1,721,080 research outputs found
Smart Choices and the Selection Monad
Get PDFDescribing systems in terms of choices and their resulting costs and rewards
offers the promise of freeing algorithm designers and programmers from
specifying how those choices should be made; in implementations, the choices
can be realized by optimization techniques and, increasingly, by
machine-learning methods. We study this approach from a programming-language
perspective. We define two small languages that support decision-making
abstractions: one with choices and rewards, and the other additionally with
probabilities. We give both operational and denotational semantics.
In the case of the second language we consider three denotational semantics,
with varying degrees of correlation between possible program values and
expected rewards. The operational semantics combine the usual semantics of
standard constructs with optimization over spaces of possible execution
strategies. The denotational semantics, which are compositional, rely on the
selection monad, to handle choice, augmented with an auxiliary monad to handle
other effects, such as rewards or probability.
We establish adequacy theorems that the two semantics coincide in all cases.
We also prove full abstraction at base types, with varying notions of
observation in the probabilistic case corresponding to the various degrees of
correlation. We present axioms for choice combined with rewards and
probability, establishing completeness at base types for the case of rewards
without probability
Final Semantics for untyped lambda-calculus
No full textProof principles for reasoning about various semantics of untyped λ-calculus are discussed. The semantics are determined operationally by fixing a particular reduction strategy on λ-terms and a suitable set of values, and by taking the corresponding observational equivalence on terms. These principles arise naturally as co-induction principles, when the observational equivalences are shown to be induced by the unique mapping into a final F-coalgebra, for a suitable functor F. This is achieved either by induction on computation steps or exploiting the properties of some, computationally adequate, inverse limit denotational model. The final F-coalgebras cannot be given, in general, the structure of a “denotational” λ-model. Nevertheless the “final semantics” can count as compositional in that it induces a congruence. We utilize the intuitive categorical setting of hypersets and functions. The importance of the principles introduced in this paper lies in the fact that they often allow to factorize the complexity of proofs (of observational equivalence) by “straight” induction on computation steps, which are usually lengthy and error-prone
On the Computational Power of Brane Calculi
No full textBrane calculi are a family of biologically inspired process
calculi proposed in [3] for modeling the interactions of dynamically nested
membranes.
In [3] a basic calculus for membranes interactions – called Phago/Exo/Pino
– is proposed, whose primitives are inspired by endocytosis and exocytosis.
An alternative basic calculus – called Mate/Bud/Drip and inspired
by membrane fusion and fission – is also outlined and shown to be encodable
in Phago/Exo/Pino in [3].
In this paper we investigate and compare the expressiveness of such two
calculi w.r.t. their ability to act as computational devices.
We show that (a fragment of) the Phago/Exo/Pino calculus is Turing
powerful, by providing an encoding of Random Access Machines.
On the other hand, we show the impossibility to define a “faithful” encoding
of Random Access Machines in the Mate/Bud/Drip calculus, by
providing a proof of the decidability of the existence of a divergent computation
in Mate/Bud/Drip
HMM-based Trust Model
No full textProbabilistic trust has been adopted as an approach to taking security sensitive decisions in modern global computing environments. Existing probabilistic trust frameworks either assume fixed behaviour for the principals or incorporate the notion of 'decay' as an ad hoc approach to cope with their dynamic behaviour. Using Hidden Markov Models (HMMs) for both modelling and approximating the behaviours of principals, we introduce the HMM-based trust model as a new approach to evaluating trust in systems exhibiting dynamic behaviour. This model avoids the fixed behaviour assumption which is considered the major limitation of existing Beta trust model. We show the consistency of the HMM-based trust model and contrast it against the well known Beta trust model with the decay principle in terms of the estimation precision
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Free complete Wasserstein algebras
Get PDFWe present an algebraic account of the Wasserstein distances Wp on complete metric spaces, for p ≥ 1. This is part of a program of a quantitative algebraic theory of effects in programming languages. In particular, we give axioms, parametric in p, for algebras over metric spaces equipped with probabilistic choice operations. The axioms say that the operations form a barycentric algebra and that the metric satisfies a property typical of the Wasserstein distance Wp. We show that the free complete such algebra over a complete metric space is that of the Radon probability measures with finite moments of order p, equipped with the Wasserstein distance as metric and with the usual binary convex sums as operations
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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