Edsger Dijkstra – The Man Who Carried Computer Science on His Shoulders

Last modified on November 03, 2020

As it grew to become out, the affirm I had taken from Nijmegen to Eindhoven arrived slack. To develop points worse, I grew to become then unable to catch the tremendous place of work within the school constructing. When I at remaining arrived for my appointment, I grew to become larger than half of an hour on the assist of agenda. The professor totally uncared for my profuse apologies and proceeded to want a plump hour for the assembly. It grew to become the primary time I met Edsger Wybe Dijkstra.

At the time of our assembly in 1975, Dijkstra grew to become 45 years quaint. The most prestigious award in computer science, the ACM Turing Award, had been conferred on him three years earlier. Almost twenty years his junior, I knew very exiguous in regards to the self-discipline—I had solely discovered what a flowchart grew to become a pair of weeks earlier. I grew to become a postdoc newly arrived from communist Poland with a background in mathematical logic and a perception to surrender within the West. I left the assembly with two guide options and a reproduction of a latest be taught article Dijkstra had written. He furthermore urged that I be taught the programming language Pascal.

Dijkstra handed away in 2002. All across the 1970s and 1980s, on the tip of his occupation, he grew to become doubtlessly mainly probably the most mentioned scientist in his self-discipline. He grew to become a pioneer and a genius whose work and ideas shaped the rising self-discipline of computer science be happy few others. It grew to become over the route of his occupation that computer science grew to become a primary worth and established self-discipline.

There is a long-lasting rigidity between the engineering peek of computer science, which is desirous about constructing utility programs and {hardware} elements, and the mathematical and logical peek, which goals to invent rigorous foundations for areas paying homage to programming. Dijkstra tried to reconcile every and every views. As a outcome, he contributed to both aspect of the divide in a assortment of main methods.

Dijkstra grew to become furthermore a most placing and irregular specific individual. He grew to become admired and criticized, in equal measure, and commented upon by nearly everybody he got here into contact with. But, regardless of his achievements, Dijkstra has repeatedly remained largely unknown outside computer science. Eighteen years after his lack of life, few of us have heard of him, even in his take pleasure in nation.

Biography

Edsger Dijkstra grew to become born in Rotterdam in 1930. He described his father, at one time the president of the Dutch Chemical Society, as “an out of the strange chemist,” and his mom as “a simply true mathematician who had no job.” In 1948, Dijkstra executed excellent outcomes when he executed secondary school on the crucial Erasmiaans Gymnasium in Rotterdam. His school diploma reveals that he earned the perfect possible grade in as a minimum six out of 13 points. He then enrolled on the University of Leiden to survey physics.

In September 1951, Dijkstra’s father urged he assist a three-week route on programming in Cambridge. It grew to become out to be an perception with a protracted way-reaching penalties. It grew to become in Cambridge that Dijkstra met the mathematician and computer scientist Adriaan van Wijngaarden, who for that motive reality equipped him a job on the Mathematisch Centrum (Mathematical Centre) in Amsterdam, which he joined the next 12 months. Dijkstra grew to become, in his take pleasure in phrases, “the primary Dutchman with the qualification ‘programmer’ on the payroll.” In 1956, he executed his critiques in Leiden. Three years later, he defended his PhD thesis, “Communication with an Automated Computer.” His supervisor grew to become van Wijngaarden.

Dijkstra labored on the Mathematisch Centrum till 1962, when he moved to Eindhoven to steal the verbalize of professor within the arithmetic division of the Eindhoven University of Technology. In 1973, he lowered his employment to ultimately each week and for the ultimate 4 days labored as a be taught fellow on the Burroughs Corporation, at that time an progressive American computer producer. His solely obligations for Burroughs alive to mission be taught and touring to the US a pair of occasions every and every year to lope to the agency headquarters.

In Dijkstra’s experiences, he listed the care for Plataanstraat 5, Nuenen 4565, The Netherlands. This led some to steal that the Burroughs Corporation had opened a model latest place of work. The care for grew to become, mainly, that of Dijkstra’s dwelling, a modest dwelling situated in a village discontinuance to the outskirts of Eindhoven. His place of work consisted of a exiguous room on the 2nd floor, which grew to become geared up with an “natty transportable Olivetti typewriter” and “two telephones … certainly one of which he could presumably presumably nicely expend to call wherever on the earth, with the payments going challenge to Burroughs.”

In 1984, disenchanted with a swap of route on the Burroughs Corporation and an absence of toughen for computer science at his school, Dijkstra left the Netherlands and took up a prestigious chair in computer science on the University of Texas at Austin. “Whereas Burroughs’s psychological horizon grew to become shy,” he later wrote, “my take pleasure in grew to become widening.” He retired in 1999.

In early 2002, Dijkstra discovered that he grew to become terminally sick and moved assist to Nuenen alongside along with his spouse, Ria. He handed away in August, factual a few months after returning. Ria died ten years later. The couple are survived by three children: Femke, Marcus, and Rutger.

Over the route of his occupation, Dijkstra wrote spherical 40 journal publications and 30 convention publications. He's listed as the only actual writer for merely about all of these works. A complete lot of of his journal papers have been factual a pair of pages extended, whereas most of his convention publications have been nonrefereed manuscripts that he launched for the duration of the Annual Global Marktoberdorf Summer season College and revealed within the school lawsuits. He furthermore wrote a handful of guide chapters and a few books.

Considered from this angle, Dijkstra’s be taught output seems genuine, nonetheless in each different case unremarkable by latest requirements. In this case, appearances are certainly unfounded. Judging his physique of labor on this intention misses the mark totally. Dijkstra grew to become, mainly, a extraordinarily prolific writer, albeit in an irregular method.

