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September 27

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Uses of Pascal's tetrahedron

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The following is a use of Pascal's triangle:

To find how many ways there are to make a total of circles all black or red, the formula is just . For example, there are ways to make a group of 6 circles, all black or red, classified by whether each circle is black or red. An example is black-red-black-red-black-red.

But how about finding the number of ways to make a group of 6 circles, all black or red, classified by how many are black or red. To find out how many ways there are to make a total of circles all black or red classified by how many are black and how many are red, you use the n+1th row of Pascal's triangle. For , this means we use the seventh row, which is . This means that there is one way to color 6 circles where all of them are black, 6 where 5 are black and one is red, 15 where 4 are black and 2 are red, 20 where 3 are black and 3 are red, 15 where 2 are black and 4 are red, 6 where one is black and 5 are red, and one where all 6 are red.

How about a similar application for Pascal's tetrahedron?? Here is the seventh layer of the tetrahedron:

1
6 6
15 30 15
20 60 60 20
15 60 90 60 15
6 30 60 60 30 6
1 6 15 20 15 6 1

Just as the seventh row of Pascal's triangle can be used for the classification of ways to make 6 circles all of which are black or red classified by how many are black and how many are red, it is likewise true that the seventh layer of Pascal's tetrahedron can be used for... Georgia guy (talk) 14:06, 27 September 2024 (UTC)[reply]

It counts how many ways there are to make 6 circles all of which are black, red, or green, classified by how many are black, how many are red, and how many are green. For example, if you want there to be 2 of each colour, you get ways, which is exactly the middle entry of this layer. Double sharp (talk) 14:55, 27 September 2024 (UTC)[reply]
I would call 1, 6, 15, ... the sixth row, and the top row, with a single 1, the zeroth row. That's what Wikipedia's does in the articles I've seen at least. Anyway, this should be in the article Pascal's pyramid, and can be further extended to Pascal's simplex. The article on the Multinomial theorem is relevant here as well. --RDBury (talk) 17:25, 27 September 2024 (UTC)[reply]
RDBury, is the top row "1" not really a row?? Georgia guy (talk) 21:02, 27 September 2024 (UTC)[reply]
Well, you can call it whatever you want and index it as you like; I'm not going to get into the philosophy of rows. But the formulas are simpler if you start with the top "1" as row 0. --RDBury (talk) 00:55, 28 September 2024 (UTC)[reply]
RDBury, does that statement parallel the statement that trigonometry is simpler if you use radians as opposed to degrees?? Georgia guy (talk) 01:04, 28 September 2024 (UTC)[reply]
The OP was calling what most people call row 6 "the seventh row" and I thought that was worth pointing out for future reference. Getting caught up in what counts as a "row" and whether statements are parallel is a matter for philosophy and linguistics. --RDBury (talk) 02:20, 28 September 2024 (UTC)[reply]
@Georgia guy: Hopefully this looks more like what you intended...
             1
           6   6
         15  30  15
       20  60  60  20
     15  60  90  60  15
   6   30  60  60  30  6
 1   6   15  20  15   6   1
--CiaPan (talk) 13:32, 10 October 2024 (UTC)[reply]

September 28

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Bitcoin price rigging

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I have been day trading bitcoin for almost a year now. I read articles from bitcoin news to try and guess when the dips and dives will happen and so far it has helped. I just read and article about bitcoin possibly losing freedom to governments and large institutions being able to rig the price. This has happened recently with the German government of Saxony selling off a hoard of seized coin, The Mt. Gox dispersal, and the US dept of Justice mysteriously moving 30/230k of its seized hoard two days after Trumps bitcoin speech in Nashville raised the price. https://mpost.io/u-s-unloads-2-billion-in-bitcoin-from-silk-road-seizure/

Is it possible for a whale (large bitcoin hodler) to make smaller transactions in a short time to move the price for a larger transaction at a later time? On the upswing this is called 'pump and dump' and 'poop and scoop' on the down swing. Both are illegal in most market trades.

