Search found 861 matches

by LucasBrown
Wed Apr 12, 2017 5:52 am UTC
Forum: The Help Desk
Topic: Issues with opengl / webgl on Ubuntu 16.04 MATE
Replies: 1
Views: 835

Issues with opengl / webgl on Ubuntu 16.04 MATE

System info: ⋅  Ubuntu 16.04.2 LTS (Xenial) 64-bit ⋅  Kernel 4.4.0-47-generic x86_64 ⋅  MATE 1.12.1 ⋅  Intel i7-6700K ⋅  64 GB RAM ⋅  GeForce GT 730 ⋅  NVIDIA binary driver version 375.39 Some time ago (a few weeks to a couple mon...
by LucasBrown
Sat Apr 01, 2017 7:31 pm UTC
Forum: Mathematics
Topic: Odd cubic perfect numbers divisible by 5
Replies: 0
Views: 730

Odd cubic perfect numbers divisible by 5

Have they been shown to be nonexistent? I know that the existence of odd perfect numbers is an open question, and I also know that so many constraints have been derived on them that they probably don't exist, but I'm presently concerned only with those that are also cubes and multiples of 5. This ar...
by LucasBrown
Sun Oct 23, 2016 9:51 am UTC
Forum: Coding
Topic: Where to find interview-style coding problems?
Replies: 8
Views: 2056

Re: Where to find interview-style coding problems?

Programming Praxis posts interview questions every now and then.
by LucasBrown
Tue Oct 04, 2016 4:36 am UTC
Forum: Science
Topic: Ideal lenses
Replies: 0
Views: 3472

Ideal lenses

TL;DR: What is the shape of the ideal planoconvex lens? More precise formulation, and my work so far: A lens sits in the xy plane. The lens has index of refraction n 2 and the rest of the plane has index of refraction n 1 . The lens is bounded below by the x axis and above by a function f ( x ). Le...
by LucasBrown
Mon Oct 03, 2016 2:04 pm UTC
Forum: Mathematics
Topic: Factorization using modular arithmetic
Replies: 41
Views: 5382

Re: Factorization using modular arithmetic

Solving quadratic equations modulo composites is indeed easy when the modulus is small, but when the modulus is large, the best methods we know of involve actually factoring the modulus. So unless you have a fast way to solve modular quadratics that doesn't involve factoring, this isn't going anywhe...
by LucasBrown
Thu Sep 08, 2016 3:52 am UTC
Forum: Mathematics
Topic: What's your favourite irrational number?
Replies: 78
Views: 17438

Re: What's your favourite irrational number?

Eebster the Great wrote:What about the number x defined such that 0 < x < 1 and the ith digit of x is the ith element of 0 (mod 10), ordered lexicographically, where 0 is zero dagger?


The problem with that is that it might not exist.
by LucasBrown
Wed Aug 31, 2016 11:00 am UTC
Forum: Science
Topic: What is the largest possible artificial lake we could make today?
Replies: 16
Views: 2134

Re: What is the largest possible artificial lake we could make today?

We can avoid the issues presented by dams by simply flooding a pre-existing endorheic basin. In fact, we've already done this by accidentally creating the Salton Sea . The Salton Sea is currently 73m below sea level; to raise it to 0m, we could just dig a canal from the ocean to the New River or Ala...
by LucasBrown
Wed Aug 31, 2016 10:37 am UTC
Forum: Mathematics
Topic: Torsion subgroups for elliptic curves over Q
Replies: 3
Views: 1444

Re: Torsion subgroups for elliptic curves over Q

Computing 12P directly is quite inefficient when P isn't a torsion point: for non-torsion points, the denominators of nP are about twice the size (in terms of bit length) of the denominators of (n-1)P, which slows down the computation dramatically. So it's much more efficient for non-torsion points ...
by LucasBrown
Mon Aug 29, 2016 9:56 am UTC
Forum: Mathematics
Topic: Torsion subgroups for elliptic curves over Q
Replies: 3
Views: 1444

Torsion subgroups for elliptic curves over Q

TL;DR : Is there a way faster than the Nagell-Lutz theorem to tell whether the torsion subgroup of the elliptic curve y 2 = x 3 + ax + b over Q , where a and b are integers, is trivial? Context: As a personal project I wrote some code to analyze an elliptic curve over the rationals to extract and c...
by LucasBrown
Wed Aug 24, 2016 12:24 pm UTC
Forum: Individual XKCD Comic Threads
Topic: 0827: "My Business Idea"
Replies: 98
Views: 20166

Re: 0827: "Business Idea"

OP here. 'Tis changed.
by LucasBrown
Wed Aug 03, 2016 1:02 pm UTC
Forum: Computer Science
Topic: How good is lattice based cryptography looking?
Replies: 1
Views: 1615

Re: How good is lattice based cryptography looking?

