IST Austria Technical Report

We consider the problem of expected cost analysis over nondeterministic probabilistic programs, which aims at automated methods for analyzing the resource-usage of such programs. Previous approaches for this problem could only handle nonnegative bounded costs. However, in many scenarios, such as queuing networks or analysis of cryptocurrency protocols, both positive and negative costs are necessary and the costs are unbounded as well. In this work, we present a sound and efficient approach to obtain polynomial bounds on the expected accumulated cost of nondeterministic probabilistic programs. Our approach can handle (a) general positive and negative costs with bounded updates in variables; and (b) nonnegative costs with general updates to variables. We show that several natural examples which could not be handled by previous approaches are captured in our framework. Moreover, our approach leads to an efficient polynomial-time algorithm, while no previous approach for cost analysis of probabilistic programs could guarantee polynomial runtime. Finally, we show the effectiveness of our approach by presenting experimental results on a variety of programs, motivated by real-world applications, for which we efficiently synthesize tight resource-usage bounds

The role of agricultural entrepreneurship in Dutch agriculture of today

It is thought that agricultural entrepreneurs have an important role to play in Dutch agriculture. They are currently being confronted with drastic changes and it is open to question whether or not they are willing and able to deal with such changes. A telephone survey was carried out in order to find an answer to this question. The data presented here are based on the answers from 752 farmers. The questions to be answered were: (1) Which strategies do agricultural entrepreneurs choose to keep up with business demands? (2) Which personal characteristics are related to these choices and to successful agricultural entrepreneurship in general? (3) Do agricultural entrepreneurs in the Netherlands meet the demands of "real" entrepreneurship according to economic theories? Agricultural entrepreneurship was conceptualized into the strategic orientations, social orientation, growth orientation, and financial conservatism. The data showed that five different types of farmers could be distinguished on the basis of their preferences for different strategic orientations. Social farmers had especially high scores for social orientation, traditional growers for growth orientation, prudent farmers for financial conservatism, new growers for both social orientation and growth orientation, and indecisive farmers for all strategic orientations. The latter group was eliminated from the data because farmers in this group had the highest scores for almost all items of the questionnaire, whether or not these concerned positive or negative aspects of entrepreneurship. Moreover, they gave contradictory answers to comparable questions. Based on future expectations and family income, it was concluded that social farmers and new growers were more successful than other farmers. According to economic theories, they also seemed to meet the "demands" of "real" entrepreneurship better than other farmers because they can be called "movers of the market,""innovators," and/or "discoverers of profit opportunities." New growers and social farmers were also distinguishable from the other groups of farmers by their personal characteristics. In general, it could be concluded that positive personal characteristics (self-criticism, leadership, creativity, perseverance, and initiative) affected agricultural entrepreneurship positively, and negative personal characteristics (love of ease and passivity) affected it negatively. Copyright 2005 International Association of Agricultural Economics.