Donald Knuth's 2022 'Christmas Tree' Lecture Is About Trees

Like a visit from an old friend, it's Donald Knuth's annual Christmas tree lecture for 2022. "Because of the pandemic, it's been three years since Knuth has been able to honor this tradition," notes The New Stack:2022 marks the 60th anniversary of that fateful day in 1962 when a 24-year-old Donald Knuth started writing " The Art of Computer Programming." Now approaching his 85th birthday, Knuth has become almost a legend in the world of computer programming - and he's still writing additional volumes for his massive analysis of algorithms. But every year, right around Christmas time, there's another tradition. Knuth gives a special lecture "pitched at non-specialists" for a small audience at Stanford University (where Knuth is a professor emeritus) and a larger audience online... Hunched over a notepad (which was projected onto a screen behind him), Knuth began the 26th annual Christmas lecture by pointing out that the evening's topic had been hiding in plain sight for two decades. For the first 20 years, they'd called them the "Christmas tree" lectures, since "trees are one of the most important things to a computer scientist. And every year I learned at least two new cool things about trees..." About five years ago they'd changed the name to just "Christmas lectures" - but the problem wasn't that trees stopped being interesting. "I still learn cool things about trees every year. But they're getting harder and harder to explain to a general audience!" So this year's triumphant "homecoming" lecture would indeed include trees - specifically a phenomenon Knuth describes as "twintrees," along with Baxter permutations, and Floorplans. Knuth noted they're all topics touched on in the latest volume of The Art of Computer Programming, before jokingly reminding the audience that his book makes an excellent Christmas present. By the end of the lecture, Knuth had written algorithms for all three mathematical concepts - then connected all three algorithms with Linux pipes to show what happens when you convert one kind of sequence into the other and then into the other. "I get back, of course, the one I started with!"

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