That problem is actually very easy to solve. If you number the cells in binary, patterns fall out enough that it's easy to convert back and forth from the original numbering to the final numbering. If he wants to just work it out by hand, well, maybe he doesn't understand math as well as he thinks. If you want to use math to "build hammers", it help to know what a nail is first.
There are no rules in math
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Re: There are no rules in math
#12That problem is actually very easy to solve. If you number the cells in binary, patterns fall out enough that it's easy to convert back and forth from the original numbering to the final numbering. If he wants to just work it out by hand, well, maybe he doesn't understand math as well as he thinks. If you want to use math to "build hammers", it help to know what a nail is first.
Suppose we are interested in the function f(N) such that a cell which originally has N squares to its left ends up with f(N) squares under it.
To calculate f(N), write N out in binary with K + 1 bits [where the tape has 2^K squares], including a leading zero. Reverse this bitstring [exchanging most- and least-significant bits, etc.]. Finally, if the result has a leading one rather than a leading zero [i.e., if N was odd], flip all the bits [turning ones into zeros and vice versa]; otherwise, leave them be. This yields the binary description of f(N) [with K + 1 bits, including a leading zero].
In the given example, N is 941; i.e., 01110101101, using ten + 1 binary bits. Reversing this, we get 10110101110. Finally, since this has a leading one, we flip all the bits to get 01001010001. This the binary description of 593, which is the answer.
(More generally, suppose at some point in the process, the tape has been folded to a width of 2^K * W squares and height of H squares, and we are interested in where the W-width, H-height block with N such blocks to its left ends up once we've gone through K more foldings to bring the tape width down to W and tape height up to 2^K * H. This block will end up with f(N) such blocks below it; if N is even, the block will be in the same orientation as currently, while if N is odd, it will be reversed 180 degrees from its current orientation (with its current top-left square becoming its bottom-right square, etc.))
Re: There are no rules in math
#13Having earned an undergraduate degree in math I've often had similar thoughts about US elementary math education's emphasis on rules and mechanical calculation and memorization rather than more abstract concepts like pattern matching. Turns out there was a thing called "New Math" ( https://en.wikipedia.org/wiki/New_Math ) in the 1960s where public elementary schools tried to teach concepts from set theory and abstrac…
Re: There are no rules in math
#14Re: There are no rules in math
#15Earlier quoted context omitted.
I was taught the "New Math" as a child and did not hate it. It was wonderful. When I look at math blogs today, they use notation and terminology I learned back then. This is a tremendous advantage (or so it seems to me).
And everyone else just curses when they open a Wikipedia article for smth that is supposedly (and actually) not that complex, but is explained in those terms, still :)
Wikipedia should be a resource for the average layman, not mathematically mature individuals who comprise the minority.
Re: There are no rules in math
#16But is there a reason why the maintainer of this blog hasn't shared his or her identity? I am very interested in your background. It looks like some of your earlier entries were made when you were in high school. In any case I am very impressed. Sent a few of your articles to my younger siblings to read.
Re: There are no rules in math
#17First off cool blog. But is there a reason why the maintainer of this blog hasn't shared his or her identity? I am very interested in your background. It looks like some of your earlier entries were made when you were in high school. In any case I am very impressed. Sent a few of your articles to my younger siblings to read.
I'm hesitant to tie my writing to a "real-life" identity because you get a lot of freedom when you dissociate yourself from what you publish. If I knew my friends/parents/potential-employers could find my blog, I would be much more hesitant to publish, which would have been very unhealthy in the long run.
Re: There are no rules in math
#18First off cool blog. But is there a reason why the maintainer of this blog hasn't shared his or her identity? I am very interested in your background. It looks like some of your earlier entries were made when you were in high school. In any case I am very impressed. Sent a few of your articles to my younger siblings to read.
Thanks! I'm actually still in high school. Shoot me an email or find me on IRC if you'd like to talk—I'd be happy to say hi. I'm hesitant to tie my writing to a "real-life" identity because you get a lot of freedom when you dissociate yourself from what you publish. If I knew my friends/parents/potential-employers could find my blog, I would be much more hesitant to publish, which would have been very unhealthy in th…
But all your posts are brilliant and I personally think you are doing yourself a disservice not putting your name out there. Like I said, I am very very impressed with the entries.
Re: There are no rules in math
#19Having earned an undergraduate degree in math I've often had similar thoughts about US elementary math education's emphasis on rules and mechanical calculation and memorization rather than more abstract concepts like pattern matching. Turns out there was a thing called "New Math" ( https://en.wikipedia.org/wiki/New_Math ) in the 1960s where public elementary schools tried to teach concepts from set theory and abstrac…
Also, like every other reform, it suffered because math illiterate parents (who know basic by rote by more) didn't understand their kids' curriculum.
Students with high aptitude (including many here on HN) thrived in New Math and became among the highest achievers in adult mathematical activity.
Re: There are no rules in math
#20My high school math teacher used to give us extra classes that weren't directly connected to the curriculum. They were always about structure, elegance, and beauty. Quite a lot of time was also spent on history: who was studying what, when, and why. (Also there was a cult of Leonard Euler, which maybe is not so surprising if you did high school math.) I found it to be the most important glue in my math education. In…