EWDs

In 1959, Dijkstra started writing a sequence of personal experiences. Consecutively numbered and alongside along with his initials as a prefix, they grew to become recognized as EWDs. He endured writing these experiences for larger than forty years. The remaining EWD, quantity 1,318, is dated April 14, 2002. In complete, the EWDs quantity to over 7,700 pages. Every epic grew to become photocopied by Dijkstra himself and mailed to diversified computer scientists. The recipients diversified relying on the matter. Round 20 copies of each and every EWD have been distributed on this intention.

The EWDs have been within the origin written in Dutch using a typewriter. In 1972, Dijkstra switched to writing solely in English, and in 1979 he started writing them principally by hand. The EWDs consisted of be taught papers, proofs of latest or present theorems, feedback or opinions on the scientific work of others (usually critical and recurrently titled “A significantly provoke letter to…”), verbalize papers, transcripts of speeches, options on straightforward packages to conduct be taught (“Stay solely what solely it's most likely going you will presumably nicely attain”), opinions on the attribute of schooling and universities (“It's now not the job of the University to current what society asks for, nonetheless to current what society desires”), and accepted options to puzzles. Later experiences furthermore integrated occasional accounts of Dijkstra’s existence and work. A assortment of EWDs are titled “Day bolt Deliver” and current detailed descriptions of his travels to conferences (“I managed to lope to Moscow with out being dragged to the Kremlin”), summer time faculties, or bolt areas. These experiences are a wealthy present of recordsdata about Dijkstra’s habits, views, pondering, and (hand)writing. Handiest a exiguous share of the EWDs interested by be taught ever appeared in scientific journals or books.

This vogue of reporting be taught grew to become, mainly, complete for the duration of the eighteenth century. Within the 20 th century it grew to become a disarming anachronism. Then as soon as extra, it labored. In EWD1000, dated January 11, 1987, Dijkstra recounts being rapid by readers that they possessed a sixth or seventh period copy of EWD249.

Whether written using a fountain pen or typewriter, Dijkstra’s technical experiences have been restful at a streak of spherical three phrases per minute. “The the rest of the time,” he remarked, “is taken up by pondering.” For Dijkstra, writing and pondering blended into one affirm. When getting ready a model latest EWD, he repeatedly sought to invent the ultimate mannequin from the outset.

Round 1999, Hamilton Richards, a extinct colleague of Dijkstra’s in Austin, created an online scenario to raise the whole accessible EWDs and their bibliographic entries. The E. W.  Dijkstra Archive, because the scenario is recognized, furthermore affords an abundance of additional matter matter about Dijkstra, alongside aspect hyperlinks to scans of his early technical experiences, interviews, movies, obituaries, articles, and a weblog.

Despite a world search, a assortment of EWDs from the interval before 1968 have by no intention been chanced on. Varied lacking entries within the numbering intention have been, by Dijkstra’s take pleasure in admission, “occupied by paperwork that I did not complete.”

Early Contributions

Dijkstra grew to become a merely pioneer in his self-discipline. This usually led to him problems in each day existence. In his Turing Award lecture he recalled:

[I]n 1957, I married, and Dutch marriage rites require you to verbalize your occupation and I talked about that I grew to become a programmer. Nevertheless the municipal authorities of city of Amsterdam did not accept it on the grounds that there grew to become no such occupation.

Within the mid-1950s, Dijkstra conceived an natty shortest course algorithm. There have been solely a few computer science journals on the time and discovering someplace to put up his three-page epic proved a great distance from straightforward. Eventually, three years later, he settled on the newly established Numerische Mathematik. “A Yell on Two Complications in Connexion with Graphs” stays certainly one of mainly probably the most extraordinarily cited papers in computer science, whereas Dijkstra’s algorithm has develop into priceless in GPS navigation programs for computing the shortest route between two areas.

Over a interval of eight months beginning in December 1959, Dijkstra wrote an ALGOL 60 compiler with Jaap Zonneveld. Theirs grew to become the primary compiler for this latest and very progressive programming language. It grew to become a excellent achievement. In direct to jot down the compiler, a number of challenges wished to be overcome. The most evident matter the pair confronted grew to become that the machine designated to bustle the making use of, the Dutch Electrologica X1 computer, had a reminiscence of solely 4,096 phrases. By comparability, the reminiscence of a recent-day computer computer is greater by a element of one million.

The programming language itself grew to become now not with out its take pleasure in challenges. ALGOL 60 integrated a sequence of latest good points, paying homage to recursion, which grew to become supported in a rather a lot further superior method than logicians had ever envisaged. One among the many ideas urged by Dijkstra, termed a show, addressed the implementation of recursive procedures and has since change right into a mature technique in compiler writing.

ALGOL 60 grew to become designed by a world committee. Although Dijkstra attended a number of conferences for the duration of the develop route of, his title does now not seem amongst the 13 editors of the ultimate epic. Apparently, he disagreed with a assortment of majority opinions and withdrew from the committee. This grew to become presumably the primary public sign of his fiercely held independence.

All over his employment on the Eindhoven University of Technology, Dijkstra and his group wrote an working draw for the Electrologica X8, the successor to the X1. The draw they created, recognized because the THE multiprogramming draw (THE is an abbreviation of Technische Hogeschool Eindhoven), had an progressive layered purposeful constructing, by which the elevated layers depended solely on the lower ones.

