13,328 research outputs found
Improved classification for compositional data using the -transformation
In compositional data analysis an observation is a vector containing
non-negative values, only the relative sizes of which are considered to be of
interest. Without loss of generality, a compositional vector can be taken to be
a vector of proportions that sum to one. Data of this type arise in many areas
including geology, archaeology, biology, economics and political science. In
this paper we investigate methods for classification of compositional data. Our
approach centres on the idea of using the -transformation to transform
the data and then to classify the transformed data via regularised discriminant
analysis and the k-nearest neighbours algorithm. Using the
-transformation generalises two rival approaches in compositional data
analysis, one (when ) that treats the data as though they were
Euclidean, ignoring the compositional constraint, and another (when )
that employs Aitchison's centred log-ratio transformation. A numerical study
with several real datasets shows that whether using or
gives better classification performance depends on the dataset, and moreover
that using an intermediate value of can sometimes give better
performance than using either 1 or 0.Comment: This is a 17-page preprint and has been accepted for publication at
the Journal of Classificatio
Universal, Unsupervised (Rule-Based), Uncovered Sentiment Analysis
We present a novel unsupervised approach for multilingual sentiment analysis
driven by compositional syntax-based rules. On the one hand, we exploit some of
the main advantages of unsupervised algorithms: (1) the interpretability of
their output, in contrast with most supervised models, which behave as a black
box and (2) their robustness across different corpora and domains. On the other
hand, by introducing the concept of compositional operations and exploiting
syntactic information in the form of universal dependencies, we tackle one of
their main drawbacks: their rigidity on data that are structured differently
depending on the language concerned. Experiments show an improvement both over
existing unsupervised methods, and over state-of-the-art supervised models when
evaluating outside their corpus of origin. Experiments also show how the same
compositional operations can be shared across languages. The system is
available at http://www.grupolys.org/software/UUUSA/Comment: 19 pages, 5 Tables, 6 Figures. This is the authors version of a work
that was accepted for publication in Knowledge-Based System
Feature-Guided Black-Box Safety Testing of Deep Neural Networks
Despite the improved accuracy of deep neural networks, the discovery of
adversarial examples has raised serious safety concerns. Most existing
approaches for crafting adversarial examples necessitate some knowledge
(architecture, parameters, etc.) of the network at hand. In this paper, we
focus on image classifiers and propose a feature-guided black-box approach to
test the safety of deep neural networks that requires no such knowledge. Our
algorithm employs object detection techniques such as SIFT (Scale Invariant
Feature Transform) to extract features from an image. These features are
converted into a mutable saliency distribution, where high probability is
assigned to pixels that affect the composition of the image with respect to the
human visual system. We formulate the crafting of adversarial examples as a
two-player turn-based stochastic game, where the first player's objective is to
minimise the distance to an adversarial example by manipulating the features,
and the second player can be cooperative, adversarial, or random. We show that,
theoretically, the two-player game can con- verge to the optimal strategy, and
that the optimal strategy represents a globally minimal adversarial image. For
Lipschitz networks, we also identify conditions that provide safety guarantees
that no adversarial examples exist. Using Monte Carlo tree search we gradually
explore the game state space to search for adversarial examples. Our
experiments show that, despite the black-box setting, manipulations guided by a
perception-based saliency distribution are competitive with state-of-the-art
methods that rely on white-box saliency matrices or sophisticated optimization
procedures. Finally, we show how our method can be used to evaluate robustness
of neural networks in safety-critical applications such as traffic sign
recognition in self-driving cars.Comment: 35 pages, 5 tables, 23 figure
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