tag:blogger.com,1999:blog-20067416.post4817047518287374267..comments2015-05-22T04:37:14.926-04:00Comments on Recursivity: Alf van der Poorten (1942-2010)Jeffrey Shallitnoreply@blogger.comBlogger13125tag:blogger.com,1999:blog-20067416.post-76664222128071151422012-03-18T19:20:41.712-04:002012-03-18T19:20:41.712-04:00Klaus: could you tell us what the error was? Is ...Klaus: could you tell us what the error was? Is there a correction somewhere?Jeffrey Shallithttp://www.blogger.com/profile/12763971505497961430noreply@blogger.comtag:blogger.com,1999:blog-20067416.post-8166335428783165652012-03-18T19:11:36.714-04:002012-03-18T19:11:36.714-04:00Alf van der Poorten was a decent person. Why?
He a...Alf van der Poorten was a decent person. Why?<br />He apologized to me for his probably biggest blunder "Some determinants that should be better known", blunder which found its continuation in "Five surprisingly simple complexities" and beyond, e. g. as "personally liked miscellaneous", stubbornly upheld by authors of lesser decency.<br />Klaus LeebAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-20067416.post-87526274767040292572010-12-23T10:05:59.121-05:002010-12-23T10:05:59.121-05:00My condolences to Alf's family. My only corre...My condolences to Alf's family. My only correspondence with Alf came while a graduate student at the University of Waterloo in Canada. Alf posted me a hard copy of his beautiful paper titled "A dozen years is but a day" which he cited in his wonderful book on Fermats Last Theorem. Certainly, my dozen years (4 undergrad, 2+6 grad) as a formal student of pure mathematics in Canada seemed to last but a day...cheers to Alf's legacy!Robert Juricevicnoreply@blogger.comtag:blogger.com,1999:blog-20067416.post-76555902041235989932010-12-13T04:39:27.553-05:002010-12-13T04:39:27.553-05:00I have only just heard of Alf's passing from m...I have only just heard of Alf's passing from my mathematician son, Chris, and was shocked to hear the news. Though I moved out of maths into another discipline I have very fond memories of Alf as both a lecturer, a fill-in supervisor while John Loxton was on leave and as a bridge player of dubious skill. My memories include him announcing in class that his wife was about to have a baby and he had to leave (I think Jack Grey took over the class); some outrageous bids in bridge at lunchtime; his advise to me not to mix my studies with student politics (do what I say, not do what I did!) and so on. Full of humanity and wit. Like Bill McCallum (whom I remember too, a couple of years below me) he left an indelible impression. Vale<br /><br />Neil OrmerodAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-20067416.post-84506832329010477612010-10-17T17:57:36.931-04:002010-10-17T17:57:36.931-04:00I first encountered Alf's unique style when I ...I first encountered Alf's unique style when I was on the Australian IMO (math olympiad) team and a few of us came across his wonderfully entertaining paper on Apery's proof of the irrationality of zeta(3). I assumed from his name that he was Dutch, and was then pleasantly surprised when shortly thereafter I went to the IMO team send-off reception to find that Alf was there and that he lived and worked in Sydney! He told me what the p-adic numbers were, and told me that if I was ever so inclined that I should come and spend a summer working with him at Macquarie (literally, he said that if I ever wanted a job that I should call him up and ask). I took him up on his offer at the end of my first year at Melbourne University, and spent six weeks in his office annex learning about elliptic curves, the Riemann-Roch theorem, the Weil conjectures, and, of course, a lot of great stuff about recurrence relations (Skolem-Mahler-Lech) and continued fractions. I also spent a non-trivial amount of time playing a game called "daleks" that was on the Macintosh SE on my desk (Alf's old computer). Near the end of my visit I had succeeded in surpassing all the previous high scores. Then, during one of my conversations with Alf in his office, I discovered that he also had daleks on his newer computer, and his current high scores put mine to shame. I also remember the time he came in briefly to work and announced that he was going home again to watch the cricket!<br /><br />I never saw him give any formal lectures, but we had conversations that ranged over many topics, from mathematical cranks to the personalities of various famous mathematicians, from how to pronunce "Thue" (Too a, or not Too a?) to finding all elliptic curves of conductor 11. I always appreciated the time he spent talking to me - it was clear that he cared a great deal about young Australian mathematicians. I'm sure I picked up my frequent use of te phrase "a priori" from his papers, although I haven't used "inter alia" as yet.<br /><br />Having planned to visit Sydney next year for the first time since '95, I'm very sad that I won't get a chance to catch up with Alf. I will always remember him fondly.Frankhttp://www.blogger.com/profile/04670664988313247780noreply@blogger.comtag:blogger.com,1999:blog-20067416.post-6165664186914933242010-10-14T02:12:25.329-04:002010-10-14T02:12:25.329-04:00Here are some comments about Alf that I made on th...Here are some comments about Alf that I made on the occasion of his 60th birthday conference:<br /><br />I first met Alf when I came to the University of New South Wales in 1974. Like Alf, I was not one those people who knew from age 5 that they wanted to be a mathematician. I came to UNSW to do a science degree, and could easily have gone into biology, chemistry, or physics. However, the moment I saw Alf walk into a crowded lecture theatre of 300 noisy undergraduates, light up a cigarette, and, with a few quite words of command, bring the room to silence—at that moment, I knew I wanted to be a mathematician.