It grew to become for the duration of his work on this technique that Dijkstra’s pursuits started transferring to parallel packages, of which THE is an early instance. These packages embody a assortment of elements, every and every of which is a mature program, accomplished in parallel. Such packages are notoriously refined to jot down and analyze as a result of they must work as a result of it might presumably presumably nicely be regardless of the execution speeds of their elements. Parallel packages furthermore must synchronize their actions to develop certain extraordinary entry to assets. If a number of print jobs are dispatched on the similar time by the purchasers of a shared computer group, this must restful now not result in pages from the diversified print jobs turning into interspersed. Adding to the complexity, the elements of parallel packages must restful now not develop into deadlocked, ready indefinitely for one one different.

Within the early 1960s, these problems had now not however been successfully examined or analyzed, nor had any packages been developed to have a examine seemingly options. Dijkstra recognized a vital synchronization matter, which he named the mutual exclusion matter, and revealed his answer in a single-page paper. This work grew to become taken from EWD123, an intensive 87-page epic titled “Cooperating Sequential Processes.” Within the identical epic, he launched the primary recognized synchronization extinct, which he termed a semaphore, that resulted in a rather a lot further environment friendly intention to the mutual exclusion matter. He furthermore recognized the deadlock matter, which he named the lethal embody, and proposed an natty answer, the banker’s algorithm. The mutual exclusion matter, alongside with deadlock detection and prevention, are actually the most important points in packages on working programs and parallel programming.

In 1968, Dijkstra revealed a two-page letter addressed to the editor of the Communications of the ACM, by which he critiqued the goto programming assertion. Entitled “Scuttle To Observation Regarded as Injurious,” the letter grew to become broadly criticized and generated substantial debate. Within the discontinue, Dijkstra’s views prevailed. Every programmer is now conscious that using the goto assertion ends in so-called spaghetti code. Java, proper now certainly one of mainly probably the most broadly inclined programming languages, grew to become within the origin launched in 1996 and does now not have the goto assertion. The phrase “thought to be sinister” continues to be inclined usually in computer science and stays inextricably linked to Dijkstra.

In 1968, Dijkstra suffered a protracted, deep despair that persevered for nearly half of a 12 months. He later made level out of being hospitalized for the duration of this interval. One motive on the assist of Dijkstra’s torment grew to become that his division did not want into legend computer science essential and disbanded his group. He furthermore wanted to guage what to work on subsequent. Dijkstra’s vital utility duties, the ALGOL 60 compiler and the THE multiprogramming draw, had given him a way that programming grew to become an affirm with its take pleasure in ideas. He then tried to witness these ideas and up to date them in a crucial method. Above all, he strove to remodel programming true right into a mathematical self-discipline, an endeavor that saved him busy for a number of years to advance. At the time, these have been totally uncharted waters. No individual else appeared as if it could be devoting their consideration to such points.

A 12 months later, the seems of the 87-page EWD249, “Notes on Structured Programming,” marked the discontinue of Dijkstra’s despair. The matter of the EWD grew to become so latest, the writing so partaking, and the latest time period “structured programming” so convincing that the epic grew to become a vast success. Nevertheless, in Dijkstra’s peek, “IBM … stole the time period ‘Structured Programming’ and … trivialized the distinctive principle to the abolishment of the goto assertion.” The reveal grew to become unsurprising to these attentive to Dijkstra’s prolonged-held and largely detrimental views towards IBM computer systems and utility. At the 2nd it's miles hardly ever out of the strange to have a examine similar criticisms of tall firms, nonetheless within the 1970s and 1980s few lecturers have been able to want a public stand towards computer producers.

In 1972, Dijkstra purchased the ACM Turing Award, broadly thought to be the most important prize in computer science. He grew to become acknowledged for

main contributions to programming as a excessive, psychological matter; for eloquent insistence and helpful demonstration that packages must be restful as a result of it might presumably presumably nicely be, now not factual debugged into correctness; for illuminating perception of problems on the foundations of program develop.

Further main contributions have been to comply with. In 1974, Dijkstra revealed a two-page article by which he launched a model latest principle: self-stabilization. Within the paper, he posed the matter of how a draw of speaking machines could presumably presumably nicely restore itself when a non everlasting fault arises in certainly one of many machines. He launched latest protocols that assured simply true functioning of the draw would at remaining be restored. “Self-stabilization,” he remarked, “…could presumably presumably nicely be of relevance on a scale starting from a world group [emphasis added] to complete bus defend watch over.” Here's a placing grunt when one considers that the World Wide Net grew to become developed factual 15 years later. Because it grew to become out, the paper grew to become totally uncared for till 1983, when Leslie Lamport careworn out its significance in an invited focus on. In time, the ideas outlined by Dijkstra would result in the emergence of a full latest dwelling in distributed computing with its take pleasure in annual workshops and conferences. In 2002, the paper received an award that grew to become posthumously renamed the Edsger W. Dijkstra Prize in Distributed Computing.

The perception that some occasions can now not be deterministically predicted, usually recurrently known as indeterminism, has saved philosophers, and later physicists, occupied for hundreds of years. Computer scientists enter the memoir further now not too extended in the past, discovering out the idea that below the title nondeterminism—now not a reference, it might presumably presumably nicely be crucial, to any probabilistic interpretation of occasions. In 1963, John McCarthy launched nondeterminism within the context of programming languages. Just a number of years later, Robert Floyd confirmed how this perception, now recognized as angelic nondeterminism, can significantly simplify programming obligations requiring a search. When picks come up there's some computation that delivers the required outcome—regardless of the undeniable fact that it's miles hardly ever specific which one.

