867 research outputs found
The Fixpoint-Iteration Algorithm for Parity Games
It is known that the model checking problem for the modal mu-calculus reduces
to the problem of solving a parity game and vice-versa. The latter is realised
by the Walukiewicz formulas which are satisfied by a node in a parity game iff
player 0 wins the game from this node. Thus, they define her winning region,
and any model checking algorithm for the modal mu-calculus, suitably
specialised to the Walukiewicz formulas, yields an algorithm for solving parity
games. In this paper we study the effect of employing the most straight-forward
mu-calculus model checking algorithm: fixpoint iteration. This is also one of
the few algorithms, if not the only one, that were not originally devised for
parity game solving already. While an empirical study quickly shows that this
does not yield an algorithm that works well in practice, it is interesting from
a theoretical point for two reasons: first, it is exponential on virtually all
families of games that were designed as lower bounds for very particular
algorithms suggesting that fixpoint iteration is connected to all those.
Second, fixpoint iteration does not compute positional winning strategies. Note
that the Walukiewicz formulas only define winning regions; some additional work
is needed in order to make this algorithm compute winning strategies. We show
that these are particular exponential-space strategies which we call
eventually-positional, and we show how positional ones can be extracted from
them.Comment: In Proceedings GandALF 2014, arXiv:1408.556
A Canonical Model Construction for Iteration-Free PDL with Intersection
We study the axiomatisability of the iteration-free fragment of Propositional
Dynamic Logic with Intersection and Tests. The combination of program
composition, intersection and tests makes its proof-theory rather difficult. We
develop a normal form for formulae which minimises the interaction between
these operators, as well as a refined canonical model construction. From these
we derive an axiom system and a proof of its strong completeness.Comment: In Proceedings GandALF 2016, arXiv:1609.0364
Model Checking Timed Recursive CTL
We introduce Timed Recursive CTL, a merger of two extensions of the well-known branching-time logic CTL: Timed CTL is interpreted over real-time systems like timed automata; Recursive CTL introduces a powerful recursion operator which takes the expressiveness of this logic CTL well beyond that of regular properties. The result is an expressive logic for real-time properties. We show that its model checking problem is decidable over timed automata, namely 2-EXPTIME-complete
Temporal Logic with Recursion
We introduce extensions of the standard temporal logics CTL and LTL with a recursion operator that takes propositional arguments. Unlike other proposals for modal fixpoint logics of high expressive power, we obtain logics that retain some of the appealing pragmatic advantages of CTL and LTL, yet have expressive power beyond that of the modal ?-calculus or MSO. We advocate these logics by showing how the recursion operator can be used to express interesting non-regular properties. We also study decidability and complexity issues of the standard decision problems
Generative Adversarial Networks for Bitcoin Data Augmentation
In Bitcoin entity classification, results are strongly conditioned by the
ground-truth dataset, especially when applying supervised machine learning
approaches. However, these ground-truth datasets are frequently affected by
significant class imbalance as generally they contain much more information
regarding legal services (Exchange, Gambling), than regarding services that may
be related to illicit activities (Mixer, Service). Class imbalance increases
the complexity of applying machine learning techniques and reduces the quality
of classification results, especially for underrepresented, but critical
classes.
In this paper, we propose to address this problem by using Generative
Adversarial Networks (GANs) for Bitcoin data augmentation as GANs recently have
shown promising results in the domain of image classification. However, there
is no "one-fits-all" GAN solution that works for every scenario. In fact,
setting GAN training parameters is non-trivial and heavily affects the quality
of the generated synthetic data. We therefore evaluate how GAN parameters such
as the optimization function, the size of the dataset and the chosen batch size
affect GAN implementation for one underrepresented entity class (Mining Pool)
and demonstrate how a "good" GAN configuration can be obtained that achieves
high similarity between synthetically generated and real Bitcoin address data.
To the best of our knowledge, this is the first study presenting GANs as a
valid tool for generating synthetic address data for data augmentation in
Bitcoin entity classification.Comment: 8 pages, 5 figures, 4 table
LAI based trees selection for mid latitude urban developments: A microclimatic study in Cairo, Egypt
To study the leaf area index, LAI, based thermal performance in distinguishing trees for Cairo's urban developments, ENVI-met plants database was used as platform for a foliage modeling parameter, the leaf area density, LAD. Two Egyptian trees: Ficus elastica. and Peltophorum pterocarpum were simulated in 2 urban sites with one having no trees, whilst the second is having Ficus nitida trees. Trees LAD values were calculated using flat leaves' trees LAI definition to produce maximum ground solid shadow at peak time. An empirical value of 1 for LAI is applied to numerically introduce LAD values for ENVI-met.
Basically, different meteorological records showed improvements for pedestrian comfort and ambient microclimate of the building using E elastica. About 40-50% interception of direct radiation, reductions in surfaces' fluxes around trees and in radiant temperature T-mrt in comparison to base cases gave preferability to E elastica. The lack of soil water prevented evapotranspiration to take place effectively and the reduced wind speeds concluded negligible air temperature differences from both base cases except slightly appeared with the F elastica. Results show that a flat leaves tree if does not validate LAI of 1, the ground shading would not fulfill about 50% direct radiation interception and this value can be used as a reference for urban trees selection.
Further simulations were held to investigate LAI value of maximum direct radiation interception.
Performing additional simulations, F elastica of LAI of 3 intercepted almost 84% of direct radiation and revealed implications about urban trees in practice and its actual LAI. (C) 2009 Elsevier Ltd. All rights reserved
The Tail-Recursive Fragment of Timed Recursive CTL
Timed Recursive CTL (TRCTL) was recently proposed as a merger of two extensions of the well-known branching-time logic CTL: Timed CTL on one hand is interpreted over real-time systems like timed automata, and Recursive CTL (RecCTL) on the other hand obtains high expressiveness through the introduction of a recursion operator. Model checking for the resulting logic is known to be 2-EXPTIME-complete.
The aim of this paper is to investigate the possibility to obtain a fragment of lower complexity without losing too much expressive power. It is obtained by a syntactic property called "tail-recursiveness" that restricts the way that recursive formulas can be built. This restriction is known to decrease the complexity of model checking by half an exponential in the untimed setting. We show that this also works in the real-time world: model checking for the tail-recursive fragment of TRCTL is EXPSPACE-complete. The upper bound is obtained by a standard untiming construction via region graphs, and rests on the known complexity of tail-recursive fragments of higher-order modal logics. The lower bound is established by a reduction from a suitable tiling problem
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