This post may fit better in Humanities where finance is listed or IT where crypto may belong. 2604:3D08:5E7A:6A00:D94:3638:168B:18A0 (talk) 08:38, 28 September 2024 (UTC)[reply]


I'm pretty sure that this isn't a math question. But the article on Pump and dump does explicitly mention cryptocurrencies. --RDBury (talk) 13:22, 28 September 2024 (UTC)[reply]
The reason I posted in math is because I am wondering if a small buy or sell in a quick time frame will actually move the price enough for traders like me who watch the minute candle scale. I use MetaTrader 4 where the price moves in microseconds every time a buy/sell happens. Is there a formula for volume needed to move the price in a small time frame or article about time/volume/price/ ratio calculations?
Pump and dump, Bear raid, Short and distort, and Uptick rule, all help to explain how it is possible for whales to control the price. Fear_of_missing_out#Investing is the main cause of up-spikes since I have been investing and most are followed by dives. https://www.weforum.org/agenda/2024/08/explainer-carry-trades-and-how-they-impact-global-markets/ The carry trade crash the 1st week of August caused another huge dive. Foreign_exchange_market#Carry_trade2604:3D08:5E7A:6A00:D94:3638:168B:18A0 (talk) 17:48, 28 September 2024 (UTC)[reply]
The time needed to move the needle with high-frequency trading is a combination of the latency of the connection between the computers of the flash traders and those of the exchanges, which depends on the current state of the networking technology and the physical distance between the traders and the exchange, as well as any regulations enforcing a time lag. It then will take time before small-time traders can see the needle having moved. A mathematical model will require too many parameters to be of practical use.  --Lambiam 08:51, 29 September 2024 (UTC)[reply]

September 29

[edit]

Is this a possible Groth16/ZkSnark verifier‑side simplification ?

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Hello,

The verification algorithm is already simple but I was thinking about some costly environments like blockchains having low block limits. This might be naïve thinking but I was wondering at possibility : normally the prover gives 3 elliptic curves points to the verifier A ; B ; C When public inputs are used C/the inputs vector is split.

But as a simplification part, why not completely ditch the C parts of the proof when public inputs are used ? That way, the verifier would have to compute 1 pairing in less for verifying the proof. I’m meaning e(C,verifying_key_part). It seems to me the requirement to pair with public inputs would still ensure the security of the system… Is it because skipping that pairing would allow to forge public inputs ? As far I understand, a malicious prover would still have to satisfy all constraints of the quadratic arithmetic program and thus would have to use public inputs satisfying constraints. Or is it because it would be impossible to rework the protocol to have the prover being able to produce proofs that verify ?

Or even maybe both of the assumptions above ? 2A01:E0A:401:A7C0:9CB:33F3:E8EB:8A5D (talk) 11:51, 29 September 2024 (UTC)[reply]

September 30

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How to find max(xy) for each r where x + y = r and x, y are positive integers

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Drawing fractal canopy diagrams had me wondering for a given SVG file size, I could add more branches or more depth. Below are two examples:

2 branches, depth 12
4 branches, depth 8

To make the tree as dense as possible, I wish to maximise the number of leaf nodes. In other words, how can I find max(xy) for each r where x + y = r and x, y are positive integers?

I realise I can use calculus but I'm unsure what equation I should differentiate.

Thanks, cmɢʟeeτaʟκ 00:50, 30 September 2024 (UTC)[reply]

Unfortunately, this is actually quite complicated. We can rewrite the problem as , and consider all real instead of just integers. Notice that . Because is monotonic over , is maximized when is. Its derivative is , which is when . This is a nice closed-form expression, but it's for in terms of . Inverting it is complicated, but Wolfram Alpha gives us where is the Lambert W function. While this is sort of a closed-form expression, it's still unfortunately annoying to work with since is implicitly defined as . In any case, is irrational for all positive rational . The proof of this is annoying so I've put it below, but ultimately what it implies is that when , as far as I can tell, the best you can do is either round for convenience, or take floor/ceiling of and compare values to get the max over integers.
Proof that is irrational for positive rational
  1. Suppose , and let .
  2. and , so as well.
  3. By definition, . Since , we can rearrange to get .
  4. Lindemann's 1882 theorem implies that if is nonzero rational, then is not only irrational, but transcendental as well.
  5. If is rational, then since , is transcendental, while is rational, which is contradictory.
  6. must be irrational and is nonzero, so is irrational.
  7. We conclude that implies is irrational.
GalacticShoe (talk) 02:41, 30 September 2024 (UTC)[reply]
Here is a numerical recipe (Newton's method) for solving for real-valued :
  1. Set
  2. Iterate the replacement until convergence, where
In practice (), two iterations will bring you close enough; then test and to get the optimal integer value.  --Lambiam 10:17, 30 September 2024 (UTC)[reply]
Thanks so much, @GalacticShoe and @Lambiam. I thought analytically I was heading into a dead end. Guess solving it iteratively is still the best for small values. cmɢʟeeτaʟκ 11:45, 30 September 2024 (UTC)[reply]
P.S. It seems there's an interesting trend:
x=1 for r=2 (1 term): 1¹.
x=2 for r=3 to 4 (2 terms): 2¹ and 2².
x=3 for r=5 to 7 (3 terms): 3², 3³ and 3⁴.
x=4 for r=8 to 11 (4 terms): 4⁴, 4⁵, 4⁶ and 4⁷.
x changes when r is the x–1th triangular number + 2. Serendipity? cmɢʟeeτaʟκ 17:06, 30 September 2024 (UTC)[reply]
Unfortunately, serendipity. The number of for each is the sequence OEIS:A108414. Although it starts with , it quickly levels out. The inverse triangular number function you're looking for is , while grows faster than , which in turn grows faster than , hence the number of terms slowing down in growth. GalacticShoe (talk) 03:46, 1 October 2024 (UTC)[reply]
Note that, unlike for Tn, these first differences in the r-values for which x changes do not only always increase but may even decrease.  --Lambiam 03:58, 1 October 2024 (UTC)[reply]
After some testing, it seems that rounding suffices at least for r < 100, possibly more. To simplify it, applying Newton's method twice, we can get this approximation which maximizes for these values of :
GalacticShoe (talk) 04:14, 1 October 2024 (UTC)[reply]
Thanks so much, @Lambiam and @GalacticShoe. I much appreciate the time and effort you've put into it. Cheers, cmɢʟeeτaʟκ 20:17, 2 October 2024 (UTC)[reply]