Dijkstra’s peek of nondeterminism grew to become seemingly influenced by the inherently nondeterministic habits of the trusty-time interrupt handler he developed in his PhD thesis. In a 1975 paper, he launched a exiguous programming language that he known as guarded instructions; it encapsulated what's now termed demonic nondeterminism. This grew to become, mainly, the paper he handed me the primary time I met him. Not just like the angelic variant, all computations must challenge the required outcome. This further anxious peek of nondeterminism—recurrently known as nondeterminacy by Dijkstra—usually yields further environment friendly packages, nonetheless for causes diversified than angelic nondeterminism. The programmer is free to lope away some decisions unspecified.

The programming notation launched by Dijkstra usually ends in natty packages. He illustrated this level by reconsidering Euclid’s 2,300-year-old usual algorithm for computing the most important complete divisor of two pure numbers. The algorithm shall be talked about as follows: as extended as the two numbers fluctuate, defend subtracting the smaller quantity from the larger one. In Dijkstra’s language this algorithm shall be written in a straightforward method that is now not a great distance eradicated from its description in English. His language furthermore launched the the most important perception of a guard, which has since change right into a pure principle in diversified programming formalisms. Equally, weakest precondition semantics, a principle Dijkstra launched to exclaim program semantics, marked a slack nonetheless extraordinarily crucial entry into the self-discipline of program verification. Just a number of years later, the language grew to become generalized by Tony Hoare to assemble a extraordinarily influential programming language proposal for distributed computing that he named CSP.

Dijkstra’s landmark guide A Discipline of Programming grew to become revealed in 1976. It launched a latest potential to programming by which Dijkstra blended weakest precondition semantics with a assortment of heuristics to develop a number of computer packages, hand in hand with their correctness proofs. In incompatibility with EWD249, “Notes on Structured Programming,” he grew to become now arguing about program correctness in a correct method. This type marked a model latest stage in Dijkstra’s be taught. He now seen the progress of a simply true program because the progress of a mathematical proof, one factor to which he first alluded in 1973 as section of EWD361, “Programming as a Discipline of Mathematical Nature.” This methodology grew to become shortly employed by Dijkstra and a group of researchers to systematically achieve diversified, usually exiguous, nontrivial packages. Not like a few of his diversified improvements, it by no intention if reality be informed caught on.

Eighties

In the early 1980s, Dijkstra cowrote two fast nonetheless influential papers by which he utilized his methodology to the systematic form of distributed packages. He furthermore sought to have this potential to programming taught to first-year school college students, and, with this goal in thoughts, place collectively an natty introductory textbook with Wim Feijen.

Dijkstra’s realization that programming could presumably presumably nicely be seen as a mathematical affirm resulted in his interest in inspecting mathematical reasoning. He tried to advance up with tips and heuristics that facilitated the invention of proofs. In a assortment of circumstances these ideas pointed him towards attention-grabbing generalizations of recognized outcomes that had one way or the other presumably perchance eluded others.

A precise instance is the Pythagorean theorem, which is taught in secondary faculties. The notion states that in a true-angled triangle the sq. of the hypotenuse, c, is equivalent to the sum of the squares of the diversified two aspects, a and b.

a2 + b2=c2

In 1940, Elisha Loomis restful as a minimum 370 proofs in The Pythagorean Proposition, beginning with the proof that appeared in Euclid’s Ingredients, written spherical 300 BCE. Original proofs usually seem to in the interim.

In 1986, Dijkstra got here up with the next generalization to arbitrary triangles, which he integrated in EWD975:

Comprise discontinuance into consideration a triangle with the aspect lengths a, b and c and the angles α, β and γ, lying reverse a, b and c. Then the indications of the expressions a2 + b2c2 and α + β – γ are the identical (that is, they're both every and every decided or every and every zero or every and every detrimental).

sign(a2 + b2 – c2) = sign(α + β – γ)

A mathematician could presumably presumably nicely inquire of that this all seems reasonably evident. But, curiously, nobody had notion of this generalization before Dijkstra. He concluded his epic by gazing that it grew to become unclear the place he could presumably presumably nicely put up this outcome. In his peek, it might presumably presumably nicely be taught at faculties as a change of the distinctive theorem. In 2009, EWD975 grew to become republished posthumously by Nieuw Archief voor Wiskunde (Original Archive for Arithmetic), the journal of the Royal Dutch Mathematical Affiliation. The five-page epic grew to become reproduced in its accepted handwritten develop.

In a 1985 lecture, “On Anthropomorphism in Science,” delivered on the University of Texas at Austin’s Philosophy Division, Dijkstra speculated that mathematicians caught to the utilization of implication as a result of they related it with place off and discontinue. “By hook or by criminal,” he observed, “within the implication ‘if A then B,’ the antecedent A is claimed to the place off and the following B with the discontinue.” He claimed that equivalence must be most well-liked over implication. This straightforward principle had resulted in his generalization of the Pythagorean theorem.

Dijkstra furthermore tried to note his methodology for creating simply true packages to systematically develop proofs of mathematical theorems. In EWD1016, “A Computing Scientist’s Attain to a Once-Deep Theorem of Sylvester’s,” he derived an natty proof of the next theorem, first conjectured in 1893 and proved 40 years later: “Comprise discontinuance into consideration a finite assortment of apparent aspects within the trusty Euclidean aircraft; these aspects are collinear or there exists a straight line via exactly 2 of them.”

