6,171 research outputs found
A Polyhedral Homotopy Algorithm For Real Zeros
We design a homotopy continuation algorithm, that is based on numerically
tracking Viro's patchworking method, for finding real zeros of sparse
polynomial systems. The algorithm is targeted for polynomial systems with
coefficients satisfying certain concavity conditions. It operates entirely over
the real numbers and tracks the optimal number of solution paths. In more
technical terms; we design an algorithm that correctly counts and finds the
real zeros of polynomial systems that are located in the unbounded components
of the complement of the underlying A-discriminant amoeba.Comment: some cosmetic changes are done and a couple of typos are fixed to
improve readability, mathematical contents remain unchange
Snapping Graph Drawings to the Grid Optimally
In geographic information systems and in the production of digital maps for
small devices with restricted computational resources one often wants to round
coordinates to a rougher grid. This removes unnecessary detail and reduces
space consumption as well as computation time. This process is called snapping
to the grid and has been investigated thoroughly from a computational-geometry
perspective. In this paper we investigate the same problem for given drawings
of planar graphs under the restriction that their combinatorial embedding must
be kept and edges are drawn straight-line. We show that the problem is NP-hard
for several objectives and provide an integer linear programming formulation.
Given a plane graph G and a positive integer w, our ILP can also be used to
draw G straight-line on a grid of width w and minimum height (if possible).Comment: Appears in the Proceedings of the 24th International Symposium on
Graph Drawing and Network Visualization (GD 2016
Radio-quiet and radio-loud pulsars: similar in Gamma-rays but different in X-rays
We present new Chandra and XMM-Newton observations of a sample of eight
radio-quiet Gamma-ray pulsars detected by the Fermi Large Area Telescope. For
all eight pulsars we identify the X-ray counterpart, based on the X-ray source
localization and the best position obtained from Gamma-ray pulsar timing. For
PSR J2030+4415 we found evidence for an about 10 arcsec-long pulsar wind
nebula. Our new results consolidate the work from Marelli et al. 2011 and
confirm that, on average, the Gamma-ray--to--X-ray flux ratios (Fgamma/Fx) of
radio-quiet pulsars are higher than for the radio-loud ones. Furthermore, while
the Fgamma/Fx distribution features a single peak for the radio-quiet pulsars,
the distribution is more dispersed for the radio-loud ones, possibly showing
two peaks. We discuss possible implications of these different distributions
based on current models for pulsar X-ray emission.Comment: Accepted for publication in The Astrophysical Journal; 12 pages, 3
figures, 2 table
The ecological approach to multimodal system design
Following the ecological approach to visual perception, this paper presents a framework that emphasizes the role of vision on referring actions. In particular, affordances are utilized to explain gestures variability in a multimodal human-computer interaction. Such a proposal is consistent with empirical findings obtained in different simulation studies showing how referring gestures are determined by the mutuality of information coming from the target and the set of movements available to the speaker. A prototype that follows anthropomorphic perceptual principles to analyze gestures has been developed and tested in preliminary computational validations
Sea ice working group (SIP)
The sea ice is a crucial component of
the polar climate system, and has
an impact on albedo, heat and gas ex-
change, primary productivity and car-
bon export, atmospheric and ocean
circulation, freshwater budget, ocean
stratification, and deep water mass for-
mation. It is therefore critical that it is
correctly specified as a forcing or pre-
dicted as a feedback in modeling stud-
ies
Learning Variational Models with Unrolling and Bilevel Optimization
In this paper we consider the problem of learning variational models in the
context of supervised learning via risk minimization. Our goal is to provide a
deeper understanding of the two approaches of learning of variational models
via bilevel optimization and via algorithm unrolling. The former considers the
variational model as a lower level optimization problem below the risk
minimization problem, while the latter replaces the lower level optimization
problem by an algorithm that solves said problem approximately. Both approaches
are used in practice, but unrolling is much simpler from a computational point
of view. To analyze and compare the two approaches, we consider a simple toy
model, and compute all risks and the respective estimators explicitly. We show
that unrolling can be better than the bilevel optimization approach, but also
that the performance of unrolling can depend significantly on further
parameters, sometimes in unexpected ways: While the stepsize of the unrolled
algorithm matters a lot (and learning the stepsize gives a significant
improvement), the number of unrolled iterations plays a minor role
- …