View source for Leslie Valiant

{{Short description|British American computer scientist}}
{{redirect-distinguish|Les Valiant|Valiant (disambiguation)}}
{{EngvarB|date=August 2014}}
{{Use dmy dates|date=August 2014}}
{{Infobox scientist
| name              = Leslie Valiant
| honorific_suffix  = {{post-nominals|country=GBR|FRS|size=100}}
| birth_name        = Leslie Gabriel Valiant
| image             = Leslie Valiant (34913684313).jpg
| caption           = Valiant in 2011
| birth_date        = {{birth date and age|df=yes|1949|03|28}}
| birth_place       = [[Budapest]], [[Hungarian Republic (1946–49)|Hungarian Republic]]
| death_date        = 
| death_place       = 
| nationality       = British
| fields            = [[Mathematics]]<br />[[Theoretical computer science]]<br />[[Computational learning theory]]<br /> [[Theoretical neuroscience]]
| workplaces        = {{Plainlist|
* [[Harvard University]]
* [[University of Edinburgh]]}}
| education         = {{ubl |[[King's College, Cambridge]] ([[Bachelor of Arts|BA]]) |[[Imperial College London]] ([[Master of Science|MS]]) |[[University of Warwick]] ([[Doctor of Philosophy|PhD]])}}
| website = {{URL|https://people.seas.harvard.edu/~valiant}}
| doctoral_advisor  = [[Mike Paterson]]<ref name="mathgene">{{MathGenealogy|id= 18757}}</ref>
| doctoral_students = {{Plainlist|
* [[Mark Jerrum]]
* [[Michael Kearns (computer scientist)|Michael Kearns]]
* [[Dan Roth]]<ref name="mathgene"/>}}
| known_for         = {{Plainlist|
* [[Valiant–Vazirani theorem]]<ref>{{Cite journal | last1 = Valiant | first1 = L. | last2 = Vazirani | first2 = V.| doi = 10.1016/0304-3975(86)90135-0 | title = NP is as easy as detecting unique solutions | url = http://www.cs.princeton.edu/courses/archive/fall05/cos528/handouts/NP_is_as.pdf| journal = Theoretical Computer Science | volume = 47 | pages = 85–93 | year = 1986 | doi-access = free }}</ref>
* [[Counting problem (complexity)|Counting problem]]<ref>{{Cite journal | doi = 10.1137/0208032| title = The Complexity of Enumeration and Reliability Problems| journal = [[SIAM Journal on Computing]] | volume = 8| issue = 3| pages = 410–421| year = 1979| last1 = Valiant | first1 = L. G.}}</ref>
* [[Probably approximately correct learning]]
}}
| awards            = {{Plainlist|
* [[Turing Award]] (2010)
* [[EATCS Award]] (2008)
* [[Member of the National Academy of Sciences]] (2001)
* [[Knuth Prize]] (1997)
* [[AAAI Fellow]] (1992)
* [[Nevanlinna Prize]] (1986)}}
| thesis_title      = Decision Procedures for Families of Deterministic Pushdown Automata
| thesis_url        = http://wrap.warwick.ac.uk/34701/
| thesis_year       = 1974
}}

'''Leslie Gabriel Valiant''' {{post-nominals|country=GBR|FRS}}<ref name=frs>{{cite web|url=https://royalsociety.org/people/leslie-valiant-12451/|title=Leslie Valiant FRS|publisher=[[Royal Society]]|location=London|year=1991}}</ref><ref name="royal">[http://royalsociety.org/DServe/dserve.exe?dsqIni=Dserve.ini&dsqApp=Archive&dsqDb=Catalog&dsqCmd=show.tcl&dsqSearch=(RefNo==%27EC%2F1991%2F35%27) DServe Archive Catalog Show<!-- Bot generated title -->]</ref> (born 28 March 1949) is a British American<ref name="turingAward" /> computer scientist and [[computational theorist]].<ref>{{Cite journal | last1 = Hoffmann | first1 = L. | title = Q&A: Leslie Valiant discusses machine learning, parallel computing, and computational neuroscience| doi = 10.1145/1953122.1953152 | journal = [[Communications of the ACM]]| volume = 54 | issue = 6 | pages = 128 | year = 2011 | doi-access = free }}</ref><ref name=whoswho>{{Who's Who | author=Anon| title=Valiant, Prof. Leslie Gabriel | id = U40928 | year = 2017 | doi =10.1093/ww/9780199540884.013.U40928 | edition = online [[Oxford University Press]]|location=Oxford}}</ref> He was born to a chemical engineer father and a translator mother.<ref>{{Cite web |title=A. M. Turing Award Oral History Interview with Leslie Gabriel Valiant |url=https://amturing.acm.org/pdf/ValiantTuringTranscript.pdf}}</ref> He is currently the T. Jefferson Coolidge Professor of Computer Science and Applied Mathematics at [[Harvard University]].<ref name="acm">{{ACM Portal|id= 81100502250}}</ref><ref>{{Cite book | doi = 10.1145/1536414.1536415| chapter = The work of Leslie Valiant| title = Proceedings of the 41st annual ACM symposium on Symposium on theory of computing - STOC '09| pages = 1–2| year = 2009| last1 = Wigderson | first1 = A. | isbn = 9781605585062| s2cid = 15370663}}</ref><ref name="dblp">{{DBLP|name=Leslie G. Valiant}}</ref><ref>{{Cite journal | last1 = Valiant | first1 = Leslie | date = 1984 | title = A theory of the learnable | journal = Communications of the ACM | volume = 27 | issue = 11 | pages = 1134–1142  | url = http://web.mit.edu/6.435/www/Valiant84.pdf | doi=10.1145/1968.1972| s2cid = 12837541 }}</ref> Valiant was awarded the [[Turing Award]] in 2010, having been described by the [[Association for Computing Machinery|A.C.M.]] as a heroic figure in theoretical computer science and a role model for  his courage and creativity in addressing some of the deepest unsolved problems in science; in particular for his "striking combination of depth and breadth".<ref name="turingAward" />