One extra instance from this interval is his potential to the matter of a simply true coin. A coin toss is at likelihood of uncover certainly one of two outcomes in a simply true method. Nevertheless how can a simply true remaining outcome be executed when the coin is biased? In 1951, John von Neumann got here up with a straightforward answer. A assortment of researchers then tried to determine out straightforward packages to develop it further ambiance top quality. Dijkstra first discovered of the matter for the duration of a lecture in 1989. He solved it immediately and reasonably whereas later got here up with the intention by which to a linked matter that curiously nobody had notion of before. His intention to the linked matter shall be chanced on in EWD1071, “Making a Horny Roulette from a Most seemingly Biased Coin.” Dijkstra’s modification of von Neumann’s answer grew to become now not immediately evident and relies upon on a basic outcome from quantity perception, Fermat’s exiguous theorem. For a swap, Dijkstra submitted this text to a journal and it grew to become revealed the next 12 months as a one-page show.

The form of a pure and readable notation for representing proofs and calculations grew to become nearly as essential for Dijkstra because the problems into account. The notation he got here up with forces the writer now not to commit what he described as “any sins of omission”:

  • A
  • ={ impress why A =B }
  • B
  • ={ impress why B =C }
  • C

In his remaining EWD, as an illustration, Dijkstra explains that for s =(a + b + c)/2 the equality s(– b)(s – c) + s(s –c)(s – a) = s(s – c)c holds, by writing out his argument as:

  • s(s – b)(s – c) + s(s – c)(s – a)
  • ={ algebra }
  • s(s – c)(2s – a – b)
  • { definition of s }
  • s(s – c)c

He inclined this notation in his take pleasure in publications, notably in a guide he wrote alongside along with his longstanding buddy and colleague Carel Scholten. The notation grew to become adopted by a number of of his colleagues nonetheless did not unfold additional. EWD1300, “The Notational Conventions I Adopted, and Why,” grew to become republished posthumously and affords a selected notion into Dijkstra’s intensive work on notation, a subject that saved him busy for the duration of his occupation.

Within the slack 1980s, Dijkstra’s be taught grew to become described on his departmental homepage as follows: “My dwelling of interest focuses on the streamlining of the mathematical argument so to develop larger our powers of reasoning, in specific, by method of formal packages.” It grew to become furthermore the matter of his route for computer science school college students.

All across the interval 1987–1990, I grew to become a fellow college member in Austin and adopted his route for a semester. Dijkstra invariably arrived early for sophistication in order that he could presumably presumably nicely write out an irregular citation on the blackboard. The lectures themselves have been repeatedly meticulously prepared and repeatedly devoted to presenting proofs of straightforward mathematical outcomes. He delivered the lectures with out notes, requiring solely a blackboard and half of chalk. At the discontinue of each and every lecture he would set up an main nonetheless nontrivial mathematical matter as homework and get dangle of the whole options on the following lecture. Every week later he would return the whole options with detailed feedback, usually longer than the trusty submissions, after which latest his take pleasure in answer intimately, stressing the presentation and expend of notation. My take pleasure in options fared reasonably neatly by Dijkstra’s requirements and have been usually returned with solely fast feedback, paying homage to “Many sins of omission.” It grew to become, mainly, a route in natty mathematical pondering, and nobody appeared in any admire that it had nothing to comprehend with computer science.

Dijkstra grew to become a extraordinarily partaking lecturer. He knew straightforward packages to captivate an viewers with dramatic pauses, neatly-conceived remarks, and placing turns of phrase. The larger the viewers, the higher he carried out. While I grew to become working in Austin I helped put together a departmental match with him because the precept speaker. About 200 of us got here alongside, some having flown in from Houston and neighboring states to assist the match. Dijkstra stole the inform and delivered a enthralling presentation on Sylvester’s theorem.

Nineties

In 1990, Dijkstra’s sixtieth birthday grew to become famend in Austin with a tall feast that good points an important group of site visitors, alongside aspect a huge assortment of essential figures in computer science. A Festschrift grew to become revealed by Springer-Verlag to mark the occasion. The amount started on web page 0, in deference to the intention by which Dijkstra numbered the pages of his EWDs. He took the trouble of thanking every and every of the 61 contributing authors by a handwritten letter.

The interval that adopted grew to become marked by a visual swap in Dijkstra’s perspective and potential to his work. Within the ultimate twelve years of his existence, regardless of producing about 250 latest EWDs, he revealed nearly nothing. These experiences merely could presumably presumably nicely now not have met his requirements for a journal e-newsletter. Replace the EWDs have been devoted to systematically deriving proofs of refined outcomes, paying homage to an matter from the Global Mathematical Olympiad. He furthermore inclined his methodology to develop natty options for classical puzzles, paying homage to the knight’s tour or the wolf, goat, and cabbage puzzle. About a of the EWDs from this interval contained accounts and assessments of his early contributions.

Following Dijkstra’s retirement from instructing within the autumn of 1999, a symposium grew to become organized in Might presumably furthermore merely 2000 to honor his seventieth birthday. The match grew to become known as “In Pursuit of Simplicity” and integrated buyer contributors from every and every Europe and the US. At current, I grew to become working on the Centre for Arithmetic and Informatics (CWI) in Amsterdam and for the duration of the symposium I invited Dijkstra to current a lecture. CWI grew to become, mainly, the latest title for the Mathematisch Centrum the place he had labored on the beginning of his occupation. Six months later Dijkstra authorised the invitation. He had by no intention thought-about the latest and higher constructing the place the CWI had relocated within the early 1980s, and have become visibly moved.

