The categorical approach to social choice theory

A number of different problems in social choice theory are given a common treatment in the framework of category theory. A social choice function is a map μ from a set Hom(A, PX) of profiles - in applications functions from a set A of agents to the set PX of linear orders on a set X of alternatives - to a set GPX the nature of which depends on the application. The main theorem established is applied to social welfare functions and strategy-proof voting schemes.     

Pareto optimality,anonymity, and strategy-proofness in location problems

Generalized location problems withn agents are considered, who each report a point inm-dimensional Euclidean space. A solution assigns a compromise point to thesen points, and the individual utilities for this compromise point are equal to the negatives of the Euclidean distances to the individual positions. Form = 2 andn odd, it is shown that a solution is Pareto optimal, anonymous, and strategy-proof if, and only if, it is obtained by taking the coordinatewise median with respect to a pair of orthogonal axes. Further, for all other situations withm2, such a solution does not exist. A few results concerning other solution properties, as well as different utility functions, are discussed.Supported by a grant from the Cooperation Centre Tilburg and Eindhoven University.     

Generalized median solutions,strategy-proofness and strictly convex norms

Generalized location problems withn agents are considered, who each report a point inm-dimensional Euclidean space. A solution assigns a compromise point to thesen points, and the individual utilities for this compromise point are equal to the negatives of the distances to the individual positions. These distances are measured by a given strictly convex norm, common to all agents. Form=2, it is shown that if a Pareto optimal, strategy-proof and anonymous solution exists, thenn must be odd, and the solution is obtained by taking the median coordinatewise, where the coordinates refer to a basis that is orthogonal with respect to the given norm. Furthermore, in that case (m=2) such a solution always exists. Form > 2, existence of a solution depends on the norm.Supported by a grant from the Cooperation Centre Tilburg and Eindhoven University.     

阿罗不可能性定理的几个等价形式

在这篇短中。给出了关于社会福利函数F的防止策略性操纵的概念,并且证明了如果备选对象至少有三个。则下面结论是相互等价的：(1)F满足Pareto与IIA性质;(2)F满足Pareto与RID性质;(3)F是独裁的;(4)F是满的、正向响应的;(5)F是防止策略操纵的且F是满的。     

A core of voting games with improved foresight

This paper considers voting situations in which the vote takes place iteratively. If a coalition replaces the status quo a with a contestant b, then b becomes the new status quo, and the vote goes on until a candidate is reached that no winning coalition is willing to replace. It is well known that the core, that is, the set of undominated alternatives, may be empty. To alleviate this problem, Rubinstein [Rubinstein, A., 1980. Stability of decision systems under majority rule. Journal of Economic Theory 23, 150–159] assumes that voters look forward one vote before deciding to replace an alternative by a new one. They will not do so if the new status quo is going to be replaced by a third that is less interesting than the first. The stability set, that is, the set of undominated alternatives under this behavior, is always non-empty when preferences are strict. However, this is not necessarily the case when voters’ indifference is allowed. Le Breton and Salles [Le Breton, M., Salles, M., 1990. The stability set of voting games: Classification and generecity results. International Journal of Game Theory 19, 111–127], Li [Li, S., 1993. Stability of voting games. Social Choice and Welfare 10, 51–56] and Martin [Martin, M., 1998. Quota games and stability set of order d. Economic Letters 59, 145–151] extend the sophistication of the voters by having them look d votes forward along the iterative process. For d sufficiently large, the resulting set of undominated alternatives is always non-empty even if indifference is allowed. We show that it may be unduly large. Next, by assuming that other voters along a chain of votes are also rational, that is, they also look forward to make sure that the votes taking place later on will not lead to a worst issue for them, we are able to reduce the size of this set while insuring its non-emptiness. Finally, we show that a vote with sufficient foresight satisfies a no-regret property, contrarily to the classical core and the stability set.     

The Shapley–Shubik index for simple games with multiple alternatives

When analyzing mathematically decision mechanisms ruled by voting it is sometimes convenient to include abstention as a possible alternative for the voters. In classical simple games, abstention, if considered, is formally equivalent to voting against the proposal. Simple games with alternatives are useful to study voting systems where abstention does not favour any of the options. In this work, we axiomatically characterize the Shapley–Shubik index for simple games with alternatives and apply it to an example taken from real life. This work has been partially supported by Grant MTM 2006–06064 of the Education and Science Spanish Ministry and the European Regional Development Fund, and Grant SGR 2005–00651 of the Catalonia Government.     

Consensus reaching in committees

In this paper, we apply a consensus model to decision-making in committees that have to choose one or more alternatives from a set of alternatives. The model does not use a voting rule nor a set of winning coalitions. Every decision maker evaluates each alternative with respect to given criteria. The criteria may be of unequal importance to a decision maker. Decision makers may be advised by a chairman to adjust their preferences, i.e., to change their evaluation of some alternative(s) or/and the importance of the criteria, in order to obtain a better consensus. The consensus result should satisfy constraints concerning the consensus degree and the majority degree. A simple example is presented.     