==Education==
Valiant was educated at [[King's College, Cambridge]],<ref name="CV">{{cite web |title=CV of Leslie G. Valiant |url=http://people.seas.harvard.edu/~valiant/cv-9-3-14.pdf |website=Harvard University |access-date=January 9, 2019}}</ref><ref name="turingAward">{{cite web |title=Leslie G. Valiant - A.M. Turing Award Laureate |url=https://amturing.acm.org/award_winners/valiant_2612174.cfm |website=A.M. Turing Award |access-date=January 9, 2019}}</ref> [[Imperial College London]],<ref name="CV" /><ref name="turingAward" /> and the [[University of Warwick]] where he received a PhD in computer science in 1974.<ref>{{cite thesis|degree=PhD|publisher=University of Warwick|title=Decision procedures for families of deterministic pushdown automata|first= Leslie|last=Valiant|date=1973|url=http://wrap.warwick.ac.uk/34701/|id={{EThOS|uk.bl.ethos.475930}}|website=warwick.ac.uk|oclc=726087468}}</ref><ref name="mathgene"/>

==Research and career==
Valiant is world-renowned for his work in [[Theoretical Computer Science]]. Among his many contributions to [[computational complexity theory|Complexity Theory]], he introduced the notion of [[Sharp-P-complete|#P-completeness]] ("Sharp-P completeness") to explain why enumeration and reliability problems are intractable. He created the [[Probably Approximately Correct]] or PAC model of learning that introduced the field of [[Computational Learning Theory]] and became a theoretical basis for the development of [[Machine Learning]]. He also introduced the concept of [[holographic algorithm|Holographic Algorithms]] inspired by the [[Quantum computation|Quantum Computation]] model. In computer systems, he is most well-known for introducing the [[Bulk Synchronous Parallel]] processing model. Analogous to the von Neumann model for a single computer architecture, BSP has been an influential model for parallel and distributed computing architectures. Recent examples are [[Google]] adopting it for computation at large scale via [[MapReduce]], MillWheel,<ref>[https://research.google/pubs/pub41378/  MillWheel: Fault-Tolerant Stream Processing at Internet Scale]</ref> Pregel<ref>[https://research.google/pubs/pub37252/ Pregel: a system for large-scale graph processing]</ref> and [[Google Cloud Dataflow|Dataflow]], and [[Facebook]] creating a graph analytics system capable of processing over 1 trillion edges.<ref>[https://engineering.fb.com/2016/10/19/core-data/a-comparison-of-state-of-the-art-graph-processing-systems/  A comparison of state-of-the-art graph processing systems].</ref><ref>[https://research.facebook.com/publications/one-trillion-edges-graph-processing-at-facebook-scale/ One Trillion Edges: Graph Processing at Facebook-Scale]</ref> There have also been active open-source projects to add explicit BSP programming as well as other high-performance parallel programming models derived from BSP. Popular examples are [[Apache Hadoop|Hadoop]], [[Apache Spark|Spark]], [[Apache Giraph|Giraph]], [[Apache Hama|Hama]], [[Apache Beam|Beam]] and [[Dask_(software)|Dask]]. His earlier work in [[Automata Theory]] includes an [[CYK algorithm#Valiant's algorithm|algorithm for context-free parsing]], which is still the asymptotically fastest known. He also works in [[Computational Neuroscience]] focusing on understanding memory and learning.

Valiant's 2013 book is ''[[Probably approximately correct learning|Probably Approximately Correct: Nature's Algorithms for Learning and Prospering in a Complex World]]''.<ref>https://www.hachettebookgroup.com/titles/leslie-valiant/probably-approximately-correct/9780465037902/?lens=basic-books, {{ISBN|9780465032716}}</ref> In it he argues, among other things, that evolutionary biology does not explain the rate at which evolution occurs, writing, for example, "The evidence for Darwin's general schema for evolution being essentially correct is convincing to the great majority of biologists. This author has been to enough natural history museums to be convinced himself. All this, however, does not mean the current theory of evolution is adequately explanatory. At present the theory of evolution can offer no account of the rate at which evolution progresses to develop complex mechanisms or to maintain them in changing environments."