October 3

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Prime Pythagorean triples

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Are there infinitely many Pythagorean triples where both of a and c are prime?? (Using the rule that a is always the short leg and b is the long leg, I conjecture [please disprove me if possible] that there are no Pythagorean triples where b is prime.)

Properties:

  • c-b is always 1.
  • Except in the case of 3,4,5, and 5,12,13 b is always a multiple of 60.

Georgia guy (talk) 23:38, 3 October 2024 (UTC)[reply]

The formula for Pythagorean triples, assuming the numbers are relatively prime, is p=x2-y2, q=2xy, r=x2+y2, where x>y>0, x and y are relatively prime, and x and y are not both odd. Your a and b are p and q, possibly in a different order, and your c is r. Suppose b is prime. Then b cannot be q since q is even, so b is p and p > q. Further, x-y is a factor of p, and since p is prime, x-y = 1. So we get p = 2y+1, q=2y(y+1). Then p>q implies 2y2-1 < 0, which is impossible for y>0. As a further result of this proof, the only Pythagorean triples with a prime side are of the from 2y+1, 2y(y+1), 2y2+2y+1, which includes the 3, 4, 5 and 5, 12, 13 examples. It also generates at least a few more: 11, 60, 61; 19, 180, 181; 29, 420, 421. I think you're right about b being a multiple of 60; I haven't written out a proof, but I don't expect it would be that difficult. I suspect there are infinitely many triples where a and c are prime. This amounts to saying there are infinitely many primes p so that (p2+1)/2 is also prime. Statements like this are usually difficult to prove though. For example it's unknown if there are infinitely many primes p such that p+2 is prime. Unless there is a congruence or set of congruences, or a polynomial factorization which can prove it easily then the likelihood is that it's extremely difficult; there's seldom a middle ground. --RDBury (talk) 04:23, 4 October 2024 (UTC)[reply]
For al such triples with 5 < p < 100000, q ≡ 0 (mod 60).  --Lambiam 07:55, 4 October 2024 (UTC)[reply]
It is easily seen that (q mod 60) = 0 iff (y mod 15) ∈ {0, 5, 9, 14}. In each of the 11 other cases, by elementary modular arithmetic, at least one of p and r is divisible by at least one of 3 and 5. This includes the two triples (3, 4, 5) and (5, 12, 13).  --Lambiam 08:24, 4 October 2024 (UTC)[reply]
A somewhat more interesting issue is the divisibility properties of p, q and r when they aren't restricted to primes. That q is divisible by 4 is trivial. Either p or q is divisible by 3 (but not both) is seen by considering the 9 pairs of remainders of x and y mod 3. The x%3=y%3=0 is eliminated because x and y are assumed relatively prime. With a similar case breakdown, either p, q or r is divisible by 5. So if neither p or r are divisible by 3 or 5, then q is divisible by 60. This idea breaks down for divisibility by 7, but one can say that r is never divisible by 7, nor by any other prime s with s%4=3. --RDBury (talk) 13:31, 4 October 2024 (UTC)[reply]
For reference, the OEIS sequence of hypotenuses for such triples is OEIS:A067756. GalacticShoe (talk) 13:57, 4 October 2024 (UTC)[reply]





October 12

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