I have no answer for this, but I'd like to quasi-hijack this thread to ask the corresponding question about cryptography based on supersingular isogeny.
by LucasBrown
Thu Jun 23, 2016 1:46 am UTC
Forum: Forum Games
Topic: Count up with the Five Fives puzzle
Replies: 298
Views: 11303

Re: Count up with the Five Fives puzzle

27=5*5+((5+5)/5)
by LucasBrown
Wed Jun 15, 2016 6:02 pm UTC
Forum: Mathematics
Topic: Completions, Cauchy sequences, and countability
Replies: 7
Views: 2347

Re: Completions, Cauchy sequences, and countability

If it's just decimals that you don't like, then I recommend using continued fractions instead. There is a 1-to-1 correspondence between infinite simple continued fractions and irrational numbers: each infinite SCF converges to a single value, and each irrational number has a unique SCF that represen...
by LucasBrown
Wed Jun 08, 2016 11:50 pm UTC
Forum: Coding
Topic: Memoizing a generator in Python
Replies: 1
Views: 2212

Memoizing a generator in Python

I'd like to memoize a generator in Python. Specifically, I have an incremental sieve of Eratosthenes that gets called from scratch a lot , and I'd like to avoid recomputing (up to some arbitrary finite number of) the numbers it yields. Memoizing a pure function is easy enough, and there are any numb...
by LucasBrown
Thu Jun 02, 2016 2:01 am UTC
Forum: Forum Games
Topic: Can you produce [X] in less than 15 seconds?
Replies: 6776
Views: 413339

Re: Can you produce [X] in less than 15 seconds?

There is one within 15 seconds' distance from me, but actually finding it in that pile of junk took too long.

A pressure vessel of any sort?
by LucasBrown
Tue May 31, 2016 4:59 pm UTC
Forum: Forum Games
Topic: Can you produce [X] in less than 15 seconds?
Replies: 6776
Views: 413339

Re: Can you produce [X] in less than 15 seconds?

Took me more than 15 seconds to decide which one was the best, but all my options were within 15 seconds of me, so yes.

Copper that isn't part of a coin or electrical device?
by LucasBrown
Sun May 29, 2016 11:12 am UTC
Forum: Forum Games
Topic: Can you produce [X] in less than 15 seconds?
Replies: 6776
Views: 413339

Re: Can you produce [X] in less than 15 seconds?

Nope. Never even heard of such a feature.

In other news, I have several pounds of tungsten sitting on my desk.
by LucasBrown
Sun May 29, 2016 11:10 am UTC
Forum: Forum Games
Topic: Complete the Grid!
Replies: 1232
Views: 87652

Re: Complete the Grid!

E3
by LucasBrown
Sun May 15, 2016 2:50 am UTC
Forum: Forum Games
Topic: Complete the Grid!
Replies: 1232
Views: 87652

Re: Complete the Grid!

F3
by LucasBrown
Sun May 15, 2016 2:37 am UTC
Forum: Forum Games
Topic: The Incredible Changing Sentence
Replies: 5612
Views: 480219

Re: The Incredible Changing Sentence

Christian canonized caramel chameleons' circadian Circassian Kardashians' Cardassians' Dame Rapunzel Č. McGuirewa's not the Empress who wished for so much purple omorashi that my platinum clock and the moribund pancake mandrake then creates plans, definitely Dirty... so why not Marxism?
by LucasBrown
Wed May 11, 2016 5:13 am UTC
Forum: Forum Games
Topic: Complete the Grid!
Replies: 1232
Views: 87652

Re: Complete the Grid!

