We develop methods for solving nonlinear stochasticdynamic difference games using orthogonal polynomial collocation techniques. The methods are applied to models of world commodity markets in which governments compet...
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We develop methods for solving nonlinear stochasticdynamic difference games using orthogonal polynomial collocation techniques. The methods are applied to models of world commodity markets in which governments compete against each other using storage as a strategy variable. The rational expectations equilibrium outcomes under four different game structures are derived numerically and compared using stochastic simulation techniques.
Shifting freight volumes from road to rail transport increases the economic performances of freight logistics. However, compared to road transport, rail transport generally lacks the flexibility in delivery quantity a...
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Shifting freight volumes from road to rail transport increases the economic performances of freight logistics. However, compared to road transport, rail transport generally lacks the flexibility in delivery quantity and frequency, and exhibits economies of scale in its shipment volume. This often leads to high inventory levels in the destination after deliveries. We generalize the tailored base-surge dual sourcing inventory model by introducing a fixed cost in rail transport, adding an extra decision in its delivery frequency, and relaxing the assumption of the base stock control of road transport, to support firms' modal split transport optimization. The objective is to optimize the controls of the two transport modes and the corresponding inventory management at the destination, which minimize the combined average transport and inventory costs per period in the steady state. Using stochastic dynamic programming, we find that when the delivery quantity and frequency of rail transport is fixed, the optimal shipment volume via the road transport indeed follows a base stock control. This allows to solve the relevant Bellman equation via an efficient policy iteration approach. We also find that the total cost is convex in the delivery quantity of rail transport, and a bi-section search can be applied. Finally, we analyze the sensitivity and robustness of our model using values suggested by a consumer goods firm. (C) 2019 Elsevier B.V. All rights reserved.
When software reliability demonstration of safety-critical systems by statistical testing is treated as a Test, Analyse and Fix (TAAF) process, an optimal testing policy can be found, which maximises the probability o...
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When software reliability demonstration of safety-critical systems by statistical testing is treated as a Test, Analyse and Fix (TAAF) process, an optimal testing policy can be found, which maximises the probability of p success of the whole process, over a pre-determined period of time. The optimisation problem is formulated, solved by stochastic dynamic programming, and demonstrated by two numerical examples. (C) 2002 Elsevier Science B.V. All rights reserved.
One of the most important operations in the production of growing/finishing pigs is the marketing of pigs for slaughter. While pork production can be managed at different levels (animal, pen, section, or herd), it is ...
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One of the most important operations in the production of growing/finishing pigs is the marketing of pigs for slaughter. While pork production can be managed at different levels (animal, pen, section, or herd), it is beneficial to consider the herd level when determining the optimal marketing policy due to inter-dependencies, such as those created by fixed transportation costs and cross-level constraints. In this paper, we consider sequential marketing decisions at herd level. A high-dimensional infinite horizon Markov decision process (MDP) is formulated which, due to the curse of dimensionality, cannot be solved using standard MDP optimization techniques. Instead, approximate dynamicprogramming (ADP) is applied to solve the model and find the best marketing policy at herd level. Under the total expected discounted reward criterion, the proposed ADP approach is first compared with a standard solution algorithm for solving an MDP at pen level to show the accuracy of the solution procedure. Next, numerical experiments at herd level are given to confirm how the marketing policy adapts itself to varying costs (e.g., transportation cost) and cross-level constraints. Finally, a sensitivity analysis for some parameters in the model is conducted and the marketing policy found by ADP is compared with other well-known marketing polices, often applied at herd level. (C) 2019 Elsevier B.V. All rights reserved.
Directed hypergraphs represent a general modelling and algorithmic tool, which have been successfully used in many different research areas such as artificial intelligence, database systems, fuzzy systems, proposition...
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Directed hypergraphs represent a general modelling and algorithmic tool, which have been successfully used in many different research areas such as artificial intelligence, database systems, fuzzy systems, propositional logic and transportation networks. However, modelling Markov decision processes using directed hypergraphs has not yet been considered. In this paper we consider finite-horizon Markov decision processes (MDPs) with finite state and action space and present an algorithm for finding the K best deterministic Markov policies. That is, we are interested in ranking the first K deterministic Markov policies in non-decreasing order using an additive criterion of optimality. The algorithm uses a directed hypergraph to model the finite-horizon MDP. It is shown that the problem of finding the optimal policy can be formulated as a minimum weight hyperpath problem and be solved in linear time, with respect to the input data representing the MDP, using different additive optimality criteria. (c) 2005 Elsevier B.V. All rights reserved.
