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Edsger Dijkstra, Computer Scientist

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Wikimedia Commons

In our Retrobituaries series, we highlight interesting people who are no longer with us. Today let's explore the life of Edsger Dijkstra, who died at 72 in 2002. 

If you’ve used a computer or smart phone in the last few decades, you’ve come into contact with the work of Edsger Dijkstra. Since his death in 2002, his research in the field of computer science has in many ways only grown more important. Here are a few things you didn’t know about his life and his science. 

If you took his computer science class, you probably didn’t touch a computer.

Professor Dijkstra once said, “Computer science is no more about computers than astronomy is about telescopes,” and he taught his courses accordingly. He was a proponent of elegance in mathematical proofs, whereby puzzles are solved with efficiency and aesthetic sensitivity.

Grades were determined by the final exam, which was neither written on a piece of paper nor typed on a computer. Rather, students were given individual oral examinations in his office or at his home. The conversational exams lasted hours at a time, and students were asked how they might prove various mathematical propositions. They were then challenged to write out their proofs on a chalkboard. After the exam, students were offered a beer if they were of age, or a cup of tea, if they were not. 

He didn’t use email. Or a word processor.

Dijkstra was famous for his general rejection of personal computers. Instead of typing papers out using a word processor, he printed everything in longhand. He wrote well over a thousand essays of significant length this way, and for most of his academic career, they proliferated by ditto machine and fax. Each essay was given a number and prefixed with his initials, EWD.

Students who emailed Dijkstra were asked to include a physical mailing address in the letter. His secretary would print the message, and he would respond by hand.

Computers weren’t the only technology he shunned. He refused to use overhead projectors, calling them “the poison of the educational process.”


Use Google Maps? You can thank Dijkstra.

Among his profound contributions to computer science is a solution to the “single source shortest-path problem.” The solution, generally referred to as Dijkstra’s algorithm, calculates the shortest distance between a source node and a destination node on a graph. (Here is a visual representation.) The upshot is that if you’ve ever used Google Maps, you’re using a derivation of Dijkstra’s algorithm. Similarly, the algorithm is used for communications networks and airline flight plans. 

He “owned” a nonexistent company.

In many of his more humorous essays, he described a fictional company of which he served as chairman. The company was called Mathematics, Inc., and sold mathematical theorems and their maintenance. Among the company’s greatest triumphs was proving the Riemann hypothesis (which it renamed the Mathematics, Inc. Theorem), and then it unsuccessfully attempted to collect royalties on all uses of the mathematical conjecture in the real world. Evidence was never given of the proof, of course, because it was a trade secret. Mathematics Inc. claimed to have a global market share of 75 percent.

He was the first programmer in the Netherlands.

In the 1950s, his father suggested that he attend a Cambridge course on programming an Electronic Delay Storage Automatic Calculator, or EDSAC. Dijkstra did, believing that theoretical physics (which he was studying at the time at Leiden University) might one day rely upon computers. The following year, he was offered a job at Mathematisch Centrum in Amsterdam, making him the first person in the Netherlands to be employed as something called a “programmer.” (“A programmer?” he recalled of the moment he was offered the position. “But was that a respectable profession? For after all, what was programming? Where was the sound body of knowledge that could support it as an intellectually respectable discipline?” He was then challenged by his eventual employer to make it a respectable discipline.) 

This would later cause problems. On his marriage application in 1957, he was required to list his profession. Officials rejected his answer—”Programmer”—stating that there was no such job.

Previously on Retrobituaries: Albert Ellis, Pioneering Psychologist. See all Retrobituaries here.

Can You Figure Out How Many Triangles Are in This Picture?

Time for another brain teaser. How many triangles do you see here? A Quora user posted the image above (which we spotted on MSN) for fellow brainiacs to chew on. See if you can figure it out. We’ll wait.


So, as you can see, all the smaller triangles can combine to become bigger triangles, which is where the trick lies. If you count up every different triangle formed by the lines, you should get 24. (Don’t forget the big triangle!)

Some pedantic Quora users thought it through and realized there are even more triangles, if you really want to go there. There’s a triangle formed by the “A” in the signature in the right-hand corner, and if we’re counting the concept of triangles, the word “triangle” counts, too.

As math expert Martin Silvertant writes on Quora, “A triangle is a mathematical idea rather than something real; physical triangles are by definition not geometrically perfect, but approximations of triangles. In other words, both the pictorial triangles and the words referring to triangles are referents to the concept of a triangle.” So yes, you could technically count the word “triangle.”  (Silvertant also includes a useful graphic explaining how to find all the pictorial triangles.)

Check out the whole Quora discussion for in-depth explainers from users about their methods of figuring it out.

[h/t MSN]

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This Puzzling Math Brain Teaser Has a Simple Solution
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Fans of number-based brainteasers might find themselves pleasantly stumped by the following question, posed by TED-Ed’s Alex Gendler: Which sequence of integers comes next?

1, 11, 21, 1211, 111221, ?

Mathematicians may recognize this pattern as a specific type of number sequence—called a “look-and-say sequence"—that yields a distinct pattern. As for those who aren't number enthusiasts, they should try reading the numbers they see aloud (so that 1 becomes "one one," 11 is "two ones," 21 is "one two, one one,” and so on) to figure the answer.

Still can’t crack the code? Learn the surprisingly simple secret to solving the sequence by watching the video below.


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