# Uzi Vishkin

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Uzi Vishkin | |
---|---|

Born | 1953 Tel Aviv, Israel |

Fields | parallel algorithms |

Institutions | IBM Thomas J. Watson Research Center New York University Tel Aviv University University of Maryland, College Park |

Alma mater | Hebrew University Technion |

Doctoral advisor | Yossi Shiloach |

**Uzi Vishkin** (born 1953) is a computer scientist at the University of Maryland, College Park, where he is Professor of Electrical and Computer Engineering at the University of Maryland Institute for Advanced Computer Studies (UMIACS). Uzi Vishkin is known for his work in the field of parallel computing. In 1996, he was inducted as a Fellow of the Association for Computing Machinery, with the following citation: "One of the pioneers of parallel algorithms research, Dr. Vishkin's seminal contributions played a leading role in forming and shaping what thinking in parallel has come to mean in the fundamental theory of Computer Science."^{[1]}

## Contents |

## Biography

Uzi Vishkin was born in Tel Aviv, Israel. He completed his B.Sc. (1974) and M.Sc. in Mathematics at the Hebrew University, before earning his D.Sc. in Computer Science at the Technion (1981). He then spent a year working at the IBM Thomas J. Watson Research Center in Yorktown Heights, New York. From 1982 to 1984, he worked at the department of computer science at New York University and remained affiliated with it till 1988. From 1984 until 1997 he worked in the computer science department of Tel Aviv University, serving as its chair from 1987 to 1988. Since 1988 he is with the University of Maryland, College Park.

## PRAM-on-chip

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In the 1980s and 1990s, Uzi Vishkin co-authored several articles that helped building a theory of parallel algorithms in a mathematical model called parallel random access machine (PRAM), which is a generalization for parallel computing of the standard serial computing model random-access machine (RAM). The parallel machines needed for implementing the PRAM model have not yet been built at the time, and quite a few challenged the ability to ever build such machines. Concluding in 1997^{[2]} that the transistor count on chip as implied by Moore's Law will allow building a powerful parallel computer on a single silicon chip within a decade, he developed a PRAM-On-Chip vision that called for building a parallel computer on a single chip that allows programmers to develop their algorithms for the PRAM model. He went on to invent the explicit multi-threaded (XMT) computer architecture that enables implementation of this PRAM theory, and led his research team to completing in January 2007 a 64-processor computer^{[3]} named Paraleap,^{[4]} that demonstrates the overall concept. The XMT concept was presented in Vishkin et al. (1998) and Naishlos et al. (2003) and the XMT 64-processor computer in Wen & Vishkin (2008). The demonstration comprised several hardware and software components, as well as teaching PRAM algorithms in order to program the XMT Paraleap, using a language called XMTC. Since making parallel programming easy is one of the biggest challenges facing computer science today, the demonstration also sought to include teaching the basics of PRAM algorithms and XMTC programming to students ranging from high-school to graduate school.

## Parallel algorithms

In the field of parallel algorithms, Uzi Vishkin co-authored the paper Shiloach & Vishkin (1982) that contributed the work-time (WT) (sometimes called work-depth) framework for conceptualizing and describing parallel algorithms. The WT framework was adopted as the basic presentation framework in the parallel algorithms books JaJa (1992) and Keller, Kessler & Traeff (2001), as well as in the class notes Vishkin (2009). In the WT framework, a parallel algorithm is first described in terms of parallel rounds. For each round, the operations to be performed are characterized, but several issues can be suppressed. For example, the number of operations at each round need not be clear, processors need not be mentioned and any information that may help with the assignment of processors to jobs need not be accounted for. Second, the suppressed information is provided. The inclusion of the suppressed information is, in fact, guided by the proof of a scheduling theorem due to Brent (1974). The WT framework is useful since while it can greatly simplify the initial description of a parallel algorithm, inserting the details suppressed by that initial description is often not very difficult. Similarly, first casting an algorithm in the WT framework can be very helpful for programming it in XMTC.

In the field of parallel and distributed algorithms, one of the seminal papers co-authored by Uzi Vishkin is Cole & Vishkin (1986). This work introduced an efficient parallel technique for graph coloring. The Cole–Vishkin algorithm finds a vertex colouring in an *n*-cycle in *O*(log^{*} *n*) synchronous communication rounds. This algorithm is nowadays presented in many textbooks, including *Introduction to Algorithms* by Cormen et al.,^{[5]} and it forms the basis of many other distributed algorithms for graph colouring.^{[6]}

Other contributions by Uzi Vishkin and various co-authors include parallel algorithms for list ranking, lowest common ancestor, spanning trees, and biconnected components.

