250 research outputs found
Canonical Trees, Compact Prefix-free Codes and Sums of Unit Fractions: A Probabilistic Analysis
For fixed , we consider the class of representations of as sum of
unit fractions whose denominators are powers of or equivalently the class
of canonical compact -ary Huffman codes or equivalently rooted -ary plane
"canonical" trees. We study the probabilistic behaviour of the height (limit
distribution is shown to be normal), the number of distinct summands (normal
distribution), the path length (normal distribution), the width (main term of
the expectation and concentration property) and the number of leaves at maximum
distance from the root (discrete distribution)
Algorithmic counting of nonequivalent compact Huffman codes
It is known that the following five counting problems lead to the same
integer sequence~: the number of nonequivalent compact Huffman codes of
length~ over an alphabet of letters, the number of `nonequivalent'
canonical rooted -ary trees (level-greedy trees) with ~leaves, the number
of `proper' words, the number of bounded degree sequences, and the number of
ways of writing with integers
. In this work, we show that one can
compute this sequence for \textbf{all} with essentially one power series
division. In total we need at most additions and
multiplications of integers of bits, , or bit
operations, respectively. This improves an earlier bound by Even and Lempel who
needed operations in the integer ring or bit operations,
respectively
Egyptian Fractions
Any rational number can be written as the sum of distinct unit fractions. In
this survey paper we review some of the many interesting questions concerning
such 'Egyptian fraction' decompositions, and recent progress concerning them.Comment: 10 pages, survey article written for Nieuw Archief voor Wiskunde.
Comments welcome
Compositions into Powers of : Asymptotic Enumeration and Parameters
For a fixed integer base , we consider the number of compositions of
into a given number of powers of and, related, the maximum number of
representations a positive integer can have as an ordered sum of powers of .
We study the asymptotic growth of those numbers and give precise asymptotic
formulae for them, thereby improving on earlier results of Molteni. Our
approach uses generating functions, which we obtain from infinite transfer
matrices. With the same techniques the distribution of the largest denominator
and the number of distinct parts are investigated
Design and application of variable-to-variable length codes
This work addresses the design of minimum redundancy variable-to-variable length (V2V) codes and studies their suitability for using them in the probability interval partitioning entropy (PIPE) coding concept as an alternative to binary arithmetic coding. Several properties and new concepts for V2V codes are discussed and a polynomial-based principle for designing V2V codes is proposed. Various minimum redundancy V2V codes are derived and combined with the PIPE coding concept. Their redundancy is compared to the binary arithmetic coder of the video compression standard H.265/HEVC
Algorithms for Imaging Atmospheric Cherenkov Telescopes
Imaging Atmospheric Cherenkov Telescopes (IACTs) are complex instruments for ground-based -ray astronomy and require sophisticated software for the handling of the measured data. In part one of this work, a modular and efficient software framework is presented that allows to run the complete chain from reading the raw data from the telescopes, over calibration, background reduction and reconstruction, to the sky maps. Several new methods and fast algorithms have been developed and are presented. Furthermore, it was found that the currently used file formats in IACT experiments are not optimal in terms of flexibility and I/O speed. Therefore, in part two a new file format was developed, which allows to store the camera and subsystem data in all its complexity. It offers fast lossy and lossless compression optimized for the high data rates of IACT experiments. Since many other scientific experiments also struggle with enormous data rates, the compression algorithm was further optimized and generalized, and is now able to efficiently compress the data of other experiments as well. Finally, for those who prefer to store their data as ASCII text, a fast I/O scheme is presented, including the necessary compression and conversion routines. Although the second part of this thesis is very technical, it might still be interesting for scientists designing an experiment with high data rates
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