The “Windmill” Problem on the 2011 International Mathematical Olympiad [video]
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Correctly proving this without assistance is one thing, but explaining it to non-mathematicians via a YouTube video sounds so difficult that some I.M.O candidates may struggle with this. Even so, I think the author is perhaps a professional/skilled mathematician or both which greatly helps explain this proof in a concise fashion.
On the other hand, I find that problems like this may be (ab)used in the future for technical interviews at financial/asset/investment management institutions for software engineering roles. Over the top indeed, but I think it would very difficult to justify using mathematical proof questions in interviews.
I'm not really worried. In general, the trend for hiring software engineers has been away from silly puzzles, not towards. Microsoft and Google both used to use them and now they don't, and other companies have been following along. In general, hiring fads and follow-the-leader are not great, but in this case it's for the best that other companies have taken their lead.
To be sure, there are still lots of other problems with how developers are hired, but the stupid puzzles at least have mostly faded away.
If you can memorize the whole world, that probably would be useful day to day too - I'm sure you'd see a lot of stuff you could use the shit you memorized for! - but it doesn't seem to be happening much.
Most of where I've see the "how would you manipulate this array" type of stuff is generalist stuff or new-to-the-particular-subdomain candidates, where if I asked for exactly what I'm looking for them to know, they'd fail. Gotta just look for people who can learn it on the fly fast instead, and I haven't found any better proxies yet. :|
[0] https://medium.com/@alexgolec/google-interview-problems-rati...
Lisa is undoubtedly brilliant. She may also very well be an amazing teacher also, I don't know. My point is just that one should not assume that.
To understand how this works, the researcher will apply for some grant, say $300,000 to study some question in geometry. Now, why does a mathematician need grant money when their only tools are a paper and pencil (maybe a laptop with Tex installed)? First, the university gets 1/3 of that money as "overhead", so the researcher is left with $200,000. Then, the researcher will pay to "buy out" his teaching load which is more money paid to the university, say $150,000 to not teach 2 classes for a year. With the remaining $50,000, he may spend money to fund a post doc to come and assist him for a semester. Again, that money goes to the university. So the researcher may get $300,000 but it all ends up in the pocket of the University, which in turn pays him a good salary with the assumption that he keeps the grants coming. A place like Stanford gets about 1/3 of its funding from these research grants, 1/3 from its endowment, and 1/3 from tuition. It hires researches to get the grants, grad students and adjuncts to teach, and the sports teams and other events help with endowment.
Thus research professors are hired on the basis of their ability to avoid teaching loads, not on their teaching skills.
Is that why she is teaching two classes in her first semester, including one which is lower division? Usually you don't put the crappy teachers in the lower division classes, you give them graduate seminars.
I appreciate your cynicism, but based on her teaching load, I'm going to guess that she is also a good teacher.
Since when? The hard-and-fast rule is junior faculty are assigned intro classes. We often give youthful teachers higher marks than crusty, doddering emeriti, perhaps for good reason, perhaps not.
> I appreciate your cynicism, but based on her teaching load, I'm going to > guess that she is also a good teacher.
GP did not question her teaching ability, but your inference of said ability from her impressive ascent at Stanford. It's a bit like inferring LeBron James must really be mature since he entered the NBA straight from high school.
Is that why she is teaching two classes in her first semester, including one which is lower division?
Not really sure what you're saying. The fact that she's teaching just means that she isn't using (or doesn't have) a research grant to `buy out' of teaching.
> Usually you don't put the crappy teachers in the lower division classes, you give them graduate seminars.
Again, I don't know where you got this idea from. Usually (in a math research department such as the one at Stanford) whoever's arranging the teaching assignments doesn't look at an instructors teaching credentials at all, unless they are egregiously bad. So all we can conclude is that she isn't absolutely awful at teaching.
The fact of the matter is that many researchers (due to their incentives) view teaching, especially lower division courses, as a chore, so really anyone in the department who wants to teach such a course is not going to get much opposition.
I am merely describing to you how this stuff works. My descriptions are accurate, from the overhead that universities take to the shifting of teaching loads onto adjuncts and grad students to the relative weight of teaching on research hires. You can verify by discussing these issues with someone else who went through the grad school experience and saw it all first hand -- I did it at Stanford.
As to why such an anodyne and factual description of reality strikes you as cynical is something you have to come to grips with. There are reasons for this system. Lots of grant money is available -- should it not be available? Should we not be funding this stuff? Given that grant money is available for research, it makes sense that specialists who are good at getting grants would be allowed to do that -- get grants -- whereas others who are good at teaching be allowed to do that. Obviously universities are going to compete to find these specialists and will pay them well. The only problem here is that when people think of Stanford as a great research institution (which it is), they just assume that is must be a great teaching college, which it isn't. It's pretty mediocre on that front, yet that's what people assume, because they think a good researcher must be a good teacher. Listen, many good researchers can't even speak english at anything approaching a college level. At Stanford. They aren't there to teach. Researchers do research, and teachers teach. That is probably the thing that is upsetting you, but really a moment's reflection should tell you that these are all simple consequences of the multiple hats a research university like Stanford is expected to wear. If you want a good education, go to a teaching college -- there are many out there.
https://professorpositions.com/szego-assistant-professor-at-...
