83,448 research outputs found
Abduction for (non-ominiscient) agents
Among the non-monotonic reasoning processes, abduction is one of the most important. Usually described as the process of looking florexplantions, it has been recognized as one of the most commonly used in our daily activities. Still, the traditional definitions of an abductive problem and an abductive solution mention only theories and formulas, leaving agency out of the picture. Our work proposes a study of abductive reasoning from an epistemic and dynamic perspective, making special emphasis on non-ideal agents. We begin by exploring what an abductive problema is in terms of an agent’s information, and what an abductive solution is in terms of the actions that modify it. Then we explore the different kinds of abductive problems and abductive solutions that arise when we consider agents whose information is not closed under logical consequence, and agents whose reasoning abilities are not complete
A Kolmogorov-Smirnov test for the molecular clock on Bayesian ensembles of phylogenies
Divergence date estimates are central to understand evolutionary processes
and depend, in the case of molecular phylogenies, on tests of molecular clocks.
Here we propose two non-parametric tests of strict and relaxed molecular clocks
built upon a framework that uses the empirical cumulative distribution (ECD) of
branch lengths obtained from an ensemble of Bayesian trees and well known
non-parametric (one-sample and two-sample) Kolmogorov-Smirnov (KS)
goodness-of-fit test. In the strict clock case, the method consists in using
the one-sample Kolmogorov-Smirnov (KS) test to directly test if the phylogeny
is clock-like, in other words, if it follows a Poisson law. The ECD is computed
from the discretized branch lengths and the parameter of the expected
Poisson distribution is calculated as the average branch length over the
ensemble of trees. To compensate for the auto-correlation in the ensemble of
trees and pseudo-replication we take advantage of thinning and effective sample
size, two features provided by Bayesian inference MCMC samplers. Finally, it is
observed that tree topologies with very long or very short branches lead to
Poisson mixtures and in this case we propose the use of the two-sample KS test
with samples from two continuous branch length distributions, one obtained from
an ensemble of clock-constrained trees and the other from an ensemble of
unconstrained trees. Moreover, in this second form the test can also be applied
to test for relaxed clock models. The use of a statistically equivalent
ensemble of phylogenies to obtain the branch lengths ECD, instead of one
consensus tree, yields considerable reduction of the effects of small sample
size and provides again of power.Comment: 14 pages, 9 figures, 8 tables. Minor revision, additin of a new
example and new title. Software:
https://github.com/FernandoMarcon/PKS_Test.gi
A proposal for dependent optimization in scalabale region-based coding systems
We address in this paper the problem of optimal coding in the framework of region-based video coding systems, with a special stress on content-based functionalities. We present a coding system that can provide scaled layers (using PSNR or temporal content-based scalability) such that each one has an optimal partition with optimal bit allocation among the resulting regions. This coding system is based on a dependent optimization algorithm that can provide joint optimality for a group of layers or a group of frames.Peer ReviewedPostprint (published version
MONETARY POLICY AND EXTERNAL VULNERABILITY IN BRAZIL
This paper analyses monetary policy in Brazil, investigating why interest rates were so high and volatile from 1995 to 1998. We identify in monetary policy an overreaction to external shocks, where exogenous changes in international liquidity triggered sharp movements on domestic interest rates. We also show that the Brazilian policy response to these shocks was far more intense than in Argentina and Mexico. We argue that Brazil was caught in a high interest rates trap, which culminated in a currency crisis in January 1999.
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