2,309 research outputs found
A strip-like tiling algorithm
AbstractWe extend our previous results on the connection between strip tiling problems and regular grammars by showing that an analogous algorithm is applicable to other tiling problems, not necessarily related to rectangular strips. We find generating functions for monomer and dimer tilings of T- and L-shaped figures, holed and slotted strips, diagonal strips and combinations of them, and show how analogous results can be obtained by using different pieces
The Tiling Algorithm for the 6dF Galaxy Survey
The Six Degree Field Galaxy Survey (6dFGS) is a spectroscopic survey of the
southern sky, which aims to provide positions and velocities of galaxies in the
nearby Universe. We present here the adaptive tiling algorithm developed to
place 6dFGS fields on the sky, and allocate targets to those fields. Optimal
solutions to survey field placement are generally extremely difficult to find,
especially in this era of large-scale galaxy surveys, as the space of available
solutions is vast (2N dimensional) and false optimal solutions abound. The
6dFGS algorithm utilises the Metropolis (simulated annealing) method to
overcome this problem. By design the algorithm gives uniform completeness
independent of local density, so as to result in a highly complete and uniform
observed sample. The adaptive tiling achieves a sampling rate of approximately
95%, a variation in the sampling uniformity of less than 5%, and an efficiency
in terms of used fibres per field of greater than 90%. We have tested whether
the tiling algorithm systematically biases the large-scale structure in the
survey by studying the two-point correlation function of mock 6dF volumes. Our
analysis shows that the constraints on fibre proximity with 6dF lead to
under-estimating galaxy clustering on small scales (< 1 Mpc) by up to ~20%, but
that the tiling introduces no significant sampling bias at larger scales.Comment: 11 pages, 7 figures. Full resolution version of the paper available
from http://www.mso.anu.edu.au/6dFGS/ . Abridged version of abstract belo
Random numbers from the tails of probability distributions using the transformation method
The speed of many one-line transformation methods for the production of, for
example, Levy alpha-stable random numbers, which generalize Gaussian ones, and
Mittag-Leffler random numbers, which generalize exponential ones, is very high
and satisfactory for most purposes. However, for the class of decreasing
probability densities fast rejection implementations like the Ziggurat by
Marsaglia and Tsang promise a significant speed-up if it is possible to
complement them with a method that samples the tails of the infinite support.
This requires the fast generation of random numbers greater or smaller than a
certain value. We present a method to achieve this, and also to generate random
numbers within any arbitrary interval. We demonstrate the method showing the
properties of the transform maps of the above mentioned distributions as
examples of stable and geometric stable random numbers used for the stochastic
solution of the space-time fractional diffusion equation.Comment: 17 pages, 7 figures, submitted to a peer-reviewed journa
The Homogeneous Broadcast Problem in Narrow and Wide Strips
Let be a set of nodes in a wireless network, where each node is modeled
as a point in the plane, and let be a given source node. Each node
can transmit information to all other nodes within unit distance, provided
is activated. The (homogeneous) broadcast problem is to activate a minimum
number of nodes such that in the resulting directed communication graph, the
source can reach any other node. We study the complexity of the regular and
the hop-bounded version of the problem (in the latter, must be able to
reach every node within a specified number of hops), with the restriction that
all points lie inside a strip of width . We almost completely characterize
the complexity of both the regular and the hop-bounded versions as a function
of the strip width .Comment: 50 pages, WADS 2017 submissio
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