Optimal bounds for the no-show paradox via SAT solving

One of the most important desirable properties in social choice theory is Condorcet-consistency, which requires that a voting rule should return an alternative that is preferred to any other alternative by some majority of voters. Another desirable property is participation, which requires that no voter should be worse off by joining an electorate. A seminal result by Moulin (1988) has shown that Condorcet-consistency and participation are incompatible whenever there are at least 4 alternatives and 25 voters. We leverage SAT solving to obtain an elegant human-readable proof of Moulin’s result that requires only 12 voters. Moreover, the SAT solver is able to construct a Condorcet-consistent voting rule that satisfies participation as well as a number of other desirable properties for up to 11 voters, proving the optimality of the above bound. We also obtain tight results for set-valued and probabilistic voting rules, which complement and significantly improve existing theorems.     

Random utility models with all choice probabilities expressible as ‘functions’ of the binary choice probabilities

Given the absence of non-trivial decision rules which are strategy-proof in the Gibbard-Satterthwaite sense, Peleg and Sen have suggested that one might search for decision rules under which there will be always some Nash equilibrium yielding the same outcome as would be yielded by honest voting. This paper shows that most decision rules based on pairwise comparison will fail to satisfy the requirement of Peleg and Sen if one imposes the additional condition that the relevant Nash equilibrium should consist of undominated voting strategies only (a most reasonable condition in the absence of cooperation). It is also shown that under most decision rules based on pairwise comparisons, it will not be possible either to ensure that the outcome of honest voting will be always an outcome of sophisticated voting (in Farquharson's sense) or to ensure that the outcome of honest voting will be always a core outcome.     

Association schemes related to universally optimal configurations, Kerdock codes and extremal Euclidean line-sets

H. Cohn et al. proposed an association scheme of 64 points in R¹⁴ which is conjectured to be a universally optimal code. We show that this scheme has a generalization in terms of Kerdock codes, as well as in terms of maximal collections of real mutually unbiased bases. These schemes are also related to extremal line-sets in Euclidean spaces and Barnes-Wall lattices. D. de Caen and E.R. van Dam constructed two infinite series of formally dual 3-class association schemes. We explain this formal duality by constructing two dual abelian schemes related to quaternary linear Kerdock and Preparata codes.     

Smoothness equivalence properties of univariate subdivision schemes and their projection analogues

We study the following modification of a linear subdivision scheme S: let M be a surface embedded in Euclidean space, and P a smooth projection mapping onto M. Then the P-projection analogue of S is defined as T := P ◦ S. As it turns out, the smoothness of the scheme T is always at least as high as the smoothness of the underlying scheme S or the smoothness of P minus 1, whichever is lower. To prove this we use the method of proximity as introduced by Wallner et al. (Constr Approx 24(3):289–318, 2006; Comput Aided Geom Design 22(7):593–622, 2005). While smoothness equivalence results are already available for interpolatory schemes S, this is the first result that confirms smoothness equivalence properties of arbitrary order for general non-interpolatory schemes.     

路网规划方案的模糊迭代方法及应用

路网规划评价中评价因素的权重确定是应用中的难点,采用同时确定因素权重和方案隶属度的模糊迭代方法较好解决因素权重值计算,由于决策者推荐方案中隐含的决策意图,使排序结果更为客观和合理,避免了实际工作中因素权值确定的不客观性,显著提高了决策效果.     

Individual strategy and manipulation of issues

Much of the existing literature on strategic voting assumes that the issue (i.e. the set of alternatives out of which society has to make its choice) is given. Attention is then focussed on whether any coalition of individuals will find it profitable to disrupt the sincere voting situation. In this paper, we analyse the problem of strategy in sponsoring alternatives, using Farquharson's notion of sophisticated voting. It is shown that sincere sponsoring of alternatives is unlikely to take place under a plausible assumption regarding how individuals vote once the issue is determined.     

On parallel asynchronous high-order solutions of parabolic PDEs

In achieving significant speed-up on parallel machines, a major obstacle is the overhead associated with synchronizing the concurrent processes. This paper presents high-orderparallel asynchronous schemes, which are schemes that are specifically designed to minimize the associated synchronization overhead of a parallel machine in solving parabolic PDEs. They are asynchronous in the sense that each processor is allowed to advance at its own speed. Thus, these schemes are suitable for single (or multi) user shared memory or (message passing) MIMD multiprocessors. Our approach is demonstrated for the solution of the multidimensional heat equation, of which we present a spatial second-order Parametric Asynchronous Finite-Difference (PAFD) scheme. The well-known synchronous schemes are obtained as its special cases. This is a generalization and expansion of the results in [5] and [7]. The consistency, stability and convergence of this scheme are investigated in detail. Numerical tests show that although PAFD provides the desired order of accuracy, its efficiency is inadequate when performed on each grid point.In an alternative approach that uses domain decomposition, the problem domain is divided among the processors. Each processor computes its subdomain mostly independently, while the PAFD scheme provides the solutions at the subdomains' boundaries. We use high-order finite-difference implicit scheme within each subdomain and determine the values at subdomains' boundaries by the PAFD scheme. Moreover, in order to allow larger time-step, we use remote neighbors' values rather than those of the immediate neighbors. Numerical tests show that this approach provides high efficiency and in the case which uses remote neighbors' values an almost linear speedup is achieved. Schemes similar to the PAFD can be developed for other types of equations [3].This research was supported by the fund for promotion of research at the Technion.     