I'm sure she will get a tt job when she wants however.
Quite a big difference
Programming is literally isomorphic to finding proofs (Curry-Howard FTW!). From the other perspective on proofs, they're about communicating technical concepts in a clear way, which is a vital skill for a developer in an organization. So no, I don't think it would be that hard to justify. I was kind of joking at first, but that's actually pretty compelling...
The cell with the maximum depth on the arrangement contains the points in the "middle", meaning they have as many points on one side, as they have on the other.
Then you can prove that a line starting on any such point will visit every other point an infinite number of times.
The proof I outlined will work for any point. Initially it might have the wrong number of points on both sides but for some rotation it will have the correct number of points on both sides.
"Knowing when the math is hard is way harder than the math itself"
But then maybe the math is hard only because it's not being explained well? (I hope it's uncontroversial to suggest that our current methods of teaching math are not the best of all possible worlds.)
I get that this problem came up in the context of of a math puzzle contest, and that some people enjoy solving puzzles. I am questioning their utility as an educational device.
I kinda think that we should teach math as fast as we can so that we can concentrate on the stuff that's really hard, not just apparently hard because someone is being coy with the easy routes.
> I am questioning their utility as an educational device.
Puzzles like this aren't found in mainstream math education contexts. As you acknowledged in your post, they are only found in math competitions. What do you mean?
Kind of, although I don't think they do it deliberately.
Things like teaching logarithms without a slide rule.
> Puzzles like this aren't found in mainstream math education contexts. As you acknowledged in your post, they are only found in math competitions. What do you mean?
You're right. Let me try again.
Check out William Bricken's "Iconic Math" http://iconicmath.com/ or "Proofs without Words" https://en.wikipedia.org/wiki/Proof_without_words or the other 3Blue1Brown videos for that matter.
I think that most math seems hard to most people only because we are not creative in the ways that it is presented. We should use science to figure out how to present math so that people get it as fast as they can, in part so that we can find and concentrate on the actually hard math problems.
E.g. Alan Kay using Smalltalk to teach calculus to little kids in the context of modelling falling objects, to me kinda proves that it shouldn't take a whole semester to teach calculus to teenagers.
Yes, those references demonstrate that some mathematical facts can be demonstrated easily, given the right presentation.
I agree that there is large gap between current mathematical presentations and the optimal presentation.
I am curious how effective the optimal presentation is. How easy can we make math? We have to be careful of the trap that the 3b1b video warns us against - when we understand something it is very difficult to put yourself in the shoes of a beginner. Something that looks like an elegant and clear presentation may seem like gibberish to the beginner (look at the YouTube comments on the 3b1b video).
I tried to google "Alan kay teaching calculus smalltalk" and didn't find anything. I am curious to see how much he actually taught the kids. It's clear that the typical college student, after taking a typical calculus class, doesn't really get the point of calculus. They may be able to follow some algorithms for differentiating and integrating but I don't think they understand when they can apply calculus.
I think an important piece of the puzzle (no pun intended) is customized presentations with feedback for individually-tailored education. But then it occurs to me that group activity is also crucial for learning, eh? I'm not an expert.
Let S be a finite set of at least two points in the plane. Assume that no three points of S are collinear. By a windmill we mean a process as follows. Start with a line l going through a point P ∈ S. Rotate l clockwise around the pivot P until the line contains another point Q of S. The point Q now takes over as the new pivot. This process continues indefinitely, with the pivot always being a point from S.
Show that for a suitable P ∈ S and a suitable starting line l containing P, the resulting windmill will visit each point of S as a pivot infinitely often.
It's mainly about showcasing a problem that is objectively hard (based on IMO competition results) then revealing the simple thought process that will lead you to an "obvious" answer in a few short minutes. The main point is that there are problems where once you know the "trick", you can't accurately judge how hard the problem is anymore.
I think people would appreciate that point a lot more if they struggle with the problem for a bit first!
It is a kind of puzzle to try out on your own, knowing that a rather simple mathematical reasoning solves it. It doesn't rely on some obscure mathematical knowledge as might be suspected from an Olympiad problem.
If you want to see Grant Sanderson, instead of only hearing his voice, he uploaded a Q&A where he explains his motivations. Mainly, creating educational math videos that other people would not be able to create.
Any formal proof along those lines?