Discovering errors in Donald Knuth’s TAOCP
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10 Comments
WillAdams
Nice! When I reported an error and a point of improvement in _Digital Typography_ the address was printed and glued on, not hand-written, which somewhat detracts from the display of the check/envelope.
Need to find another error so I can get an account….
nwellnhof
The inventor of the bug bounty.
jgrahamc
I have a Knuth cheque from back when he sent out real cheques. Or at least I did; for some reason I decided that cashing it was a good idea and so I have his note back to me and a photocopy of the actual cheque.
zabzonk
A long while back I wrote an answer on Stack Overflow to a question that asked "How to read TAOCP?" my answer looked something like this:
– don't read them
– get all the books, put them in a bin bag and shake vigorously with some lumps of coal, to give them that "used" look
– go through the books, underline things at random and make notes (also at random) in the margin such as "how true", or even better "wrong!"
– put books on shelf in office – never look at them again
This has worked for me, though I must admit that Searching & Sorting and stuff about random numbers are pretty good.
I got my copies free from Addison Wesley for doing some book reviews for them – not reviewing Knuth, needless to say!
nickdrozd
Great post. Some general takeaways for people who want Knuth checks:
1. You are unlikely to find errors in the algorithms themselves, especially if they've been officially published. You might find some infelicities, but these are not counted as full errors. For example, the author here found some confusing-but-not-wrong comments about local variables and unused registers. These are counted as "suggestions" (worth 0x20¢) rather than "errors" (worth 0x$1.00).
2. Knuth is pretty generous with credit — if your suggestion leads him to find an error, you get credit for the error. The author here said that some defined variables went unused. Knuth pointed out that those variables were in fact used in an exercise. However, in looking this up he noticed a variable-related error in that exercise. Author is credited with 0x$1.00!
3. Exercises are more likely to contain errors and infelicities than the main text. And there are an awful lot of exercises.
4. Knuth includes a whole bunch of stuff in his books that is not related to CS. Lots of weird trivia and references. This stuff is more likely to be wrong than the main text. For example, Knuth mentions "icosahedral objects inscribed with Greek letters" and includes a reference to an article in the Bulletin de l’Institut français du Caire. But the author points out that the article is actually in the Bulletin de l’Institut français d’archéologie orientale. Whoops! 0x$1.00 for you!
gblargg
Does the bank really read the amounts as hexadecimal?
jll29
I've emailed DEK to point out that the first person to break Enigma was not actually Alan M. Turing (as stated in one of the recent pre-fascicles) but the Polish mathematician Marian Rejewski (Turing's contribution was to automate the task, which was important because the rotors/settings were reconfigured by the German Wehrmacht every morning).
Bletchley Park now has a prominent bust of Rejewski that credits his accomplishment. The Polish wisely passed on their knowledge to the British to keep the intel safe, because they expected a German invasion.
On another note, I hope Professor Knuth has a continuity plan in place that ensures that his book series gets completed despite his advanced age (I'm worried about that, but tact prohibited me from asking, of course).
mmooss
OT: Will Knuth's lifetime of work be used for learning input in AI systems, and does he control that?
An AI application might make a good search interface for Knuth's opus.
ForOldHack
TOACP The Art of Computer Programming, Volumes 1~4c
https://en.wikipedia.org/wiki/The_Art_of_Computer_Programmin…
Kudos to everyone who found bugs, and got the bounty.
Congrats to everyone who used these to get their PhD-CS
svat
My Knuth checks amount to a total account balance of 0x$b.40 at his "Bank of San Seriffe" (the equivalent of eleven "errors" and two "suggestions") — mostly accumulated over a short period several years ago.
Previously, I had the impression that Knuth was some magical figure of perfection. What I realized was that the truth was more surprising: he makes the same kinds and the same frequency of errors as anyone else (in fact likely more, because every page is packed with a lot of detail); what sets him apart is that he cares so deeply about getting everything right — he has basically invited a DDoS on his time and attention, where every person in the world is strongly encouraged to write to him with errors on every page that he has ever written over several decades — and he does go back and look at all of them carefully (example: https://retrocomputing.stackexchange.com/questions/18117/whi…); and despite all this he somehow continues to function, producing new pages at a nonzero rate. After some experience with his responses (handwritten with pencil on a printout of the emails sent to him), I came away even more impressed.