the robust search characteristics of SCE are well suited for solving the combinatorial problems in long-term network level pavement M&R programming and provides a rich area for future research. ^

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In his dialogue - Near Term Computer Management Strategy For Hospitality Managers and Computer System Vendors - by William O'Brien, Associate Professor, School of Hospitality Management at Florida International University, Associate Professor O’Brien initially states: “The computer revolution has only just begun. Rapid improvement in hardware will continue into the foreseeable future; over the last five years it has set the stage for more significant improvements in software technology still to come. John Naisbitt's information electronics economy¹ based on the creation and distribution of information has already arrived and as computer devices improve, hospitality managers will increasingly do at least a portion of their work with software tools.” At the time of this writing Assistant Professor O’Brien will have you know, contrary to what some people might think, the computer revolution is not over, it’s just beginning; it’s just an embryo. Computer technology will only continue to develop and expand, says O’Brien with citation. “A complacent few of us who feel “we have survived the computer revolution” will miss opportunities as a new wave of technology moves through the hospitality industry,” says ‘Professor O’Brien. “Both managers who buy technology and vendors who sell it can profit from strategy based on understanding the wave of technological innovation,” is his informed opinion. Property managers who embrace rather than eschew innovation, in this case computer technology, will benefit greatly from this new science in hospitality management, O’Brien says. “The manager who is not alert to or misunderstands the nature of this wave of innovation will be the constant victim of technology,” he advises. On the vendor side of the equation, O’Brien observes, “Computer-wise hospitality managers want systems which are easier and more profitable to operate. Some view their own industry as being somewhat behind the times… They plan to pay significantly less for better computer devices. Their high expectations are fed by vendor marketing efforts…” he says. O’Brien warns against taking a gamble on a risky computer system by falling victim to un-substantiated claims and pie-in-the-sky promises. He recommends affiliating with turn-key vendors who provide hardware, software, and training, or soliciting the help of large mainstream vendors such as IBM, NCR, or Apple. Many experts agree that the computer revolution has merely and genuinely morphed into the software revolution, informs O’Brien; “…recognizing that a computer is nothing but a box in which programs run.” Yes, some of the empirical data in this article is dated by now, but the core philosophy of advancing technology, and properties continually tapping current knowledge is sound.

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In his dialogue titled - Overcoming The Impotency Of Marketing - K. Michael Haywood, Assistant Professor, School of Hotel and Food Administration, University of Guelph, originally reveals: “Many accommodation businesses have discovered that their marketing activities are becoming increasingly impotent. To overcome this evolutionary stage in the life cycle of marketing, this article outlines six principles that will re-establish marketing's vitality.” “The opinion of general managers and senior marketing, financial, and food and beverage managers is that the marketing is not producing the results it once did and is not working as it should,” Haywood advises. Haywood points to price as the primary component hospitality managers use to favor/adjust their marketability. Although this is an effective tool, the practice can also erode profitability and margin he says. Haywood also points at recession as a major factor in exposing the failures of marketing plans. He adds that the hotel manager cannot afford to let this rationale go unchallenged; managers must take measures to mitigate circumstances that they might not have any control over. Managers must attempt to maintain profitability. “In many hotels, large corporate accounts or convention business generates a significant proportion of occupancy. Often these big buyers dictate their terms to the hotels, especially the price they are prepared to pay and the service they expect,” Haywood warns. This dynamic is just another significant pitfall that challenges marketing strategy. The savvy marketing technician must be aware of changes that occur in his or her marketplace, Haywood stresses. He offers three specific, real changes, which should be responded to. “To cope with the problems and uncertainties of the hotel business during the remainder of the decade, six components need to be developed if marketing impotency is to be overcome,” says Haywood in outlining his six-step approach to the problem. Additionally, forward thinking cannot be over-emphasized. “A high market share is helpful in general, but an even more crucial factor is careful consideration of the market sectors in which the company wants to operate,” your author advises. “Taking tactical initiatives is essential. Successful hotels act; unsuccessful ones react. The less successful marketing operations tend to be a hive of frantic activity. Fire-fighting is the normal way of life in such organizations, Haywood observes. “By contrast, successful firms plan and execute their tactical marketing activity with careful timing and precision so as to create the maximum impact,” he extends in describing his fruitful marketing arabesque.

