Live data from Hacker News

A Strange Grid Reveals Hidden Connections Between Simple Numbers

quantamagazine.org

31–40 of 40 posts

Re: A Strange Grid Reveals Hidden Connections Between Simple Numbers

#31

Earlier quoted context omitted.

This is maths we are talking about, you should never assume that the common usage of words applies to the precise definition used in the maths context. Take the Boolean inclusive "or", for example.

I think people that know 'product', 'geometric series', etc. know what distinct means. It doesn't have some special mathematical meaning here.

Sure, but this is not an article aimed at those people. Note that geometric progression is also defined later on.

Re: A Strange Grid Reveals Hidden Connections Between Simple Numbers

#32
post #11

My intuition was already screaming 'it'll be the other way around for a geometric progression' before I read that far, but I'm damned if I can understand or even speculate why. Most likely I don't properly understand it. I'm inclined to wonder if there's a third operator which could be tested like this, such as exponentiation, but that's not commutative over integers. Of course, if there are similarly intriguing patt…

> My intuition was already screaming 'it'll be the other way around for a geometric progression' before I read that far, but I'm damned if I can understand or even speculate why.

It's a question of forcing the number of sums/products to be low. An arithmetic progression forces a large number of identical sums for the obvious reason: (a+b) = ((a-k)+(b+k)) = ((a-2k) + (b+2k)), and so on, and those differences of k are... the definition of an arithmetic progression.

The reason a geometric progression produces a lot of identical products is exactly the same. (ab) = (a/k · bk) = (a/kk · bkk)...

Re: A Strange Grid Reveals Hidden Connections Between Simple Numbers

#33
I studied applied mathematics but I have to admit number theory has always been, and probably always will be, a total mystery to me. My whole intuition is tied to dynamics and computability, and this is just absolutely alien. I’m probably more in awe of number theorists than the average person because whereas they group them with mysterious ‘mathematicians’ (with all their attendant mystique and implied genius) I’ve actually “been there, [tried] to do that” and failed, and that marks it out as an almost insurmountable peak.

Re: A Strange Grid Reveals Hidden Connections Between Simple Numbers

#34
post #19
post #8

i dont get it...what is the hidden connection exactly?

The real point is that no one gets the hidden connection. There are lots of tantalizing clues in number theory that lead us to believe there is some fundamental connection between addition and subtraction but we can't state it outright. This toy problem is like a black box in that we can play with it and quantify it's behavior but we don't know (exactly) why it works.

I think you mean “addition and multiplication”, not “multiplication and subtraction”... there definitely is a lot of evidence that addition and subtraction are related, but that’s just plain trivial.

Re: A Strange Grid Reveals Hidden Connections Between Simple Numbers

#35
post #7

Earlier quoted context omitted.

”but it seems obvious that a multiplicative table will result in more 'numerical diversity' than a summation table” That isn’t true. If you pick the set of numbers {1, 2, 4, 8} , you get 10 different sums (2, 3, 4, 5, 6, 8, 9, 10, 12, and 16) but only 7 different products (1, 2, 4, 8, 16, 32, and 64)

Sure, you can always find special-case exceptions, but I still don't see why the result is surprising in the general case. There are a lot more arithmetic progressions than geometric ones.

Ah but the conjecture isn't about what happens “on average” or for a “random set” of integers. It's about what is forced to happen in every possible case. (In the “random” case there are probably very few or no duplicates anyway, as both a+b=c+d and ab=cd will be unlikely for completely random integers — note that they say d is exactly a+b-c or ab/c respectively — the conjecture is about limiting what you could possibly arrange to happen, non-randomly.)

Basically, when you take integers like {1, 2, 3, 4} or {1, 3, 5, 7} (so that there are additive relations between them) (e.g. small integers), there tends to be a lot of duplicates in the addition table. But if you take integers like {1, 2, 4, 8} or {1, 3, 9, 27} (so that there are multiplicative relations between them) (e.g. very similar prime factorizations), there tend to be a lot of duplicates in the multiplication table. In other words, it's very easy to create sets with either lots of duplicates in the addition table or lots of duplicates in the multiplication table.

The conjecture is not about which kind of set is more common (so it doesn't matter even if it's true that there are a lot “more” arithmetic progressions than geometric ones, in whatever sense), but rather says there is no way you can create a set with both sorts of collisions — it's saying that if a set has many additive coincidences it can't have many multiplicative coincidences and vice-versa.

Re: A Strange Grid Reveals Hidden Connections Between Simple Numbers

#37
post #34
post #19

Earlier quoted context omitted.

The real point is that no one gets the hidden connection. There are lots of tantalizing clues in number theory that lead us to believe there is some fundamental connection between addition and subtraction but we can't state it outright. This toy problem is like a black box in that we can play with it and quantify it's behavior but we don't know (exactly) why it works.

I think you mean “addition and multiplication”, not “multiplication and subtraction”... there definitely is a lot of evidence that addition and subtraction are related, but that’s just plain trivial.

Thank you, mobile commenting is a blessing and a curse.

Re: A Strange Grid Reveals Hidden Connections Between Simple Numbers

#38

Earlier quoted context omitted.

> There are a lot more arithmetic progressions than geometric ones. I'm pretty sure that's not true. An arithmetic progression is x[n] = x[n-1] + k and a geometric progression is x[n] = x[n-1] * k

That's a good point, I'll have to stand corrected on that. Just a matter of swapping one operation for another.

If you consider all finite sequences of positive integers with all values below some limit M, it might be the case that there are more arithmetic sequences than geometric sequences. I don't think that's relevant to the article, but might be where your head was when you made that post.

Re: A Strange Grid Reveals Hidden Connections Between Simple Numbers

#40
post #37
post #34

Earlier quoted context omitted.

I think you mean “addition and multiplication”, not “multiplication and subtraction”... there definitely is a lot of evidence that addition and subtraction are related, but that’s just plain trivial.

Thank you, mobile commenting is a blessing and a curse.

Heh, no worries. I got it wrong too... I meant to write “addition and subtraction” and ended up writing “subtraction and multiplication”... so that’s what I get for trying to be a pedant (and boy do I deserve it).
Post reply on HN