Before the lecture, the CWI’s dialog division issued a press provoke. Recordsdata of the match caught the consideration of a crucial Dutch newspaper. A journalist grew to become dispatched and an intensive article with a outstanding picture of Dijkstra grew to become shortly revealed. VPRO, an honest Dutch public broadcasting agency, for that motive reality grew to become fascinated by Dijkstra and despatched a crew to Austin to develop a half of-hour-prolonged program about him. “Denken als self-discipline” (Thinking as a Discipline) grew to become broadcast in April 2001 as an episode of the science inform Noorderlicht (Northern Lights). The episode purchased a ravishing consider in a single different outstanding Dutch newspaper.

In early 2002, Dijkstra returned to Nuenen, incurably sick with most cancers. The information unfold fleet within the pc science group and have become invariably met with deep unhappiness. The remaining time I noticed Dijkstra grew to become at his dwelling in July 2002. As grew to become usually the case with site visitors, he restful me by vehicle from the closest affirm station a pair of kilometers a great distance off from his dwelling. All across the roam to, we spoke collectively, shared lunch, and he rapid me that he did not have rather a lot time left. He furthermore gave me a reproduction of EWD1318, “Coxeter’s Rabbit,” dated April 14, 2002, mentioning that it could be his remaining epic.

Dijkstra handed away a month later. His funeral grew to become attended by a assortment of his colleagues, alongside aspect a number of from Austin. In his eulogy, Hoare mirrored on Dijkstra’s enormous contributions to the progress of his self-discipline:

He would lay the foundations that may presumably nicely set computing as a rigorous scientific self-discipline; and in his be taught and in his instructing and in his writing, he would pursue perfection to the exclusion of all diversified considerations. From these commitments he by no intention deviated, and that is how he has made to his chosen matter of survey the most important contribution that somebody specific individual could presumably presumably nicely develop in somebody lifetime.

J Strother Moore, then chairman of the pc science division in Austin, furthermore spoke warmly and evocatively of Dijkstra: “He grew to become be happy a person with a gradual within the darkness. He illuminated merely about every and every matter he mentioned.”

Obituaries for that motive reality have been revealed in several principal newspapers, alongside aspect the Original York Cases, the Washington Submit, and The Guardian. Extended commemorative objects and recollections appeared for the duration of the months that adopted, by which Dijkstra grew to become variously acclaimed as a pioneer, prophet, memoir, and genius.

Opinions and Attitudes

Dijkstra’s enduring have an effect on in computer science isn't any longer confined totally to his be taught. He held regular opinions about many aspects of the self-discipline, most notably about programming languages and the instructing of programming, nonetheless furthermore the needs of schooling and be taught.

Dijkstra did not shocked a great distance off from controversies. He grew to become a devoted contrarian who reveled in expressing low and unconventional opinions. I noticed this firsthand in 1977 for the duration of a tall computer science convention in Toronto. Audiences for plenary lectures on the match numbered someplace between a number of hundred and a thousand attendees. Every of the lectures concluded with a few well mannered viewers questions for the speaker, usually a primary educated in his dwelling. I if reality be informed have a vivid recollection of Dijkstra standing up on the discontinue of 1 lecture and handing over a stinging rebuke to the speaker. Contrary to appearances, he hoped to impress an informative dialogue. The chairman grew to become visibly shocked by Dijkstra’s intervention and appeared at a loss as to how he must restful proceed.

Dijkstra grew to become furthermore unafraid to enlighten harsh critiques at smaller gatherings. Within the slack 1970s, I attended a seminar in Utrecht with about twenty diversified people, alongside aspect Dijkstra. He many occasions interrupted a extraordinarily revered lecturer to foretell him about his expend of terminology and abbreviations. Halfway via the presentation Dijkstra suddenly obtained up and left. Varied tales in a similar vein have been a great distance from out of the strange and circulated for the duration of the self-discipline.

Dijkstra took his work as a reviewer extraordinarily critically and his experiences have been detailed and fastidiously notion out. About a of these critiques have been undertaken at his take pleasure in initiative and appeared as EWDs. These integrated a decided consider of a 400-page computer science guide that had no evident connection to his be taught. He furthermore produced intensive and considerate feedback on manuscripts despatched to him by his colleagues who had adopted his notation or methodology, or whose be taught he deemed essential.

In 1977, Dijkstra wrote a vitriolic consider of a epic, “Social Processes and Proofs of Theorems and Programs,” by Richard De Millo, Richard Lipton, and Alan Perlis. The epic later appeared as a journal paper. Dijkstra distributed his consider as EWD638, “A Political Pamphlet from the Heart Ages,” by which he referred to the epic as “a really grotesque paper.” The authors had argued that “program verification is certain to fail,” a peek Dijkstra vehemently disagreed with.

About a of these critiques resulted in additional correspondence with the distinctive authors. In 1978, Dijkstra distributed an in depth and scathing consider of the 1977 Turing Award Lecture delivered by John Backus. In EWD692 he argued that the lecture “suffers badly from aggressive overselling.” At the time, Backus grew to become certainly one of mainly probably the most outstanding working computer scientists. He grew to become the co-inventor of a mature notation at likelihood of describe the syntax of programming languages, recognized as Backus–Naur develop, and had led the group that designed and utilized Fortran, the primary high-stage programming language. In his lecture, Backus had advocated for an totally different type of programming, recognized as purposeful programming. Four years in the past, Jiahao Chen chanced on an intensive and very critical correspondence between Backus and Dijkstra that occurred following the consider. Dijkstra correctly saved these exchanges a great distance off from the ultimate public search.