Probabilistic,fuzzy and rough concepts in social choice

We discuss how intrinsic inconsistencies and negative results (concerning opinion aggregation) in social choice may be alleviated by plausible modifications of underlying assumptions and problem formulations, basically by the introduction of some impreciseness of a probabilistic, fuzzy and rough type. First, we discuss briefly probabilistic voting, and the use of fuzzy preference relations and fuzzy majorities. Then, in the main part, we proceed to the use of Pawlak's rough sets theory in the analysis of crucial properties of voting schemes. In this framework we also discuss the concept of a distance between two voting schemes. Finally, we further explore difficult issues of how diverse types of impreciseness can be combined, and we consider in particular the combination of roughness with randomness and fuzziness in the context of spatial voting games.     

考虑决策者心理行为的直觉语言多属性决策方法

针对应用直觉语言集来表达决策信息的语言多属性决策问题,在考虑决策者有限理性的心理行为基础上,提出一种决策方法。该方法通过比较每个属性下方案之间的得分函数和精确函数, 构建方案的收益-损失分析矩阵。在考虑决策者参照依赖和损失规避心理行为基础上,计算每个方案相对于其它方案在每个属性下的收益-损失值优先度;在此基础上,计算备选方案的综合优先度, 并根据其大小对方案进行排序择优。最后通过一个算例验证所提出方法的有效性和合理性。     

An improved method for ranking alternatives in multiple criteria decision analysis

Scoring rules are an important disputable subject in data envelopment analysis (DEA). Various organizations use voting systems whose main object is to rank alternatives. In these methods, the ranks of alternatives are obtained by their associated weights. The method for determining the ranks of alternatives by their weights is an important issue. This problem has been the subject at hand of some authors. We suggest a three-stage method for the ranking of alternatives. In the first stage, the rank position of each alternative is computed based on the best and worst weights in the optimistic and pessimistic cases, respectively. The vector of weights obtained in the first stage is not a singleton. Hence, to deal with this problem, a secondary goal is used in the second stage. In the third stage of our method, the ranks of the alternatives approach the optimistic or pessimistic case. It is mentionable that the model proposed in the third stage is a multi-criteria decision making (MCDM) model and there are several methods for solving it; we use the weighted sum method in this paper. The model is solved by mixed integer programming. Also, we obtain an interval for the rank of each alternative. We present two models on the basis of the average of ranks in the optimistic and pessimistic cases. The aim of these models is to compute the rank by common weights.     

Geometry of decision making and the vector space formulation of the analytic hierarchy process

We extend the conventional Analytic Hierarchy Process (AHP) to an Euclidean vector space and develop formulations for aggregation of the alternative preferences with the criteria preferences. Relative priorities obtained from such a formulation are almost identical with the ones obtained using conventional AHP. Each decision is represented by a preference vector indicating the orientation of the decision maker's mind in the decision space spanned by the decision alternatives. This adds a geometric meaning to the decision making processes. We utilise the measure of similarity between any two decision makers and apply it for analysing decisions in a homogeneous group. We propose an aggregation scheme for calculating the group preference from individual preferences using a simple vector addition procedure that satisfies Pareto optimality condition. The results agree very well with the ones of conventional AHP.     

Assessing research effectiveness: a comparison of alternative nonparametric models

In this paper, we examine three alternative a posteriori weighting schemes with variable, common and restricted weights in order to assess research productivity by means of two seemingly similar nonparametric models: the Benefit-of-the-doubt and the Kao and Hung (2003) model. Our empirical results, based on different types of faculty members’ publications, show that there is more variability in the estimated effectiveness scores among alternative weighting schemes within each model rather than between models for any particular weighting scheme. In addition, we also found that the effectiveness scores from the BoD model are greater than or equal to those from the K&H model for the variable- and the restricted-weights schemes while there is no clear pattern between the BoD and the K&H effectiveness scores from the common-weights scheme.     

承诺方案的研究

承诺方案是一种重要而有用的密码学基本协议,它在密码学领域中的零知识证明、安全多方计算协议、电子货币、电子选举等众多密码学协议的构造中起着十分重要的作用.我们介绍了承诺方案的应用背景、定义、分类、构造以及它在密码学领域中所起的重要作用.同时,对目前密码学领域中关于承诺方案的研究热点也进行了阐述.