Constraint Logic Programming for Natural Language Processing

This paper proposes an evaluation of the adequacy of the constraint logic programming paradigm for natural language processing. Theoretical aspects of this question have been discussed in several works. We adopt here a pragmatic point of view and our argumentation relies on concrete solutions. Using actual contraints (in the CLP sense) is neither easy nor direct. However, CLP can improve parsing techniques in several aspects such as concision, control, efficiency or direct representation of linguistic formalism. This discussion is illustrated by several examples and the presentation of an HPSG parser.Comment: 15 pages, uuencoded and compressed postscript to appear in Proceedings of the 5th Int. Workshop on Natural Language Understanding and Logic Programming. Lisbon, Portugal. 199

An analysis and implementation of linear derivation strategies

This study examines the efficacy of six linear derivation strategies: (i) s-linear resolution, (ii) the ME procedure; (iii) t-linear resolution, (iv) SL -resolution, (v) the GC procedure, and (vi) SLM. The analysis is focused on the different restrictions and operations employed in each derivation strategy. The selection function, restrictive ancestor resolution, compulsory ancestor resolution on literals having atoms which are or become identical, compulsory merging operations, reuse of truncated literals, spreading of FALSE literals, no-tautologies resection, no two non-B-literals having identical atoms restriction, and the use of semantic information to trim irrelevant derivations from the search tree are the major features found In these six derivation strategies. Detecting loops and minimizing irrelevant derivations are the identified weak points of SLM. Two variations of SLM are suggested to rectify these problems. The ME procedure, SL-resolution, the GC procedure, SLM and one of the suggested variations of SLM were implemented using the Arity/Prolog compiler to produce the ME -TP, SL-TP, GC-TP, SLM-TP and SLM5-TP theorem provers respectively. In addition to the original features of each derivation strategy, the following search strategies were included in the implementations : the modified consecutively bounded depth-first search unit preference strategy, set of support strategy, pure literal elimination, tautologous clause elimination, selection function based on the computed weight of a literal, and a match check. The extension operation used by each theorem prover was extended to include subsumed unit extension and paramodulation. The performance of each theorem prover was determined. Experimental results were obtained using twenty four selected problems. The performance was measured in terms of the memory use and the execution time. A comparison of results between the five theorem provers using the, ME-TP as the basis was done. The results show that none of the theorem provers, consistently perform better than the others. Two of the selected problems were not proved by SL-TP and one problem was not proved by SLM-TP due to memory problems. The ME-TP, GC-TP and SLM5-TP proved all the selected problems. In some problems, the ME-TP and GC-TP performed better than SLM5-TP. However, the ME-TP and GC-TP had difficulties in some problems in which SLM5-TP performed well

Natural conjugate priors for the instrumental variables regression model applied to the Angrist-Krueger data

We propose a natural conjugate prior for the instrumentalvariables regression model. The prior is a natural conjugate onesince the marginal prior and posterior of the structural parameterhave the same functional expressions which directly reveal theupdate from prior to posterior. The Jeffreys prior results from aspecific setting of the prior parameters and results in a marginalposterior of the structural parameter that has an identicalfunctional form as the sampling density of the limited informationmaximum likelihood estimator. We construct informative priors forthe Angrist-Krueger (1991) data and show that the marginalposterior of the return on education in the US coincides with themarginal posterior from the Southern region when we use theJeffreys prior. This result occurs since the instruments are thestrongest in the Southern region and the posterior using theJeffreys prior, identical to maximum likelihood, focusses on thestrongest available instruments. We construct informative priorsfor the other regions that make their posteriors of the return oneducation similar to that of the US and the Southern region. Thesepriors show the amount of prior information needed to obtaincomparable results for all regions.

