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A framework for adaptive algorithm selection in STAPL
 IN PROC. ACM SIGPLAN SYMP. PRIN. PRAC. PAR. PROG. (PPOPP), PP 277–288
, 2005
"... Writing portable programs that perform well on multiple platforms or for varying input sizes and types can be very difficult because performance is often sensitive to the system architecture, the runtime environment, and input data characteristics. This is even more challenging on parallel and distr ..."
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Writing portable programs that perform well on multiple platforms or for varying input sizes and types can be very difficult because performance is often sensitive to the system architecture, the runtime environment, and input data characteristics. This is even more challenging on parallel and distributed systems due to the wide variety of system architectures. One way to address this problem is to adaptively select the best parallel algorithm for the current input data and system from a set of functionally equivalent algorithmic options. Toward this goal, we have developed a general framework for adaptive algorithm selection for use in the Standard Template Adaptive Parallel Library (STAPL). Our framework uses machine learning techniques to analyze data collected by STAPL installation benchmarks and to determine tests that will select among algorithmic options at runtime. We apply a prototype implementation of our framework to two important parallel operations, sorting and matrix multiplication, on multiple platforms and show that the framework determines runtime tests that correctly select the best performing algorithm from among several competing algorithmic options in 86100 % of the cases studied, depending on the operation and the system.
On the adaptiveness of quicksort
 IN: WORKSHOP ON ALGORITHM ENGINEERING & EXPERIMENTS, SIAM
, 2005
"... Quicksort was first introduced in 1961 by Hoare. Many variants have been developed, the best of which are among the fastest generic sorting algorithms available, as testified by the choice of Quicksort as the default sorting algorithm in most programming libraries. Some sorting algorithms are adapti ..."
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Quicksort was first introduced in 1961 by Hoare. Many variants have been developed, the best of which are among the fastest generic sorting algorithms available, as testified by the choice of Quicksort as the default sorting algorithm in most programming libraries. Some sorting algorithms are adaptive, i.e. they have a complexity analysis which is better for inputs which are nearly sorted, according to some specified measure of presortedness. Quicksort is not among these, as it uses Ω(n log n) comparisons even when the input is already sorted. However, in this paper we demonstrate empirically that the actual running time of Quicksort is adaptive with respect to the presortedness measure Inv. Differences close to a factor of two are observed between instances with low and high Inv value. We then show that for the randomized version of Quicksort, the number of element swaps performed is provably adaptive with respect to the measure Inv. More precisely, we prove that randomized Quicksort performs expected O(n(1+log(1+ Inv/n))) element swaps, where Inv denotes the number of inversions in the input sequence. This result provides a theoretical explanation for the observed behavior, and gives new insights on the behavior of the Quicksort algorithm. We also give some empirical results on the adaptive behavior of Heapsort and Mergesort.
A framework for speeding up priorityqueue operations
, 2004
"... Abstract. We introduce a framework for reducing the number of element comparisons performed in priorityqueue operations. In particular, we give a priority queue which guarantees the worstcase cost of O(1) per minimum finding and insertion, and the worstcase cost of O(log n) with at most log n + O ..."
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Abstract. We introduce a framework for reducing the number of element comparisons performed in priorityqueue operations. In particular, we give a priority queue which guarantees the worstcase cost of O(1) per minimum finding and insertion, and the worstcase cost of O(log n) with at most log n + O(1) element comparisons per minimum deletion and deletion, improving the bound of 2log n + O(1) on the number of element comparisons known for binomial queues. Here, n denotes the number of elements stored in the data structure prior to the operation in question, and log n equals max {1,log 2 n}. We also give a priority queue that provides, in addition to the abovementioned methods, the prioritydecrease (or decreasekey) method. This priority queue achieves the worstcase cost of O(1) per minimum finding, insertion, and priority decrease; and the worstcase cost of O(log n) with at most log n + O(log log n) element comparisons per minimum deletion and deletion. CR Classification. E.1 [Data Structures]: Lists, stacks, and queues; E.2 [Data
Adaptive sorting with AVL trees
, 2004
"... Abstract A new adaptive sorting algorithm is introduced. The new implementation relies on using the traditional AVL trees, and has the same performance limitations. More precisely, the number of comparisons performed by our algorithm, on an input sequence of length n that has I inversions, is at ..."
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Abstract A new adaptive sorting algorithm is introduced. The new implementation relies on using the traditional AVL trees, and has the same performance limitations. More precisely, the number of comparisons performed by our algorithm, on an input sequence of length n that has I inversions, is at most 1.44n lg I n + O(n) 1. Our algorithm runs in time O(n log I n) and is practically efficient and easy to implement. 1.
On the Adaptiveness of Quicksort Gerth Sto/lting Brodal*, # Rolf Fagerberg##, $ Gabriel Moruz*
, 2004
"... Abstract Quicksort was first introduced in 1961 by Hoare. Many variantshave been developed, the best of which are among the fastest generic sorting algorithms available, as testified by the choice of Quicksort asthe default sorting algorithm in most programming libraries. Some sorting algorithms are ..."
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Abstract Quicksort was first introduced in 1961 by Hoare. Many variantshave been developed, the best of which are among the fastest generic sorting algorithms available, as testified by the choice of Quicksort asthe default sorting algorithm in most programming libraries. Some sorting algorithms are adaptive, i.e. they have a complexity analysiswhich is better for inputs which are nearly sorted, according to some specified measure of presortedness. Quicksort is not among these, asit uses \Omega ( n log n) comparisons even when the input is already sorted.However, in this paper we demonstrate empirically that the actual running time of Quicksort is adaptive with respect to the presortednessmeasure Inv. Differences close to a factor of two are observed between instances with low and high Inv value. We then show that for the randomized version of Quicksort, the number of element swaps performed is provably adaptive with respect to the measure Inv. More precisely,we prove that randomized Quicksort performs expected O(n(1+log(1+Inv /n))) element swaps, where Inv denotes the number of inversionsin the input sequence. This result provides a theoretical explanation
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, 2006
"... Theoretical and practical efficiency of priority queues ..."
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Abstract On the Adaptiveness of Quicksort
"... variants have been developed, the best of which are among the fastest generic sorting algorithms available, as testified by the choice of Quicksort as the default sorting algorithm in most programming libraries. Some sorting algorithms are adaptive, i.e. they have a complexity analysis which is bett ..."
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variants have been developed, the best of which are among the fastest generic sorting algorithms available, as testified by the choice of Quicksort as the default sorting algorithm in most programming libraries. Some sorting algorithms are adaptive, i.e. they have a complexity analysis which is better for inputs which are nearly sorted, according to some specified measure of presortedness. Quicksort is not among these, as it uses Ω(n log n) comparisons even when the input is already sorted. However, in this paper we demonstrate empirically that the actual running time of Quicksort is adaptive with respect to the presortedness measure Inv. Differences close to a factor of two are observed between instances with low and high Inv value. We then show that for the randomized version of Quicksort, the number of element swaps performed is provably adaptive with respect to the measure Inv. More precisely, we prove that randomized Quicksort performs expected O(n(1 + log(1 + Inv/n))) element swaps, where Inv denotes the number of inversions in the input sequence. This result provides a theoretical explanation for the observed behavior, and gives new insights on the behavior of the Quicksort algorithm. We also give some empirical results on the adaptive behavior of Heapsort and Mergesort. 1