What can be inferred from surrogate data testing?

Surrogate data testing for linearity is frequently applied to confirm the results of nonlinear time series analysis. We argue that this, in general, is not possible.Comment: 1 pag

When should you press the reload button?

While surfing on the Internet, you may have observed the following. If a webpage takes a long time to download and you press the reload button then often the page promptly appears on your screen. Hence, the download was not hindered by congestion — then you’d better try again later — but by some other cause.\ud If you do not know if some cause (like congestion) may hinder your download then what is a good strategy? When should you cancel the download and when should you press the reload button? Should you press it immediately or should you wait for a while? And how long should you wait before cancelling the download? We analyze these issues in this article, which is a non-technical impression of the paper “Efficiency of Repeated Network Interactions” [4] by Judith Timmer (UT) and Michel Mandjes (UvA).\u

Actual Test Coverage for Embedded Systems

Testing embedded systems is inherently incomplete; no test suite will ever be able to test all possible usage scenarios. Therefore, in the past decades many coverage measures have been developed. These measures denote the portion of a system that is tested, that way providing a quality criterion for test suites. Formulating coverage criteria is not an easy task. The measures provided in the literature are consequently almost all very trivial and syntax-dependent. Well-known examples are statement and path coverage in white-box testing, and state and transition coverage in black-box testing. The complexity of designing coverage measures for embedded systems is contained in the highly dynamic behaviour of such systems, which is state-dependent and subject to many interleavings. In this talk we introduce a framework on actual test coverage. This measure denotes the number of faults actually shown present or absent. Our framework contains a method to evaluate the actual coverage of a given set of test suite executions after testing has taken place, providing a means to express the quality of a testing process. It also contains a method to predict the actual coverage a certain number of executions will yield, providing a means to select the best test suite. Both the evaluation afterwards and the prediction in advance are quite efficient, making it feasible to implement the theory in a tool and use it in a practical context

SCOOP: A Tool for SymboliC Optimisations Of Probabilistic Processes

This paper presents SCOOP: a tool that symbolically optimises process-algebraic specifications of probabilistic processes. It takes specifications in the prCRL language (combining data and probabilities), which are linearised first to an intermediate format: the LPPE. On this format, optimisations such as dead-variable reduction and confluence reduction are applied automatically by SCOOP. That way, drastic state space reductions are achieved while never having to generate the complete state space, as data variables are unfolded only locally. The optimised state spaces are ready to be analysed by for instance CADP or PRISM

A coordination mechanism with fair cost allocation for divergent multi-echelon inventory systems

This paper is concerned with the coordination of inventory control in divergent multiechelon inventory systems under periodic review and decentralized control. All the installations track echelon inventories. Under decentralized control the installations will decide upon replenishment policies that minimize their individual inventory costs. In general these policies do not coincide with the optimal policies of the system under centralized control. Hence, the total cost under decentralized control is larger than under centralized control.\ud To remove this cost inefficiency, a simple coordination mechanism is presented that is initiated by the most downstream installations. The upstream installation increases its base stock level while the downstream installation compensates the upstream one for increased costs and provides it with additional side payments. We show that this mechanism coordinates the system; the global optimal policy of the system is the unique Nash equilibrium of the corresponding strategic game. Furthermore, the mechanism results in a fair allocation of the costs; all installations enjoy cost savings

The effects of win-win conditions on revenue-sharing contracts

This paper studies revenue-sharing contracts in distribution chains in the presence of win-win conditions. Revenue-sharing contracts are a mechanism to coordinate the firms in a distribution chain. Under these contracts the retailer shares its revenue with the supplier in exchange for a lower wholesale price. The win-win conditions are natural conditions requiring that the profit of any firm may not decrease after implementing the revenue-sharing contract. If these conditions are not met, that is, if at least one firm is confronted with decreased profits, the firms will not agree upon signing the contract and the revenue-sharing contract will not be implemented. We show that the win-win conditions result in a smaller range of contracts being offered by the supplier. More important, in case of multiple competing retailers there may be no revenue-sharing contract satisfying these conditions. Hence, in the presence of win-win conditions revenue-sharing contracts are not suitable for distribution chains with a supplier and multiple competing retailers. For these chains we present a simple alternative coordination mechanism that coordinates the chain and satisfies all win-win conditions. \u

Supermarkets, Modern Supply Chains, and the Changing Food Policy Agenda

There is great interest among policy makers in how to influence the behavior of supermarkets in ways that serve the interests of important groups in society, especially small farmers and the owners of traditional, small-scale food wholesale and retail facilities. Two broader issues are also important: (1) finding a way for food prices to “internalize” the full environmental costs of production and marketing; and (2) finding a way for supermarkets to be part of the solution, rather than part of the problem, to the health problems generated by an “affluent” diet and lifestyle. There are concerns over the growing concentration in global food retailing and the potential market power that concentration implies. But the evidence of fierce competition at the retail level, and the high contestability for food consumers’ dollars, have kept this issue in the background. The ultimate impact of supermarkets in developing countries will be on the level and distribution of improved welfare for consumers. What happens to small farmers, traditional traders and mom-and-pop shops will be factors in both the size of welfare gains and their distribution, but many other factors will also come into play. Our judgment on the impact of the supermarket revolution must incorporate all of those factors. This paper places the supermarket debate in the broader evolution of food policy analysis, which is a framework for integrating household, market, macro and trade issues as they affect hunger and poverty. Increasingly, supermarkets provide the institutional linkages across these issues.Food policy; agricultural diversification; structural transformation; poverty

The Compromise Value for Cooperative Games with Random Payoffs

AMS classification: 90D12;cooperative games