Repetition-free longest common subsequence of random sequences

A repetition free Longest Common Subsequence (LCS) of two sequences x and y is an LCS of x and y where each symbol may appear at most once. Let R denote the length of a repetition free LCS of two sequences of n symbols each one chosen randomly, uniformly, and independently over a k-ary alphabet. We study the asymptotic, in n and k, behavior of R and establish that there are three distinct regimes, depending on the relative speed of growth of n and k. For each regime we establish the limiting behavior of R. In fact, we do more, since we actually establish tail bounds for large deviations of R from its limiting behavior. Our study is motivated by the so called exemplar model proposed by Sankoff (1999) and the related similarity measure introduced by Adi et al. (2007). A natural question that arises in this context, which as we show is related to long standing open problems in the area of probabilistic combinatorics, is to understand the asymptotic, in n and k, behavior of parameter R.Comment: 15 pages, 1 figur

Impairment losses: causes and impacts

Purpose - To analyze recognition of impairment losses in tangible and intangible assets, and their relevance to investors in companies listed in the Lisbon and Madrid Stock Exchange (2007-2011).Methodology - Quantitative analysis of a panel data sample of 80 companies listed in the Lisbon and Madrid Stock Exchange (2007-2011) was carried out. Panel data linear and non-linear regression models were estimated.Findings - We found that the amount of impairment losses showed an upward trend, and that these losses are most significant among intangibles, especially goodwill (GW). We also found that the probability of recognition of impairment losses is positively influenced by the dimension of entities and negatively by market value (p < 0.10). Portuguese export-oriented companies have a higher probability of not recognizing impairments. However, Portuguese companies with higher market values have greater probability of recognizing impairment losses, contrary to the sample as a whole, in which the relationship is negative (p < 0.10). The results also suggest that there is a smoothing effect on results because of impairments, especially in IBEX35 companies. As to the relevance of impairment losses to market value, we confirm a significant negative relationship, in line with conclusions from previous studies.Originality/value - This study contributes to the introduction of the cultural factor in this analysis, highlighting the differentiated behaviors between Portuguese and Spanish companies

Skewness in Financial Returns: Evidence from the Portuguese Stock Market (in English)

This paper addresses the issue of symmetry in financial returns. The return distributions of the major stocks traded on the Portuguese market and included in the PSI-20 Index are examined for periods from four to nine years. The results show that the symmetry of the returns is rejected against several alternative distributions. Statistically significant differences between returns below and above the mean are detected, which provides additional evidence of skewness in the return distributions. In addition, as observed in other studies, it is interesting to note that such results are similar to other low-capitalization and low-volume markets, which also exhibit asymmetric return distributions.stock markets, skewness, financial returns

From Monomials to Words to graphs

Given a finite alphabet X and an ordering on the letters, the map \sigma sends each monomial on X to the word that is the ordered product of the letter powers in the monomial. Motivated by a question on Groebner bases, we characterize ideals I in the free commutative monoid (in terms of a generating set) such that the ideal generated by \sigma(I) in the free monoid is finitely generated. Whether there exists an ordering such that is finitely generated turns out to be NP-complete. The latter problem is closely related to the recognition problem for comparability graphs.Comment: 27 pages, 2 postscript figures, uses gastex.st

Os Castelos das Ordens Militares em Portugal: estado da investigação

Esta comunicação pretende fornecer um “ponto de situação”da investigação realizada em Portugal sobre castelos das Ordens Militares desde os anos 90 até à actualidade. Apresenta-se o conjunto de fortalezas que foi objecto de pesquisas e leituras arqueológicas, arquitectónicas e/ou históricas para as várias Ordens militares fundadas em Portugal ou aqui instaladas desde o período da chamada reconquista. Destacam-se os trabalhos de vários investigadores, as dimensões das suas abordagens, os avanços realizados e as limitações que subsistem

Conventos da Ordem de Santiago em Palmela

Nesta apresentação a autora retoma a argumentação histórica e arqueológica relativa à instalação de um primeiro convento-sede da Ordem de Santiago no castelo de Palmela, nos finais do séc. XII/inícios do XIII. Avança outros indicadores da presença dos freires ao longo das duas centúrias seguintes e quando a cabeça da Ordem passa definitivamente para Palmela e se ordena a construção de um convento dentro do perímetro muralhado, fora da alcáçova. Sublinha-se, para esta fase, a escassez de dados arqueo-arquitectónicos para uma leitura consistente da casa conventual, à excepção da igreja de Santiago e de algumas dependências edificadas no tempo de D. Jorge. O último convento, hoje adaptado a pousada de turismo, é analisado através de uma planta setecentista, de alguma documentação escrita e dos resultados de uma intervenção arqueológica no pátio fronteiro à igreja