38 research outputs found
Shellsort with three increments
A perturbation technique can be used to simplify and sharpen A. C. Yao's
theorems about the behavior of shellsort with increments . In
particular, when and , the average
running time is . The proof involves interesting properties of
the inversions in random permutations that have been -sorted and -sorted
Average-Case Complexity of Shellsort
We prove a general lower bound on the average-case complexity of Shellsort:
the average number of data-movements (and comparisons) made by a -pass
Shellsort for any incremental sequence is \Omega (pn^{1 + 1/p) for all . Using similar arguments, we analyze the average-case complexity
of several other sorting algorithms.Comment: 11 pages. Submitted to ICALP'9
Zig-zag Sort: A Simple Deterministic Data-Oblivious Sorting Algorithm Running in O(n log n) Time
We describe and analyze Zig-zag Sort--a deterministic data-oblivious sorting
algorithm running in O(n log n) time that is arguably simpler than previously
known algorithms with similar properties, which are based on the AKS sorting
network. Because it is data-oblivious and deterministic, Zig-zag Sort can be
implemented as a simple O(n log n)-size sorting network, thereby providing a
solution to an open problem posed by Incerpi and Sedgewick in 1985. In
addition, Zig-zag Sort is a variant of Shellsort, and is, in fact, the first
deterministic Shellsort variant running in O(n log n) time. The existence of
such an algorithm was posed as an open problem by Plaxton et al. in 1992 and
also by Sedgewick in 1996. More relevant for today, however, is the fact that
the existence of a simple data-oblivious deterministic sorting algorithm
running in O(n log n) time simplifies the inner-loop computation in several
proposed oblivious-RAM simulation methods (which utilize AKS sorting networks),
and this, in turn, implies simplified mechanisms for privacy-preserving data
outsourcing in several cloud computing applications. We provide both
constructive and non-constructive implementations of Zig-zag Sort, based on the
existence of a circuit known as an epsilon-halver, such that the constant
factors in our constructive implementations are orders of magnitude smaller
than those for constructive variants of the AKS sorting network, which are also
based on the use of epsilon-halvers.Comment: Appearing in ACM Symp. on Theory of Computing (STOC) 201
Ada style guide (version 1.1)
Ada is a programming language of considerable expressive power. The Ada Language Reference Manual provides a thorough definition of the language. However, it does not offer sufficient guidance on the appropriate use of Ada's powerful features. For this reason, the Goddard Space Flight Center Ada User's Group has produced this style guide which addresses such program style issues. The guide covers three areas of Ada program style: the structural decomposition of a program; the coding and the use of specific Ada features; and the textural formatting of a program