## Selected publications

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- Shiloach, Yossi; Vishkin, Uzi (1982), [
**Expression error: Missing operand for >**"An*O*(log*n*) parallel connectivity algorithm"],*Journal of Algorithms***3**: 57–67. - Shiloach, Yossi; Vishkin, Uzi (1982), [
**Expression error: Missing operand for >**"An*O*(*n*^{2}log*n*) parallel max-flow algorithm"],*Journal of Algorithms***3**: 128–146. - Mehlhorn, Kurt; Vishkin, Uzi (1984), [
**Expression error: Missing operand for >**"Randomized and deterministic simulations of PRAMs by parallel machines with restricted granularity of parallel memories"],*Acta Informatica***21**: 339–374. - Tarjan, Robert; Vishkin, Uzi (1985), [
**Expression error: Missing operand for >**"An efficient parallel biconnectivity algorithm"],*SIAM Journal on Computing***14**: 862–874. - Vishkin, Uzi (1985), [
**Expression error: Missing operand for >**"Optimal parallel pattern matching in strings"],*Information and Control***67**: 91–113. - Cole, Richard; Vishkin, Uzi (1986), [
**Expression error: Missing operand for >**"Deterministic coin tossing with applications to optimal parallel list ranking"],*Information and Control***70**(1): 32–53, doi:. - Vishkin, Uzi; Dascal, Shlomit; Berkovich, Efraim; Nuzman, Joseph (1998), "Explicit Multi-Threading (XMT) bridging models for instruction parallelism",
*Proc. 1998 ACM Symposium on Parallel Algorithms and Architectures (SPAA)*, pp. 140–151, http://www.umiacs.umd.edu/users/vishkin/XMT/spaa98.ps. - Naishlos, Dorit; Nuzman, Joseph; Tseng, Chau-Wen; Vishkin, Uzi (2003), "Towards a First Vertical Prototyping of an Extremely Fine-Grained Parallel Programming Approach",
*Theory of Computer Systems (Special Issue of 2001 ACM Symp. on Parallel Algorithms and Architecture)***36**: 551–552, http://www.umiacs.umd.edu/users/vishkin/XMT/spaa01-j-03.pdf. - Wen, Xingzhi; Vishkin, Uzi (2008), "FPGA-based prototype of a PRAM-on-chip processor",
*Proc. 2008 ACM Conference on Computing Frontiers (Ischia, Italy)*, pp. 55–66, doi:, http://www.umiacs.umd.edu/users/vishkin/XMT/CompFrontiers08.pdf.

## Notes

**^**ACM: Fellows Award / Uzi Vishkin.**^**Vishkin, Uzi. Spawn-join instruction set architecture for providing explicit multithreading. U.S. Patent 6,463,527. See also Vishkin et al. (1998).**^**University of Maryland, press release, June 26, 2007: "Maryland Professor Creates Desktop Supercomputer".**^**University of Maryland, A. James Clark School of Engineering, press release, November 28, 2007: "Next Big "Leap" in Computing Technology Gets a Name".**^**1st ed., Section 30.5.**^**See, e.g., Goldberg, Plotkin & Shannon (1988).

## References

- Baase, Sara; Van Gelder, Allen (2000).
*Computer Algorithms Introduction to Design and Analysis*(Third ed.). Addison-Wesley. ISBN 0-201-61244-5. - Brent, Richard P. (1974), [
**Expression error: Missing operand for >**"The parallel evaluation of general arithmetic expressions"],*Journal of the ACM***21**: 201–208. - Cormen, Thomas H.; Leiserson, Charles E.; Rivest, Ronald L. (1990).
*Introduction to Algorithms*(First ed.). MIT Press and McGraw-Hill. ISBN 978-0-262-03141-7. - Eppstein, David; Galil, Zvi (1988), [
**Expression error: Missing operand for >**"Parallel algorithmic techniques for combinatorial computation"],*Ann. Rev. Comput. Sci***3**: 233–283

This survey paper cites 16 papers co-authored by Vishkin

- Goldberg, Andrew V.; Plotkin, Serge A.; Shannon, Gregory E. (1988), [
**Expression error: Missing operand for >**"Parallel symmetry-breaking in sparse graphs"],*SIAM Journal on Discrete Mathematics***1**(4): 434–446, doi: - JaJa, Joseph (1992).
*An Introduction to Parallel Algorithms*. Addison-Wesley. ISBN 0-201-54856-9.

Cites 36 papers co-authored by Vishkin

- Karp, Richard M.; Ramachandran, Vijaya (1988), [
**Expression error: Missing operand for >**"A Survey of Parallel Algorithms for Shared-Memory Machines"],*University of California, Berkeley, Department of EECS, Tech. Rep. UCB/CSD-88-408*

This survey paper cites 20 papers co-authored by Vishkin

- Keller, Jorg; Kessler, Cristoph W.; Traeff, Jesper L. (2001).
*Practical PRAM Programming*. Wiley-Interscience. ISBN 0-471-35351-5.

Cites 19 papers co-authored by Vishkin

- Manber, Udi (1989).
*Introduction to Algorithms A Creative Approach*. Addison-Wesley. ISBN 0-201-12037-2. **Vishkin, Uzi**(2009).*Thinking in Parallel: Some Basic Data-Parallel Algorithms and Techniques, 104 pages*. Class notes of courses on parallel algorithms taught since 1992 at the University of Maryland, College Park, Tel Aviv University and the Technion. http://www.umiacs.umd.edu/users/vishkin/PUBLICATIONS/classnotes.pdf.- Mathematics Genealogy Project: Uzi Vishkin.
- ISI Web of Knowledge, highly cited researchers: Uzi Vishkin.