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With the help of a simple variational procedure it is possible to convert the partial sums of order N of many divergent series expansions f(g) = ∑∞ n=0 ang n into partial sums ∑N n=0 bng −ωn, where 0 < ω < 1 is a parameter that parametrizes the approach to the large-g limit. The latter are partial sums of a strong-coupling expansion of f(g) which converge against f(g) for g outside a certain di...

Query expansion is an effective technique in improving the retrieval performance for ad-hoc retrieval. However, query expansion can also fail, leading to a degradation of the retrieval performance. In this paper, we aim to provide a better understanding of query expansion by an empirical study on what factors can affect query expansion, and how these factors affect query expansion. We examine h...

In this paper we present a method for answering relationship questions, as posed for example in the spring of 2003 evaluation exercise of the AQUAINT program, which has funded this research. The goal of the exercise was to provide answers to questions requesting an account of the relationship between two or more entities. No restriction on the format of the answer was imposed, except that it sh...

Based on a relatively large subset representing one third of the MEDLINE collection, this paper evaluates ten different IR models (probabilistic, language model and vector-space approaches) using three different stemmers. The impact that manually assigned descriptors (MeSH headings) have on retrieval effectiveness is also evaluated. Finally, we propose both a new general blind-query expansion a...

We develop a simple and e cient algorithm to compute Riemann-Roch spaces of divisors in general algebraic function elds which does not use the Brill-Noether method of adjoints nor any series expansions. The basic idea also leads to an elementary proof of the Riemann-Roch theorem. We describe the connection to the geometry of numbers of algebraic function elds and develop a notion and algorithm ...

We consider the problem of deciding whether a given rational function has a power series expansion with all its coefficients positive. Introducing an elementary transformation that preserves such positivity we are able to provide an elementary proof for the positivity of Szegö’s function 1 (1− x)(1− y)+ (1− y)(1− z)+ (1− z)(1− x) which has been at the historical root of this subject starting wi...

Let G be a subgraph-closed graph class with bounded maximum degree. We show that if G has balanced separators whose size is smaller than linear by a polynomial factor, then G has subexponential expansion. This gives a partial converse to a result of Nešetřil and Ossona de Mendez. As an intermediate step, the proof uses a new kind of graph decompositions. The concept of graph classes with bounde...

In 1987 Kalkbrenner and Stifter tested Collins' QE algorithm on various collision problems. In this paper we report the test results of applying Hong's improved QE algorithm on the same set of problems. The tests show that the improved QE algorithm gives signiicant speedups, ranging from 30 times to at least 7000 times.

Using a simple transfer matrix approach we have derived very long series expansions for the perimeter generating function of three-choice polygons. We find that all the terms in the generating function can be reproduced from a linear Fuchsian differential equation of order 8. We perform an analysis of the properties of the differential equation.