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Water-alternating-gas (WAG) is an enhanced oil recovery method combining the improved macroscopic sweep of water flooding with the improved microscopic displacement of gas injection. The optimal design of the WAG parameters is usually based on numerical reservoir simulation via trial and error, limited by the reservoir engineer’s availability. Employing optimisation techniques can guide the simulation runs and reduce the number of function evaluations. In this study, robust evolutionary algorithms are utilized to optimise hydrocarbon WAG performance in the E-segment of the Norne field. The first objective function is selected to be the net present value (NPV) and two global semi-random search strategies, a genetic algorithm (GA) and particle swarm optimisation (PSO) are tested on different case studies with different numbers of controlling variables which are sampled from the set of water and gas injection rates, bottom-hole pressures of the oil production wells, cycle ratio, cycle time, the composition of the injected hydrocarbon gas (miscible/immiscible WAG) and the total WAG period. In progressive experiments, the number of decision-making variables is increased, increasing the problem complexity while potentially improving the efficacy of the WAG process. The second objective function is selected to be the incremental recovery factor (IRF) within a fixed total WAG simulation time and it is optimised using the same optimisation algorithms. The results from the two optimisation techniques are analyzed and their performance, convergence speed and the quality of the optimal solutions found by the algorithms in multiple trials are compared for each experiment. The distinctions between the optimal WAG parameters resulting from NPV and oil recovery optimisation are also examined. This is the first known work optimising over this complete set of WAG variables. The first use of PSO to optimise a WAG project at the field scale is also illustrated. Compared to the reference cases, the best overall values of the objective functions found by GA and PSO were 13.8% and 14.2% higher, respectively, if NPV is optimised over all the above variables, and 14.2% and 16.2% higher, respectively, if IRF is optimised.

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From the 12th until the 17th of July 2016, research vessel Maria S. Merian entered the Nordvestfjord of Scorsby Sound (East Greenland) as part of research cruise MSM56, "Ecological chemistry in Arctic fjords". A large variety of chemical and biological parameters of fjord and meltwater were measured during this cruise to characterize biogeochemical fluxes in arctic fjords. The photo documentation described here was a side project. It was started when we were close to the Daugaard-Jensen glacier at the end of the Nordvestfjord and realized that not many people have seen this area before and photos available for scientists are probably rare. These pictures shall help to document climate and landscape changes in a remote area of East Greenland. Pictures were taken with a Panasonic Lumix G6 equipped with either a 14-42 or 45-150 objective (zoom factor available in jpg metadata). Polarizer filters were used on both objectives. The time between taking the pictures and writing down the coordinates was maximally one minute but usually shorter. The uncertainty in position is therefore small as we were steaming slowly most of the time the pictures were taken (i.e. below 5 knots). I assume the uncertainty is in most cases below 200 m radius of the noted position. I did not check the direction I directed the camera to with a compass at the beginning. Hence, the direction that was noted is an approximation based on the navigation map and the positioning of the ship. The uncertainty was probably around +/- 40° but initially (pictures 1-17) perhaps even higher as this documentation was a spontaneous idea and it took some time to get the orientation right. It should be easy, however, to find the location of the mountains and glaciers when being on the respective positions because the mountains have a quite characteristic shape. In a later stage of this documentation, I took pictures from the bridge and used the gyros to approximate the direction the camera was pointed at. Here the uncertainty was much lower (i.e. +/- 20° or better). Directions approximated with the help of gyros have degree values in the overview table. The ship data provided in the MSM56 cruise report will contain all kinds of sensor data from Maria S. Merian sensor setup. This data can also be used to further constrain the position the pictures were taken because the exact time a photo was shot is noted in the metadata of the .jpg photo file. The shipboard clock was set on UTC. It was 57 minutes and 45 seconds behind the time in the camera. For example 12:57:45 on the camera was 12:00:00 UTC on the ship. All pictures provided here can be used for scientific purposes. In case of usage in presentations etc. please acknowledge RV Maria S. Merian (MSM56) and Lennart T. Bach as author. Please inform me and ask for reprint permission in case you want to use the pictures for scientific publications. I would like to thank all participants and the crew of Maria S. Merian Cruise 56 (MSM56, Ecological chemistry in Arctic fjords).

