12,645 research outputs found
Are there any nicely structured preference~profiles~nearby?
We investigate the problem of deciding whether a given preference profile is
close to having a certain nice structure, as for instance single-peaked,
single-caved, single-crossing, value-restricted, best-restricted,
worst-restricted, medium-restricted, or group-separable profiles. We measure
this distance by the number of voters or alternatives that have to be deleted
to make the profile a nicely structured one. Our results classify the problem
variants with respect to their computational complexity, and draw a clear line
between computationally tractable (polynomial-time solvable) and
computationally intractable (NP-hard) questions
Parameterized Algorithmics for Computational Social Choice: Nine Research Challenges
Computational Social Choice is an interdisciplinary research area involving
Economics, Political Science, and Social Science on the one side, and
Mathematics and Computer Science (including Artificial Intelligence and
Multiagent Systems) on the other side. Typical computational problems studied
in this field include the vulnerability of voting procedures against attacks,
or preference aggregation in multi-agent systems. Parameterized Algorithmics is
a subfield of Theoretical Computer Science seeking to exploit meaningful
problem-specific parameters in order to identify tractable special cases of in
general computationally hard problems. In this paper, we propose nine of our
favorite research challenges concerning the parameterized complexity of
problems appearing in this context
Necessary and sufficient conditions for a resolution of the social choice paradox
We present a restriction on the domain of individual preferences that is both necessary and sufficient for the existence of a social choice rule that is continuous, anonymous, and respects unanimity. The restriction is that the space of preferences be contractible. Contractibility admits a straightforward intuitive explanation, and is a generalisation of conditions such as single peakedness, value restrictedness and limited agreement, which were earlier shown to be sufficient for majority voting to be an acceptable rule. The only restriction on the number of individuals, is that it be finite and at least 2.social choice; preferences; mathematical modeling
Beyond Classification: Latent User Interests Profiling from Visual Contents Analysis
User preference profiling is an important task in modern online social
networks (OSN). With the proliferation of image-centric social platforms, such
as Pinterest, visual contents have become one of the most informative data
streams for understanding user preferences. Traditional approaches usually
treat visual content analysis as a general classification problem where one or
more labels are assigned to each image. Although such an approach simplifies
the process of image analysis, it misses the rich context and visual cues that
play an important role in people's perception of images. In this paper, we
explore the possibilities of learning a user's latent visual preferences
directly from image contents. We propose a distance metric learning method
based on Deep Convolutional Neural Networks (CNN) to directly extract
similarity information from visual contents and use the derived distance metric
to mine individual users' fine-grained visual preferences. Through our
preliminary experiments using data from 5,790 Pinterest users, we show that
even for the images within the same category, each user possesses distinct and
individually-identifiable visual preferences that are consistent over their
lifetime. Our results underscore the untapped potential of finer-grained visual
preference profiling in understanding users' preferences.Comment: 2015 IEEE 15th International Conference on Data Mining Workshop
Parametrising arbitrary galaxy morphologies: potentials and pitfalls
We demonstrate that morphological observables (e.g. steepness of the radial
light profile, ellipticity, asymmetry) are intertwined and cannot be measured
independently of each other. We present strong arguments in favour of
model-based parametrisation schemes, namely reliability assessment,
disentanglement of morphological observables, and PSF modelling. Furthermore,
we demonstrate that estimates of the concentration and Sersic index obtained
from the Zurich Structure & Morphology catalogue are in excellent agreement
with theoretical predictions. We also demonstrate that the incautious use of
the concentration index for classification purposes can cause a severe loss of
the discriminative information contained in a given data sample. Moreover, we
show that, for poorly resolved galaxies, concentration index and M_20 suffer
from strong discontinuities, i.e. similar morphologies are not necessarily
mapped to neighbouring points in the parameter space. This limits the
reliability of these parameters for classification purposes. Two-dimensional
Sersic profiles accounting for centroid and ellipticity are identified as the
currently most reliable parametrisation scheme in the regime of intermediate
signal-to-noise ratios and resolutions, where asymmetries and substructures do
not play an important role. We argue that basis functions provide good
parametrisation schemes in the regimes of high signal-to-noise ratios and
resolutions. Concerning Sersic profiles, we show that scale radii cannot be
compared directly for profiles of different Sersic indices. Furthermore, we
show that parameter spaces are typically highly nonlinear. This implies that
significant caution is required when distance-based classificaton methods are
used.Comment: 18 pages, 13 figure
Social choice and game theory: recent results with a topological approach
This chapter presents a summary of recent results obtained in game and social choice theories, and highlights the application and the development of tools in algebraic topology. The purpose is expository: no attempt is made to provide complete proofs, for which references are given, nor to review the previous work in this area, which covers a significant subset of the economic literature. The aim is to provide an oriented guide to recent results, through economic examples with geometric interpretations, and to indicate possible fruitful avenues of research.social choice; game theory; algebraic topology; topological; pareto condition; preferences; Nash equilibrium; transversality
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