In some quarters, Dijkstra grew to become seen as immodest and his opinions thought to be low. When cataloguing their correspondence in his papers, Backus added the remark: “This man’s shallowness takes your breath away.” For tons of, particularly of us who adopted his notation, Dijkstra grew to become a establish equivalent to a guru. A exiguous group of his followers even began their take pleasure in EWD-be happy experiences, all consecutively numbered and written by hand. Dijkstra appeared detached to such shows. “Nevertheless he takes himself so critically,” a Turing Award winner as soon as confided to me. Indeed, one usually had the impression that he carried the burden of computer science on his shoulders.

In 1984, I grew to become invited to be a lecturer on the annual Marktoberdorf College, co-organized by Dijkstra. Although I regarded this as a huge honor, I'll presumably presumably nicely now not abet nonetheless if reality be informed really feel anxious about having him assessing my work. His consider appeared in EWD895, “Day bolt epic E. W. Dijkstra, Marktoberdorf, 30 July–12 Aug. 1984.” I grew to become tremendously relieved to witness his feedback have been now not solely considerably light, nonetheless even reasonably decided in comparability to his diversified critiques: “Honest’s lectures suffered significantly from this [i.e., talking ‘exclusively about CSP’] … The examples chosen as an illustration his aspects have been reasonably elaborate, nonetheless his conscious efforts to be understood have been extraordinarily favored.”

Impressed by this appraisal, I submitted certainly one of many papers I had launched to a take into legend-reviewed journal. Just a number of months later, the anonymous referee experiences arrived. One among the many critiques grew to become unmistakably the work of Dijkstra. An in depth criticism of what he thought to be an absence of sufficiently formal arguments, blended with a protracted document of calls for and questions, made trying top quality revisions a hopeless job. Even at current time, I would not know straightforward packages to meet these calls for for the reason that true formalism continues to be missing. At the time, it grew to become nonetheless thought to be a privilege to have a paper refereed by Dijkstra.

In 1989, Dijkstra launched his views on instructing computer programming in a lecture titled “On the Cruelty of In actuality Educating Computer Science” for the duration of an ACM Computer Science Convention. A transcript grew to become later circulated as EWD1036. After presenting a sweeping historic look geared towards illustrating mature resistance towards latest ideas in science, Dijkstra argued that computer programming must be taught in a radically diversified method. His proposal grew to become to educate some of the elements of mathematical logic, want a exiguous nonetheless extraordinarily environment friendly programming language, after which pay attention in on the job of developing provably simply true computer packages. In his peek, packages must be thought to be the identical method as formulation, whereas programming must be taught as a department of arithmetic. There grew to become no place for operating packages or for testing, every and every of which have been thought to be frequent follow in utility engineering.

The lecture and epic resulted in an intensive debate that additionally makes for attention-grabbing discovering out. Dijkstra’s epic grew to become revealed in Communications of the ACM, collectively alongside along with his well mannered nonetheless unapologetic responses to principally detrimental reactions from outstanding computer scientists. While he grew to become praised for initiating a a lot-wanted debate, Dijkstra’s options have been deemed unrealistic and too controversial.

Dijkstra usually expressed his opinions using memorable turns of phrase or maxims that caught the ears of his colleagues and have been broadly commented upon. Here are some examples:

  • Program testing shall be at likelihood of inform the presence of bugs, nonetheless by no intention to inform their absence.
  • Computer science is now not any further about computer systems than astronomy is prepared telescopes.
  • The quiz of whether or not or now not machines can decide is prepared as related because the quiz of whether or not or now not submarines can swim.
  • A components is value a thousand pictures.

In certainly one of his EWDs, Dijkstra restful a number of jibes about programming languages, paying homage to: “The utilization of COBOL cripples the thoughts; its instructing must restful, for that motive reality, be thought to be towards the regulation.” At the time, COBOL grew to become certainly one of mainly probably the most broadly inclined programming languages and these feedback have been now not warmly purchased.

About a of Dijkstra’s opinions have been unavoidably controversial and highlighted his longstanding prejudices. When I first met him in 1975 he rapid the guide Structured Programming, nonetheless urged that I skip the ultimate chapter by Hoare and Ole-Johan Dahl, as a result of it handled object-oriented programming. Then as soon as extra, object-oriented programming progressively grew to become a universally most well-liked method to constructing a tall program. Nevertheless now not for Dijkstra. He grew to become restful arguing towards it in 1999, declaring for the duration of a keynote care for that, “For people who've puzzled: I don’t decide object-oriented programming is a structuring paradigm that meets my requirements of sophistication.” By that time, the accepted object-oriented programming language C++ grew to become routinely taught to first-year computer science school college students.

Persona and Everyday life

Throughout his skilled occupation, Dijkstra remained remarkably modest. He by no intention had a secretary; he typed or wrote all his publications himself. Most have been solely his take pleasure in work and even the few that listed coauthors have been clearly written by Dijkstra, or in his vogue. After 1979, he most well-liked to jot down by hand using a Montblanc fountain pen. His writing vogue grew to become so recognizable amongst computer scientists within the 1980s {that a} fellow tutorial, Luca Cardelli, designed a Dijkstra font for Macintosh computer systems. No longer extended after it grew to become launched, Dijkstra purchased a letter typeset in Cardelli’s font and mistakenly assumed it grew to become handwritten. He felt tricked by the letter and have become now not amused. Some years later, he grew to become able to adore the humor when a colleague in Austin, Bob Boyer, adopted the font for shows for the duration of departmental conferences.

