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Stanford Lecture: Donald Knuth—"(3/2)-ary Trees" (2014)

stanfordonline · Youtube · 131 HN points · 1 HN comments
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Youtube Summary
Donald Knuth's 20th Annual Christmas Tree Lecture: (3/2)-ary Trees (2014)
December 2, 2014

In previous lectures Professor Knuth has discussed binary trees, ternary trees, quaternary trees, etc., which are enumerated by the coefficients of important functions called generalized binomial series of order 2, 3, 4, etc. What happens when we consider generalized binomial series of order 3/2, or of other fractional orders? The answer is pretty amazing.

Professor Knuth is the Professor Emeritus of the Art of Computer Programming at Stanford University. Dr. Knuth's classic programming texts include his seminal work The Art of Computer Programming, Volumes 1-3, widely considered to be among the best scientific writings of the century.
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You might also like Knuth's (3/2)-ary Trees: https://www.youtube.com/watch?v=P4AaGQIo0HY
Dec 08, 2014 · 131 points, 9 comments · submitted by mushishi
hacknat
Love this man.
tcarey83
I think I might be stupid. I did not understand any of that. Am I missings something?
ecesena
I'm just at minute 15 for now, however I can recommend you this link [1] to start with binary trees. The picture also explains why the coefficient of z^3 is 5.

[1] http://cs.lmu.edu/~ray/notes/binarytrees/

brudgers
Knuth tries to inspire anyone who doesn't settle for muttering "Oh well, maybe I can find a video of a squirrel on water skis". And his material is challenging enough that eventually everyone faces the question:

What am I going to do about it?

taeric
I know I'm stupid in this regard.

My largest takeaway was just the joy of looking at the results of mathematical constructs for patterns. Not just symbolically manipulating expressions, but also simply listing the results and seeing what could be found.

That is, many of the techniques he showed involved simply recognizing patterns in output. Then, exploring the equations symbolically to see if he could explain these ideas.

Though, again, limited intelligence on my end. :)

deckar01
You probably just need a few prerequisites. Even if you did study data structures, algorithms, and combinatorics previously, you would need to have your head wrapped around the subjects to fully understand this lecture.

I would also keep in mind that Donald Knuth probably spent more than an hour before understanding the topic.

Something that I think anyone can take away from this lecture is a story of discovering new mathematical relationships. He starts with a function that correlates to a logical problem, changes the inputs in an new (strange) way, then studies the output to form a theory that connects to the original problem.

The key was recognizing old results in a new problem.

brudgers
I would also keep in mind that Donald Knuth probably spent more than...

...fifty years writing a 1comprehensive 12 chapter book on compilers. The reason: things like this are relevant to its scope

cowsandmilk
> Something that I think anyone can take away from this lecture is a story of discovering new mathematical relationships. He starts with a function that correlates to a logical problem, changes the inputs in an new (strange) way, then studies the output to form a theory that connects to the original problem.

This type of mathematical exploration seems to be the story of his life. See Quarter-imaginary base for him doing the same thing in high school.

https://en.wikipedia.org/wiki/Quater-imaginary_base

jdnier
At one point in the video he suggests (with a laugh) the name imagin-ary to go along with binary, ternary, n-ary, etc.
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