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Globalization and technological changes that has happened since the 80s have brought remarkable changes in the industrial and commercial paradigm, which are expressed mainly in the international fragmentation of production and in the formation of Global Value Chains (GVC). This thesis sought to understand such phenomena and discuss new relevant variables in this context for a more accurate analysis of the current trade patterns not addressed by the seminal economic theories that relate trade and economic growth. It sought to evaluate how the trade specialization pattern of Brazil evolved compared to other economies (China, India, Russia, United States, Japan and selected Latin American economies) in the light of these phenomena from 1995 to 2011. Therefore, we have used the methodology of gross exports decomposition in value added measures, developed by Koopman et al. (2014), and indicators estimated from data of two global matrices I-O: a WIOT (2013) and the TiVA (2015). It was also tested two hypotheses regarding the role of these phenomena as determinants of economic growth in recent years: 1º) fragmentation and participation in GVC ensure higher growth rates for countries; 2º) the place (stage) in which the country finds itself in GVC associated with sectoral technological aspects is also important for economic growth. For this, we used dynamic panel models (Difference GMM and System GMM) for a sample of 40 countries from 2003 to 2011. The studies carried out on Brazil show that the country is no longer on the margins of these phenomena, because it shows increasing rates of participation in GVC, including in sectors considered most strategic for fragmentation. However, there is not a standard convergence of trade specialization of the country to those presented by developed countries or movements earned by China and Mexico in terms of their position and profile of participating in GVC. Another important result obtained by the thesis is the identification of these phenomena are in fact new variables relevant for economic growth, because it shows empirical evidences to support the hypothesis 1 and, partially, the hypothesis 2. A joint analysis of the estimated econometric results with the results of the descriptive analysis of the Brazilian economy, it leads us to conclude that the trade specialization pattern of the country in the context of the new trade setups is presented unfavorably to its growth strategy.

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Large marine areas and regional seas present a challenge in terms of management. They are often bordered by numerous maritime jurisdictions; with multi-use and multi-sector environments; involving varying governance arrangements; and generation of sufficient levels of data to best inform decision-makers. Marine management at the regional scale involves a range of mechanisms and approaches to ensure all relevant stakeholders have an opportunity to engage in the process; and these approaches can differ in their legal and regulatory conditions. At present, no such comparable structures exist at the transnational level for the ecosystem-based management of the Celtic Sea. Against this backdrop, a participative process, involving representatives from differing sectors of activity in the Celtic Sea spanning four Member States, was established for the purpose of identifying realistic and meaningful management principles in line with the goals of the Marine Strategy Framework Directive.

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We report the results of direct measurement of remanent hysteresis loops on nanochains of BiFeO3 at room temperature under zero and ∼20 kOe magnetic field. We noticed a suppression of remanent polarization by nearly ∼40% under the magnetic field. The powder neutron diffraction data reveal significant ion displacements under a magnetic field which seems to be the origin of the suppression of polarization. The isolated nanoparticles, comprising the chains, exhibit evolution of ferroelectric domains under dc electric field and complete 180 switching in switching-spectroscopy piezoresponse force microscopy. They also exhibit stronger ferromagnetism with nearly an order of magnitude higher saturation magnetization than that of the bulk sample. These results show that the nanoscale BiFeO3 exhibits coexistence of ferroelectric and ferromagnetic order and a strong magnetoelectric multiferroic coupling at room temperature comparable to what some of the type-II multiferroics show at a very low temperature.

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Fitting statistical models is computationally challenging when the sample size or the dimension of the dataset is huge. An attractive approach for down-scaling the problem size is to first partition the dataset into subsets and then fit using distributed algorithms. The dataset can be partitioned either horizontally (in the sample space) or vertically (in the feature space), and the challenge arise in defining an algorithm with low communication, theoretical guarantees and excellent practical performance in general settings. For sample space partitioning, I propose a MEdian Selection Subset AGgregation Estimator ({\em message}) algorithm for solving these issues. The algorithm applies feature selection in parallel for each subset using regularized regression or Bayesian variable selection method, calculates the `median' feature inclusion index, estimates coefficients for the selected features in parallel for each subset, and then averages these estimates. The algorithm is simple, involves very minimal communication, scales efficiently in sample size, and has theoretical guarantees. I provide extensive experiments to show excellent performance in feature selection, estimation, prediction, and computation time relative to usual competitors.