It seems Dijkstra by no intention utilized for any grants—regardless of the undeniable fact that he did obtain on the very least one, to expend a PhD scholar—nor did he elevate any cash, within the develop of be taught contracts, to the establishments he labored for. He furthermore by no intention purchased a computer. Eventually, within the slack 1980s, he grew to become given one as a gift by a computer agency, nonetheless by no intention inclined it for bear in mind processing. Dijkstra did not take pleasure in a TV, a VCR, or perchance a mobile phone. He most well-liked to defend a great distance off from the cinema, citing an oversensitivity to visible enter. By incompatibility, he loved attending classical music live performance occasions.

When taking section in conferences and summer time faculties Dijkstra usually felt unfortunate in tall groups. Unaccustomed to exiguous focus on, he usually remained awkwardly restful. Some distance flung from the work ambiance, nonetheless, he grew to become totally diversified. From his time in Austin, I and others raise him as top quality, priceless, and wanting to tumble by alongside along with his spouse for a short lived social roam to that usually resulted in partaking conversations. He and his spouse cherished to ask site visitors over, for whom he usually performed fast objects of classical music on his Bösendorfer piano. His favorite composer grew to become Mozart. A placing attribute of Dijkstra’s dwelling room grew to become a lectern with a tall copy of the Oxford English Dictionary, which he chanced on priceless in his work. He's, by the intention by which, talked about in the identical dictionary in reference to the utilization of the phrases vector and stack in computing.

In Austin, Dijkstra stayed a great distance off from school politics. He grew to become extraordinarily revered by colleagues, now not least because of his collegial perspective for the duration of departmental conferences. He took his instructing obligations very critically. Assessments have been repeatedly oral and can remaining a pair of hours. Upon completion of the examination, an off-the-cuff chat adopted all by which the scholar grew to become launched with a signed picture of Dijkstra, and a beer—age allowing. He held his weekly seminars in his place of work and served espresso to the faculty college students in attendance, usually evil them alongside along with his unassuming habits.

For the size of his existence, Dijkstra grew to become an uncompromising perfectionist, repeatedly desirous about tapping his creativity, unwilling to decrease his requirements, and detached towards totally different aspects of peek. He furthermore chanced on it refined to browse articles in his self-discipline to develop an perception of their contents and appeared bored to lack of life in monitoring down and discovering out the related literature. For mainly probably the most section, he adopted the options of his discontinuance colleagues and solely studied the papers they urged. As a outcome, his take pleasure in papers usually had solely a few, if any, bibliographic entries. The preface of A Discipline of Programming concludes with a frank admission: “For the absence of a bibliography I provide neither clarification nor apology.” This cavalier potential resulted in occasional complaints from colleagues who chanced on that their work grew to become uncared for.

As a change, Dijkstra most well-liked to survey basic texts, paying homage to Eric Temple Bell’s Men of Arithmetic, which he referred to usually for the duration of his packages in Austin, and Linus Pauling’s Normal Chemistry, a guide he praised in highest phrases. This perspective served him neatly for the duration of the 1960s and 1970s, nonetheless it little question grew to become further and additional impractical as computer science matured.

Published in 1990, Dijkstra’s Predicate Calculus and Program Semantics, cowritten with Scholten, grew to become a for instance. The guide now not solely lacked references, nonetheless furthermore exhibited a complete brush aside for the work of logicians. Egon Börger penned an intensive and devastating consider, claiming that the potential outlined by the authors grew to become now not in any method latest, nor did it provide any benefits. He furthermore vigorously criticized the guide’s rudimentary historical past of predicate logic, by which the authors drew a line from the work of Gottfried Leibniz to that of George Boole after which to their take pleasure in contributions, neglecting to level out another person.

Primarily based on Börger’s consider, some colleagues tried to abet by publishing papers that equipped a purposeful logical consider and clarification of Dijkstra and Scholten’s potential per their so-called calculational proofs. Dijkstra remained unrepentant. “I by no intention felt obliged to placate the logicians,” he remarked some years later in EWD1227. “If nonetheless, [logicians] solely get dangle of infuriated as a result of I don’t play my sport in keeping with their ideas,” he added, referring specifically to Börger’s consider, “I'll now not withstand the temptation to disregard their fury and to shrug my shoulders in mainly probably the most well mannered method.”

Dijkstra’s humorousness grew to become, at turns, wry and terse. I as soon as requested him what number of PhD school college students he had. “Two,” he spoke again, before including, “Einstein had none.” On one different occasion, he wrote to me that “[redacted] strengthened the Division by leaving it.” In Austin, collectively alongside along with his spouse, he purchased a Volkswagen bus, dubbed the Touring Machine, which they at likelihood of discover nationwide parks.

Dijkstra grew to become furthermore extraordinarily merely. He grew to become repeatedly insistent, as an illustration, that the primary intention to the mutual exclusion matter grew to become chanced on by his colleague Th. J. Dekker. In EWD1308, he admitted that F. E. J. Kruseman Aretz “restful chanced on and repaired a assortment of errors [in the ALGOL 60 compiler] after I had left the Mathematical Centre in 1962,” and that the phrase “thought to be sinister” grew to become, mainly, invented by an editor of the Communications of the ACM, Niklaus Wirth. Dijkstra’s contribution grew to become within the origin titled “A Case towards the GO TO Observation.” Within the identical EWD, he furthermore admitted totally lacking the significance of Floyd and Hoare’s preliminary contributions to program verification. “I grew to become if reality be informed behind” he lamented.

Legacy

Dijkstra left on the assist of a excellent array of notions and ideas which have withstood the test of time: the show, the mutual exclusion matter, the semaphore, lethal embody, the banker’s algorithm, the dozing barber and the eating philosophers problems, self-stabilization, weakest precondition, guard, and structured programming.

His shortest course algorithm is taught

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