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Charles E. Leiserson

Bio: Charles E. Leiserson is an academic researcher from Massachusetts Institute of Technology. The author has contributed to research in topics: Cilk & Scheduling (computing). The author has an hindex of 65, co-authored 185 publications receiving 49312 citations. Previous affiliations of Charles E. Leiserson include Vassar College & Carnegie Mellon University.


Papers
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Proceedings ArticleDOI
03 Nov 1982
TL;DR: A novel organization of raster-graphics memory that permits all small rectangles to be moved efficiently is proposed that is based on a doubly periodic assignment of pixels to M memory chips according to a "Fibonacci" lattice.
Abstract: A high-resolution raster-graphics display is usually combined with processing power and a memory organization that facilitates basic graphics operations. For many applications, including interactive text processing, the ability to quickly move or copy small rectangles of pixels is essential. This paper proposes a novel organization of raster-graphics memory that permits all small rectangles to be moved efficiently. The memory organization is based on a doubly periodic assignment of pixels to M memory chips according to a "Fibonacci" lattice. The memory organization guarantees that if a rectilinearly oriented rectangle contains fewer than M/√5 pixels, then all pixels will reside in different memory chips, and thus can be accessed simultaneously. We also define a continuous amdogue of the problem which can be posed as, "What is the maximum density of a set of points in the plane such that no two points are contained in the interior of a rectilinearly oriented rectangle of area N." We give a lower bound of 1/2N on the density of such a set, and show that 1/√5N can be achieved.

19 citations

Journal ArticleDOI
18 Jul 2016
TL;DR: Prism-R is presented, a variation of Prism that executes dynamic data-graph computations deterministically even when updates modify global variables with associative operations, and is only marginally slower than Prism.
Abstract: A data-graph computation—popularized by such programming systems as Galois, Pregel, GraphLab, PowerGraph, and GraphChi—is an algorithm that performs local updates on the vertices of a graph. During each round of a data-graph computation, an update function atomically modifies the data associated with a vertex as a function of the vertex’s prior data and that of adjacent vertices. A dynamic data-graph computation updates only an active subset of the vertices during a round, and those updates determine the set of active vertices for the next round.This article introduces Prism, a chromatic-scheduling algorithm for executing dynamic data-graph computations. Prism uses a vertex coloring of the graph to coordinate updates performed in a round, precluding the need for mutual-exclusion locks or other nondeterministic data synchronization. A multibag data structure is used by Prism to maintain a dynamic set of active vertices as an unordered set partitioned by color. We analyze Prism using work-span analysis. Let G = (V, E) be a degree-Δ graph colored with χ colors, and suppose that Q⊆V is the set of active vertices in a round. Define size(Q)= vQv + ∑v∈ Q deg(v), which is proportional to the space required to store the vertices of Q using a sparse-graph layout. We show that a P-processor execution of Prism performs updates in Q using O(χ (lg ( Q/χ ) + lg Δ ) + lg P span and Θ(size(Q) + P) work.These theoretical guarantees are matched by good empirical performance. To isolate the effect of the scheduling algorithm on performance, we modified GraphLab to incorporate Prism and studied seven application benchmarks on a 12-core multicore machine. Prism executes the benchmarks 1.2 to 2.1 times faster than GraphLab’s nondeterministic lock-based scheduler while providing deterministic behavior.This article also presents Prism-R, a variation of Prism that executes dynamic data-graph computations deterministically even when updates modify global variables with associative operations. Prism-R satisfies the same theoretical bounds as Prism, but its implementation is more involved, incorporating a multivector data structure to maintain a deterministically ordered set of vertices partitioned by color. Despite its additional complexity, Prism-R is only marginally slower than Prism. On the seven application benchmarks studied, Prism-R incurs a 7p geometric mean overhead relative to Prism.

18 citations

01 Jan 2011
TL;DR: Pochoir is a compiler for a domain-specific language embedded in C++ which produces excellent code from a simple specification of a desired stencil computation and automatically parallelizes and optimizes cache performance.
Abstract: Pochoir is a compiler for a domain-specific language embedded in C++ which produces excellent code from a simple specification of a desired stencil computation. Pochoir allows a wide variety of boundary conditions to be specified, and it automatically parallelizes and optimizes cache performance. Benchmarks of Pochoir-generated code demonstrate a performance advantage of 2‐10 times over standard parallel loop implementations. This paper describes the Pochoir specification language and shows how a wide range of stencil computations can be easily specified.

18 citations

Proceedings ArticleDOI
11 Jul 2018
TL;DR: Open Cilk is a new open-source platform to support Cilk multithreaded programming, especially for researchers and teachers, and will provide a streamlined runtime system and feature comprehensive static instrumentation for dynamic-analysis tools.
Abstract: Open Cilk is a new open-source platform to support Cilk multithreaded programming, especially for researchers and teachers. Open Cilk aims to provide a full-featured implementation of Cilk that is easy to modify and extend. Based on the award-winning Tapir/LLVM compiler, Open Cilk will provide a streamlined runtime system and feature comprehensive static instrumentation for dynamic-analysis tools. As a community-infrastructure project, Open Cilk encourages contributions from researchers in the areas of languages, compilers, runtime systems, tools, libraries, and benchmarks.

