58,439 research outputs found
Walking Faster in a Triangulation
Point location in a triangulation is one of the most studied problems in computational geometry. For a single query, stochastic walk is a good practical strategy. In this work, we propose two approaches improving the performance of the stochastic walk. The first improvement is based on a relaxation of the exactness of the predicate, whereas the second is based on termination guessing.La localisation d'un point dans une triangulation est un des problèmes les plus étudiés en géométrie algorithmique. Pour un petit nombre de requêtes, la marche stochastique est une bonne stratégie en pratique. Dans ce travail, nous proposons deux idées qui améliorent les performances de la marche stochastique. La première est basée sur une relaxation de l'exactitude du prédicat d'orientation, tandis que la deuxième est basée sur lune tentative de divination de la longueur de cette marche
One machine, one minute, three billion tetrahedra
This paper presents a new scalable parallelization scheme to generate the 3D
Delaunay triangulation of a given set of points. Our first contribution is an
efficient serial implementation of the incremental Delaunay insertion
algorithm. A simple dedicated data structure, an efficient sorting of the
points and the optimization of the insertion algorithm have permitted to
accelerate reference implementations by a factor three. Our second contribution
is a multi-threaded version of the Delaunay kernel that is able to concurrently
insert vertices. Moore curve coordinates are used to partition the point set,
avoiding heavy synchronization overheads. Conflicts are managed by modifying
the partitions with a simple rescaling of the space-filling curve. The
performances of our implementation have been measured on three different
processors, an Intel core-i7, an Intel Xeon Phi and an AMD EPYC, on which we
have been able to compute 3 billion tetrahedra in 53 seconds. This corresponds
to a generation rate of over 55 million tetrahedra per second. We finally show
how this very efficient parallel Delaunay triangulation can be integrated in a
Delaunay refinement mesh generator which takes as input the triangulated
surface boundary of the volume to mesh
The centers of gravity of the associahedron and of the permutahedron are the same
In this article, we show that Loday's realization of the associahedron has
the the same center of gravity than the permutahedron. This proves an
observation made by F. Chapoton. We also prove that this result holds for the
associahedron and the cyclohedron as realized by the first author and C. Lange
Angular Scale Expansion Theory And The Misperception Of Egocentric Distance In Locomotor Space
Perception is crucial for the control of action, but perception need not be scaled accurately to produce accurate actions. This paper reviews evidence for an elegant new theory of locomotor space perception that is based on the dense coding of angular declination so that action control may be guided by richer feedback. The theory accounts for why so much direct-estimation data suggests that egocentric distance is underestimated despite the fact that action measures have been interpreted as indicating accurate perception. Actions are calibrated to the perceived scale of space and thus action measures are typically unable to distinguish systematic (e.g., linearly scaled) misperception from accurate perception. Whereas subjective reports of the scaling of linear extent are difficult to evaluate in absolute terms, study of the scaling of perceived angles (which exist in a known scale, delimited by vertical and horizontal) provides new evidence regarding the perceptual scaling of locomotor space
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