Why Money Trickles Up - Wealth & Income Distributions

This paper combines ideas from classical economics and modern finance with the general Lotka-Volterra models of Levy & Solomon to provide straightforward explanations of wealth and income distributions. Using a simple and realistic economic formulation, the distributions of both wealth and income are fully explained. Both the power tail and the log-normal like body are fully captured. It is of note that the full distribution, including the power law tail, is created via the use of absolutely identical agents. It is further demonstrated that a simple scheme of compulsory saving could eliminate poverty at little cost to the taxpayer.Comment: 45 pages of text, 36 figure

The management of de-cumulation risks in a defined contribution environment

The aim of the paper is to lay the theoretical foundations for the construction of a flexible tool that can be used by pensioners to find optimal investment and consumption choices in the distribution phase of a defined contribution pension scheme. The investment/consumption plan is adopted until the time of compulsory annuitization, taking into account the possibility of earlier death. The effect of the bequest motive and the desire to buy a higher annuity than the one purchasable at retirement are included in the objective function. The mathematical tools provided by dynamic programming techniques are applied to find closed form solutions: numer-ical examples are also presented. In the model, the trade-off between the different desires of the individual regarding consumption and final annuity can be dealt with by choosing appropriate weights for these factors in the setting of the problem. Conclusions are twofold. Firstly, we find that there is a natural time-varying target for the size of the fund, which acts as a sort of safety level for the needs of the pensioner. Secondly, the personal preferences of the pensioner can be translated into optimal choices, which in turn affect the distribution of the consumption path and of the final annuity

A Library for Pattern-based Sparse Matrix Vector Multiply

Pattern-based Representation (PBR) is a novel approach to improving the performance of Sparse Matrix-Vector Multiply (SMVM) numerical kernels. Motivated by our observation that many matrices can be divided into blocks that share a small number of distinct patterns, we generate custom multiplication kernels for frequently recurring block patterns. The resulting reduction in index overhead significantly reduces memory bandwidth requirements and improves performance. Unlike existing methods, PBR requires neither detection of dense blocks nor zero filling, making it particularly advantageous for matrices that lack dense nonzero concentrations. SMVM kernels for PBR can benefit from explicit prefetching and vectorization, and are amenable to parallelization. The analysis and format conversion to PBR is implemented as a library, making it suitable for applications that generate matrices dynamically at runtime. We present sequential and parallel performance results for PBR on two current multicore architectures, which show that PBR outperforms available alternatives for the matrices to which it is applicable, and that the analysis and conversion overhead is amortized in realistic application scenarios

From IRAP to CBIT: tax distortions and redistributive effects

The paper explores the differences between IRAP (the Regional Tax on Productive Activities) and CBIT (the Comprehensive Business Income Tax), which approximately corresponds to allow the deduction of labor cost from the taxable base of IRAP. By developing a DSGE model that ncorporates business taxes, like IRAP or CBIT, we find that tax distortions due to IRAP are more contractionary than those caused by the presence of CBIT. Empirically, tax revenues and redistributive effects are more carefully analyzed. We implement a microsimulation model (MSM) based on a dataset of more than 150,000 incorporated firms. We show that small incorporated firms are particularly harmed by IRAP, especially when business run a loss instead of a profit. This is due to the fact that IRAP is a business tax on value added, which does not allow for the deduction of labor cost. For this purpose, we focus on the introduction of a reform based on the CBIT principle. Our result is that CBIT is particularly costly and more able to enhance the profitability for larger enterprises. Moreover, the tax design of CBIT is more regressive compared to the IRAP including tax allowances. Consequently, an efficiency-equity trade-off between IRAP and CBIT might be emphasizedbusiness cycles, tax distortions, micro-simulations models, distributive effects, Italy.

Financing Pharmaceutical Innovation: How Much Should Poor Countries Contribute?

We use a public economics framework to consider how pharmaceuticals should be priced when at least some of the R&D incentive comes from sales revenues. We employ familiar techniques of public finance to relax some of the restrictions implied in the standard use of Ramsey pricing. In the more general model, poor countries should not necessarily cover even their own marginal costs, and the pricing structure is not related to that which would be chosen by a monopolist in a simple way. We use this framework to examine on-going debates regarding the international patent system as embodied in the WTO’s TRIPS agreement.pharmaceutical, poor countries, pricing structure, patent system