Valiant started teaching at [[Harvard University]] in 1982 and is currently the T. Jefferson Coolidge Professor of Computer Science and Applied Mathematics in the [[Harvard School of Engineering and Applied Sciences]].  Prior to 1982 he taught at [[Carnegie Mellon University]], the [[University of Leeds]], and the [[University of Edinburgh]].

===Awards and honors===
Valiant received the [[Nevanlinna Prize]] in 1986, the [[Knuth Prize]] in 1997, the [[EATCS Award]] in 2008,<ref>David Peleg [https://www.eatcs.org/index.php/eatcs-award/625 The EATCS Award 2008 – Laudatio for Professor Leslie Valiant] European Association of Theoretical Computer Science.</ref> and the [[Turing Award]] in 2010.<ref>Josh Fishman [http://chronicle.com/blogs/wiredcampus/probably-approximately-correct-inventor-from-harvard-u-wins-turing-award/30211 "‘Probably Approximately Correct’ Inventor, From Harvard U., Wins Turing Award"] ''Chronicle of Higher Education'' 9 March 2011.</ref><ref>[http://www.acm.org/news/featured/turing-award-2010 ACM Turing Award Goes to Innovator in Machine Learning] ACM Computing News</ref> He was elected a [[Fellow of the Royal Society|Fellow of the Royal Society (FRS)]] in 1991,<ref name=frs/> a Fellow of the [[Association for the Advancement of Artificial Intelligence|Association for the Advancement of Artificial Intelligence (AAAI)]] in 1992,<ref>[https://www.aaai.org/Awards/fellows-list.php Elected AAAI Fellows] Association for the Advancement of Artificial Intelligence.</ref> and a member of the [[United States National Academy of Sciences]] in 2001.<ref>[http://www.nasonline.org/member-directory/members/40085.html Member Directory: Leslie G. Valiant] National Academy of Sciences.</ref> Valiant's nomination for the [[Royal Society]] reads:

{{blockquote|Leslie Valiant has contributed in a decisive way to the growth of theoretical computer science. His work is concerned mainly with quantifying mathematically the resource costs of solving problems on a computer. In early work (1975), he found the asymptotically fastest algorithm known for recognising context-free languages. At the same time, he pioneered the use of communication properties of graphs for analysing computations. In 1977, he defined the notion of ‘sharp-P’ (#P)-completeness and established its utility in classifying counting or enumeration problems according to computational tractability. The first application was to counting matchings (the matrix permanent function). In 1984, Leslie introduced a definition of inductive learning that, for the first time, reconciles computational feasibility with the applicability to nontrivial classes of logical rules to be learned. This notion, later called ‘probably approximately correct learning’, became a theoretical basis for the development of machine learning. In 1989, he formulated the concept of bulk synchronous computation as a unifying principle for parallel computation. Leslie received the Nevanlinna Prize in 1986, and the Turing Award in 2010.<ref>https://royalsociety.org/people/leslie-valiant-12451/ Royal Society biography</ref>}}

The citation for his A.M. Turing Award reads:

{{blockquote|For transformative contributions to the theory of computation, including the theory of probably approximately correct (PAC) learning, the complexity of enumeration and of algebraic computation, and the theory of parallel and distributed computing.<ref name="turingAward" />}}

==Personal life==
His two sons  Gregory Valiant<ref>[http://theory.stanford.edu/~valiant/ Gregory Valiant Homepage<!-- Bot generated title -->]</ref> and Paul Valiant<ref>[https://www.cs.purdue.edu/homes/pvaliant/ Paul Valiant's homepage<!-- Bot generated title -->]</ref> are both also theoretical computer scientists.<ref name=whoswho/>

==References==
{{Reflist|35em}}

== External links ==
{{CC-notice|cc=by4|url= https://royalsociety.org/people/leslie-valiant-12451/}}

{{FRS 1991}}
{{Turing Award laureates}}
{{EATCS Award laureates}}
{{Knuth Prize laureates}}
{{Nevanlinna Prize winners}}

{{Authority control}}

{{DEFAULTSORT:Valiant, Leslie}}
[[Category:1949 births]]
[[Category:Living people]]
[[Category:Members of the United States National Academy of Sciences]]
[[Category:Turing Award laureates]]
[[Category:Nevanlinna Prize laureates]]
[[Category:Knuth Prize laureates]]
[[Category:British computer scientists]]
[[Category:Theoretical computer scientists]]
[[Category:Alumni of the Department of Computing, Imperial College London]]
[[Category:Alumni of the University of Warwick]]
[[Category:Academics of the University of Edinburgh]]
[[Category:Harvard John A. Paulson School of Engineering and Applied Sciences faculty]]
[[Category:Fellows of the Royal Society]]
[[Category:Fellows of the Association for the Advancement of Artificial Intelligence]]
[[Category:Fellows of the American Association for the Advancement of Science]]
[[Category:People from Belmont, Massachusetts]]
[[Category:Scientists from Budapest]]