Enhanced sharing analysis techniques: a comprehensive evaluation

Sharing, an abstract domain developed by D. Jacobs and A. Langen for the analysis of logic programs, derives useful aliasing information. It is well-known that a commonly used core of techniques, such as the integration of Sharing with freeness and linearity information, can significantly improve the precision of the analysis. However, a number of other proposals for refined domain combinations have been circulating for years. One feature that is common to these proposals is that they do not seem to have undergone a thorough experimental evaluation even with respect to the expected precision gains. In this paper we experimentally evaluate: helping Sharing with the definitely ground variables found using Pos, the domain of positive Boolean formulas; the incorporation of explicit structural information; a full implementation of the reduced product of Sharing and Pos; the issue of reordering the bindings in the computation of the abstract mgu; an original proposal for the addition of a new mode recording the set of variables that are deemed to be ground or free; a refined way of using linearity to improve the analysis; the recovery of hidden information in the combination of Sharing with freeness information. Finally, we discuss the issue of whether tracking compoundness allows the computation of more sharing information

A correct, precise and efficient integration of set-sharing, freeness and linearity for the analysis of finite and rational tree languages

It is well known that freeness and linearity information positively interact with aliasing information, allowing both the precision and the efficiency of the sharing analysis of logic programs to be improved. In this paper, we present a novel combination of set-sharing with freeness and linearity information, which is characterized by an improved abstract unification operator. We provide a new abstraction function and prove the correctness of the analysis for both the finite tree and the rational tree cases. Moreover, we show that the same notion of redundant information as identified in Bagnara et al. (2000) and Zaffanella et al. (2002) also applies to this abstract domain combination: this allows for the implementation of an abstract unification operator running in polynomial time and achieving the same precision on all the considered observable properties

Three Optimisations for Sharing

In order to improve precision and efficiency sharing analysis should track both freeness and linearity. The abstract unification algorithms for these combined domains are suboptimal, hence there is scope for improving precision. This paper proposes three optimisations for tracing sharing in combination with freeness and linearity. A novel connection between equations and sharing abstractions is used to establish correctness of these optimisations even in the presence of rational trees. A method for pruning intermediate sharing abstractions to improve efficiency is also proposed. The optimisations are lightweight and therefore some, if not all, of these optimisations will be of interest to the implementor.Comment: To appear in Theiry and Practice of Logic Programmin

Incentives under collusion in a two-agent hidden-action model of a financial enterprize

This study analyzes collusion in an enterprize in which concerns about hedging cannot be ignored. In our two-agent single-task hidden-action model, where all the parties involved have exponential utility functions and the principal owning normally distributed observable and verifiable returns is restricted to o®er linear contracts, agents may exploit all feasible collusion opportunities via enforceable side contracts. Hence in general, an optimal incentive compatible and individually rational contract is not necessarily immune to collusion. We demonstrate that collusion may be ignored when making the agents work with the highest effort profile is profitable for the principal and either of the following holds: (1) mean of the return is only a®ected by the first agent's effort level, whereas variance of that is only affected by the second agent's, (2) mean is increasing and variance is decreasing separately in effort levels of both of them. On the other hand, for situations in which any of these assumptions are violated, numerical examples, showing that collusion may make the principal strictly worse off, are provided. For the justification of linear contracts as was done in the model of Holmstrom and Milgrom (1987) we consider a variant of its generalization given by Sung (1995), into which collusion possibilities are incorporated. In that continuous-time repeated agency problem including collusion, we prove the optimality of linear contracts

Local load sharing fiber bundles with a lower cutoff of strength disorder

We study the failure properties of fiber bundles with a finite lower cutoff of the strength disorder varying the range of interaction between the limiting cases of completely global and completely local load sharing. Computer simulations revealed that at any range of load redistribution there exists a critical cutoff strength where the macroscopic response of the bundle becomes perfectly brittle, i.e. linearly elastic behavior is obtained up to global failure, which occurs catastrophically after the breaking of a small number of fibers. As an extension of recent mean field studies [Phys. Rev. Lett. 95, 125501 (2005)], we demonstrate that approaching the critical cutoff, the size distribution of bursts of breaking fibers shows a crossover to a universal power law form with an exponent 3/2 independent of the range of interaction.Comment: 4 pages, 4 figure

Muon Spectrometer Phase-I Upgrade for the ATLAS Experiment: the New Small Wheel project

The instantaneous luminosity of the Large Hadron Collider at CERN will be increased by up to a factor of five to seven with respect to the design value. To maintain an excellent detection and background rejection capability in the forward region of the ATLAS detector, part of the muon detection system will be upgraded during LHC shutdown periods with the replacement of part of the present first station in the forward regions with the so-called New Small Wheels (NSWs). The NSWs will have a diameter of approximately 10 m and will be made of two detector technologies: Micromegas and small-strip Thin Gap Chambers (sTGC). The physics motivation for this significant upgrade to the ATLAS detector will be presented. The design choices made to address the physics needs will be discussed. Finally, the status of the production of the detector modules will be presented.Comment: 10 pages, presented at CIPANP 201