<br /><br />I remember vividly those lectures in the autumn of 1974, watching the steady flow of elegant mathematical arguments flow from Alf's pen onto<br />the overhead projector in his characteristic crisp calligraphy. It was Alf who showed me that mathematics could be beautiful and deep—and suave and sophisticated.<br /><br />Later in my undergraduate career, Alf passed on to me some of his other passions—transcendence theory, Catalan's equation, science fiction. I still have his copy of Wilson Tucker's 'The Year of the<br />Quiet Sun' (or one of his copies, at any rate). Actually, it's quite a coup to have one of Alf's books, he's very posessive about them. Once when I was leaving his office with a mathematics book he stopped me to make sure his name was in it. There was indeed a name in it—George Szekeres's, to be precise.<br /><br />According to David Hunt, there's a play in bridge which to this day is known in the UNSW mathematics department as a 'van der Poorten'. Jack Gray contends that Alf's greatest and lasting contribution to the world of the mind is his formalisation of the rules of Swedish Eights, a game centered around schadenfreude. Another of Alf's passions was his passion for football. David Tacon reports that the first time he discovered Alf was human was when they went to a St. George Rugby League match together and Alf loudly abused the<br />referee during the entire match (which, of course, St. George lost).Bill McCallumhttp://www.blogger.com/profile/09647093331377576865noreply@blogger.comtag:blogger.com,1999:blog-20067416.post-69876956443508522802010-10-13T23:16:18.987-04:002010-10-13T23:16:18.987-04:00I am saddened to hear of Alf's passing. We of...I am saddened to hear of Alf's passing. We often shared a wry smile and his ready wit made each encounter one to remember. He was a polarizing and charismatic individual.<br /><br />His farewell letter to "friends, colleagues and coconspirators" was a classic. <br /><br />Bon voyage Alf, we are the better for having known you.JtHhttp://www.blogger.com/profile/14593202017333851851noreply@blogger.comtag:blogger.com,1999:blog-20067416.post-58202993905321679902010-10-13T05:54:28.745-04:002010-10-13T05:54:28.745-04:00Jeff, Heartfelt thanks for writing this lovely tri...Jeff, Heartfelt thanks for writing this lovely tribute for my father Alf. This memorial and the comments and emails of his colleagues from all round the world have been a great comfort for Joy and the rest of us. After a difficult couple of years it is nice to remember the old Alf in all his wit and glory. Long may he live in everyone's memories.<br /><br />David van der PoortenDavidhttp://www.blogger.com/profile/10465511132482512492noreply@blogger.comtag:blogger.com,1999:blog-20067416.post-42658961526400576322010-10-12T07:59:29.344-04:002010-10-12T07:59:29.344-04:00If you instead require that the continued fraction...If you instead require that the <i>continued fraction</i> should be generated by a finite automaton, what do you get?<br /><br />(C.f. coefficients aren't bounded a priori as base-k digits are, so maybe you actually want to write the coefficients in unary and separate them by zeros, or something of the sort.)Gareth McCaughanhttp://www.blogger.com/profile/05377158305586280009noreply@blogger.comtag:blogger.com,1999:blog-20067416.post-91096018426370937882010-10-11T22:49:19.637-04:002010-10-11T22:49:19.637-04:00Jeff, thanks for posting this tribute to my collea...Jeff, thanks for posting this tribute to my colleague, Alf van der Poorten.Gerry Myersonnoreply@blogger.comtag:blogger.com,1999:blog-20067416.post-47642562549936676942010-10-11T19:54:51.993-04:002010-10-11T19:54:51.993-04:00An automatic number is one whose base-k expansion ...An automatic number is one whose base-k expansion is generated by a finite automaton. The automaton should accept the base-j expansion of i and return the i'th digit.Jeffrey Shallithttp://www.blogger.com/profile/12763971505497961430noreply@blogger.comtag:blogger.com,1999:blog-20067416.post-73030744713855412722010-10-11T19:13:15.984-04:002010-10-11T19:13:15.984-04:00Alf sounds like a great character. I'm glad yo...Alf sounds like a great character. I'm glad you had the opportunity to work with him. Anyone who loves TeX gets points in my book.<br /><br />What is an automatic number?Paul C. Anagnostopoulosnoreply@blogger.comtag:blogger.com,1999:blog-20067416.post-55285212640273819222010-10-11T17:22:11.361-04:002010-10-11T17:22:11.361-04:00Thank you for writing this tribute to Alf! As a fo...Thank you for writing this tribute to Alf! As a former student of his, I was perhaps too naive mathematically (and perhaps socially) to appreciate all of the character that was Alf. His colleagues and friends recount a different side of Alf that I was only tangentially aware of as a student. But I do nevertheless remember him fondly for his highly entertaining talks and for promoting the idea that one must always "sneak up" on a mathematical problem and to not scare it away with too much machinery. Thanks again for taking the time to remember him so honestly and vividly.William Harthttp://www.blogger.com/profile/18416881057216462316noreply@blogger.com