While sample space partitioning is useful in handling datasets with large sample size, feature space partitioning is more effective when the data dimension is high. Existing methods for partitioning features, however, are either vulnerable to high correlations or inefficient in reducing the model dimension. In the thesis, I propose a new embarrassingly parallel framework named {\em DECO} for distributed variable selection and parameter estimation. In {\em DECO}, variables are first partitioned and allocated to m distributed workers. The decorrelated subset data within each worker are then fitted via any algorithm designed for high-dimensional problems. We show that by incorporating the decorrelation step, DECO can achieve consistent variable selection and parameter estimation on each subset with (almost) no assumptions. In addition, the convergence rate is nearly minimax optimal for both sparse and weakly sparse models and does NOT depend on the partition number m. Extensive numerical experiments are provided to illustrate the performance of the new framework.

For datasets with both large sample sizes and high dimensionality, I propose a new "divided-and-conquer" framework {\em DEME} (DECO-message) by leveraging both the {\em DECO} and the {\em message} algorithm. The new framework first partitions the dataset in the sample space into row cubes using {\em message} and then partition the feature space of the cubes using {\em DECO}. This procedure is equivalent to partitioning the original data matrix into multiple small blocks, each with a feasible size that can be stored and fitted in a computer in parallel. The results are then synthezied via the {\em DECO} and {\em message} algorithm in a reverse order to produce the final output. The whole framework is extremely scalable.

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People go through their life making all kinds of decisions, and some of these decisions affect their demand for transportation, for example, their choices of where to live and where to work, how and when to travel and which route to take. Transport related choices are typically time dependent and characterized by large number of alternatives that can be spatially correlated. This thesis deals with models that can be used to analyze and predict discrete choices in large-scale networks. The proposed models and methods are highly relevant for, but not limited to, transport applications. We model decisions as sequences of choices within the dynamic discrete choice framework, also known as parametric Markov decision processes. Such models are known to be difficult to estimate and to apply to make predictions because dynamic programming problems need to be solved in order to compute choice probabilities. In this thesis we show that it is possible to explore the network structure and the flexibility of dynamic programming so that the dynamic discrete choice modeling approach is not only useful to model time dependent choices, but also makes it easier to model large-scale static choices. The thesis consists of seven articles containing a number of models and methods for estimating, applying and testing large-scale discrete choice models. In the following we group the contributions under three themes: route choice modeling, large-scale multivariate extreme value (MEV) model estimation and nonlinear optimization algorithms. Five articles are related to route choice modeling. We propose different dynamic discrete choice models that allow paths to be correlated based on the MEV and mixed logit models. The resulting route choice models become expensive to estimate and we deal with this challenge by proposing innovative methods that allow to reduce the estimation cost. For example, we propose a decomposition method that not only opens up for possibility of mixing, but also speeds up the estimation for simple logit models, which has implications also for traffic simulation. Moreover, we compare the utility maximization and regret minimization decision rules, and we propose a misspecification test for logit-based route choice models. The second theme is related to the estimation of static discrete choice models with large choice sets. We establish that a class of MEV models can be reformulated as dynamic discrete choice models on the networks of correlation structures. These dynamic models can then be estimated quickly using dynamic programming techniques and an efficient nonlinear optimization algorithm. Finally, the third theme focuses on structured quasi-Newton techniques for estimating discrete choice models by maximum likelihood. We examine and adapt switching methods that can be easily integrated into usual optimization algorithms (line search and trust region) to accelerate the estimation process. The proposed dynamic discrete choice models and estimation methods can be used in various discrete choice applications. In the area of big data analytics, models that can deal with large choice sets and sequential choices are important. Our research can therefore be of interest in various demand analysis applications (predictive analytics) or can be integrated with optimization models (prescriptive analytics). Furthermore, our studies indicate the potential of dynamic programming techniques in this context, even for static models, which opens up a variety of future research directions.