17 citations

Proceedings ArticleDOI
05 May 1982
TL;DR: This paper explores how large tree machines may be assembled efficiently from smaller components and presents a restructurable linear-area layout of m processors with O(lg m) pins that can realize an arbitrary binary tree.
Abstract: Many researchers have proposed that ensembles of processing elements be organized as trees. This paper explores how large tree machines may be assembled efficiently from smaller components. A principal constraint that we consider is the limited number of external connections from an integrated circuit chip. We also explore the emerging capability of restructurable VLSI which allows a chip to be customized after fabrication. We give a linear-area chip of m processors and only four off-chip connections which can be used as the sole building block to construct an arbitrarily large complete binary tree. We also present a restructurable linear-area layout of m processors with O(lg m) pins that can realize an arbitrary binary tree. This layout is based on a solution to the graph-theoretic problem: Given a tree in which each vertex is either black or white, determine how many edges need be cut in order to bisect the tree into equal-size components, each containing exactly half the black and half the white vertices.

16 citations


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Book
01 Jan 1996
TL;DR: A valuable reference for the novice as well as for the expert who needs a wider scope of coverage within the area of cryptography, this book provides easy and rapid access of information and includes more than 200 algorithms and protocols.
Abstract: From the Publisher: A valuable reference for the novice as well as for the expert who needs a wider scope of coverage within the area of cryptography, this book provides easy and rapid access of information and includes more than 200 algorithms and protocols; more than 200 tables and figures; more than 1,000 numbered definitions, facts, examples, notes, and remarks; and over 1,250 significant references, including brief comments on each paper.

13,597 citations

Proceedings Article
25 Jul 2004
TL;DR: Four different RouGE measures are introduced: ROUGE-N, ROUge-L, R OUGE-W, and ROUAGE-S included in the Rouge summarization evaluation package and their evaluations.
Abstract: ROUGE stands for Recall-Oriented Understudy for Gisting Evaluation. It includes measures to automatically determine the quality of a summary by comparing it to other (ideal) summaries created by humans. The measures count the number of overlapping units such as n-gram, word sequences, and word pairs between the computer-generated summary to be evaluated and the ideal summaries created by humans. This paper introduces four different ROUGE measures: ROUGE-N, ROUGE-L, ROUGE-W, and ROUGE-S included in the ROUGE summarization evaluation package and their evaluations. Three of them have been used in the Document Understanding Conference (DUC) 2004, a large-scale summarization evaluation sponsored by NIST.

9,293 citations

Proceedings ArticleDOI
26 Mar 2000
TL;DR: RADAR is presented, a radio-frequency (RF)-based system for locating and tracking users inside buildings that combines empirical measurements with signal propagation modeling to determine user location and thereby enable location-aware services and applications.
Abstract: The proliferation of mobile computing devices and local-area wireless networks has fostered a growing interest in location-aware systems and services. In this paper we present RADAR, a radio-frequency (RF)-based system for locating and tracking users inside buildings. RADAR operates by recording and processing signal strength information at multiple base stations positioned to provide overlapping coverage in the area of interest. It combines empirical measurements with signal propagation modeling to determine user location and thereby enable location-aware services and applications. We present experimental results that demonstrate the ability of RADAR to estimate user location with a high degree of accuracy.

8,667 citations

Journal ArticleDOI
01 Apr 2012-Fly
TL;DR: It appears that the 5′ and 3′ UTRs are reservoirs for genetic variations that changes the termini of proteins during evolution of the Drosophila genus.
Abstract: We describe a new computer program, SnpEff, for rapidly categorizing the effects of variants in genome sequences. Once a genome is sequenced, SnpEff annotates variants based on their genomic locations and predicts coding effects. Annotated genomic locations include intronic, untranslated region, upstream, downstream, splice site, or intergenic regions. Coding effects such as synonymous or non-synonymous amino acid replacement, start codon gains or losses, stop codon gains or losses, or frame shifts can be predicted. Here the use of SnpEff is illustrated by annotating ~356,660 candidate SNPs in ~117 Mb unique sequences, representing a substitution rate of ~1/305 nucleotides, between the Drosophila melanogaster w1118; iso-2; iso-3 strain and the reference y1; cn1 bw1 sp1 strain. We show that ~15,842 SNPs are synonymous and ~4,467 SNPs are non-synonymous (N/S ~0.28). The remaining SNPs are in other categories, such as stop codon gains (38 SNPs), stop codon losses (8 SNPs), and start codon gains (297 SNPs) in...

8,017 citations