The challenging issue of "human-machine copilot" opens up a new frontier to enhancing driving safety. However, driver-machine conflicts and uncertain driver/external disturbances are significant problems in ...
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The challenging issue of "human-machine copilot" opens up a new frontier to enhancing driving safety. However, driver-machine conflicts and uncertain driver/external disturbances are significant problems in cooperative steering systems, which degrade the system's path-tracking ability and reduce driving safety. This paper proposes a novel stochastic game-based shared control framework to model the steering torque interaction between the driver and the intelligent electric power steering (IEPS) system. A six-order driver-vehicle dynamic system, including driver/external uncertainty, is established for path-tracking. Then, the affine linear-quadratic-based path-tracking problem is proposed to model the maneuvers of the driver and IEPS. Particularly, the feedback Nash and Stackelberg frameworks to the affine-quadratic problem are derived by stochastic dynamic programming. Two cases of copilot lane change driving scenarios are studied via computer simulation. The intrinsic relation between the stochastic Nash and Stackelberg strategies is investigated based on the results. And the steering-in-the-loop experiment reveals the potential of the proposed shared control framework in handling driver-IEPS conflicts and uncertain driver/external turbulence. Finally, the copiloting experiments with a human driver further demonstrate the rationality of the game-based pattern between both the agents.
A new adaptive intermittent maneuver strategy is proposed, which has switching threshold levels dependent on the estimated time-to-go for dual-control guidance of passive homing missiles. Guidance performance in terms...
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A new adaptive intermittent maneuver strategy is proposed, which has switching threshold levels dependent on the estimated time-to-go for dual-control guidance of passive homing missiles. Guidance performance in terms of control effort and target observability for the adaptive intermittent maneuver strategy are also analyzed, as well as proportional navigation guidance. With intermittent maneuvers the guidance command is occasionally disabled to intentionally increase guidance errors. When provided with suitable switching threshold levels, this intermittent maneuver strategy improves target observability and, consequently, intercept performance. Statistical simulations for an atmospheric engagement demonstrate the effectiveness of the proposed intermittent maneuver strategy.
Managerial flexibility has value in the context of uncertain R&D projects, as management can repeatedly gather information about uncertain project and market characteristics and, based on this information, change ...
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Managerial flexibility has value in the context of uncertain R&D projects, as management can repeatedly gather information about uncertain project and market characteristics and, based on this information, change its course of action. This value is now well accepted and referred to as "real option value." We introduce, in addition to the familiar real option of abandonment, the option of corrective action that management can take during the project. The intuition from options pricing theory is that higher uncertainty in project pay offs increases the real option value of managerial decision flexibility. However, R&D managers face uncertainty not only in payoffs, but also from many other sources. We identify five example types of R&D uncertainty, in market payoffs, project budgets, product performance, market requirements, and project schedules. How do they influence the value from managerial flexibility? We find that if uncertainty is resolved or costs/revenues occur after all decisions have been made, more variability may "smear out" contingencies and thus reduce the value of flexibility In addition, variability may reduce the probability of flexibility ever being exercised, which also reduces its value. This result runs counter to established option pricing theory intuition and contributes to a better risk management in R&D projects. Our model builds intuition for R&D managers as to when it is and when it is not worthwhile to delay commitments-for example, by postponing a design freeze, thus maintaining flexibility in R&D projects.
In this correspondence, we study the problem of finding optimal reconfiguration strategies for a class of reconfigurable fault- tolerant computer systems in which there is no repair in failed components. The problem o...
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In this correspondence, we study the problem of finding optimal reconfiguration strategies for a class of reconfigurable fault- tolerant computer systems in which there is no repair in failed components. The problem of finding optimal reconfiguration strategies consists of determining, for each failed state of the system, the operational state into which the system should reconfigure itself. We presented a stochastic model for the above class of reconfigurable computer systems. Based on this model, we construct a polynomial-time algorithm for finding optimal reconfiguration strategies.
We consider an optimization problem for finite queues governed by priority-discarding control policies. We develop an analytical model for systems that defer discarding decisions until service completion instants, but...
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We consider an optimization problem for finite queues governed by priority-discarding control policies. We develop an analytical model for systems that defer discarding decisions until service completion instants, but then may expel any waiting jobs. Using stochastic dynamic programming techniques, we obtain closed-form optimization results for systems constrained to retain at most one job. Numerical performance examples are included.
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