I reflected the rainbow in F5.
by LucasBrown
Wed May 11, 2016 5:03 am UTC
Forum: Forum Games
Topic: The Incredible Changing Sentence
Replies: 5612
Views: 480219

Re: The Incredible Changing Sentence

Of chameleons' circadian Circassian Kardashians' Cardassians, Rapunzel Č. McGuire was not convinced, but Empress Violentlyyeti, viewing my platinum clock, and the slimy pancake I then create, is definitely Dirty Beatrix Potter.
by LucasBrown
Sun May 08, 2016 7:51 pm UTC
Forum: Coding
Topic: [Resolved] Generalized Hamming numbers in Python
Replies: 3
Views: 2500

Re: [Resolved] Generalized Hamming numbers in Python

Thanks; that was enlightening.
by LucasBrown
Sat May 07, 2016 8:04 pm UTC
Forum: Coding
Topic: [Resolved] Generalized Hamming numbers in Python
Replies: 3
Views: 2500

[Resolved] Generalized Hamming numbers in Python

I found an elegant and efficient Hamming number generator in Python, which I have modified a bit to fit my own personal idiom: from itertools import tee, chain, groupby from heapq import merge def hamming0(): def deferred_output(): yield from output p2, p3, p5, result = tee(deferred_output(), 4) m2,...
by LucasBrown
Wed Apr 06, 2016 6:42 pm UTC
Forum: Mathematics
Topic: Efficiently summing a multiplicative function via inclusion-exclusion
Replies: 3
Views: 1599

Re: Efficiently summing a multiplicative function via inclusion-exclusion

Because the folks running the challenge discourage participants from posting full solutions on their blogs or finding the solutions by googling for people who do post their solutions like that. From their FAQ: I solved it by using a search engine, does that matter? Making use of the internet to rese...
by LucasBrown
Tue Apr 05, 2016 7:11 pm UTC
Forum: Mathematics
Topic: Efficiently summing a multiplicative function via inclusion-exclusion
Replies: 3
Views: 1599

Efficiently summing a multiplicative function via inclusion-exclusion

This might be better suited to the Coding or CS sections, but this seems mathy enough to belong here. I'm working on a problem for a programming challenge (obfuscated to make googling this thread harder: it's # 22 2 in rot13(Cebwrpg Rhyre)). It devolves to computing the sum of a multiplicative funct...
by LucasBrown
Fri Mar 04, 2016 5:51 pm UTC
Forum: Mathematics
Topic: Cardano triplets
Replies: 0
Views: 3212

Cardano triplets

Project Euler problem #251 defines a Cardano triplet as a triplet of positive integers ( a , b , c ) such that ∛( a + b √ c ) + ∛( a - b √ c ) = 1. We are asked to find the number of Cardano triplets with a + b + c ≤ 110,000,000. There's a reasonably obvious solution (transform the equation to b 2 ...
by LucasBrown
Wed Feb 24, 2016 2:03 am UTC
Forum: Science
Topic: Food pressure
Replies: 3
Views: 1968

Re: Food pressure

Soooo.... convert the chemical potential energy of that cantaloupe into heat but keep it in the same volume, and you'd have a gas with 109 Pa of pressure?
by LucasBrown
Sat Feb 13, 2016 3:57 am UTC
Forum: Mathematics
Topic: Initial seeds for Aberth's method
Replies: 1
Views: 1203

Initial seeds for Aberth's method

When using Aberth's method for approximation of polynomial roots, are there any restrictions on the values of the initial seeds? Various root-finding methods are known to fail when the initial seeds are ill-conditioned in some manner (such as Durand-Kerner's inability to find non-real roots when the...
by LucasBrown
Tue Jan 19, 2016 3:28 am UTC
Forum: Coding
Topic: xkcd Phone: Application Programming Language
Replies: 21
Views: 5793

Re: xkcd Phone: Application Programming Language

There will be no such thing as indentation. Lines beginning with whitespace produce syntax errors.
by LucasBrown
Wed Jan 06, 2016 1:57 am UTC
Forum: Mathematics
Topic: Elementary evaluation of Legendre symbol (3|p)
Replies: 2
Views: 1152

Re: Elementary evaluation of Legendre symbol (3|p)

Huh...

Thanks, that was helpful.
by LucasBrown
Tue Jan 05, 2016 3:43 am UTC
Forum: Mathematics
Topic: Elementary evaluation of Legendre symbol (3|p)
Replies: 2
Views: 1152

Elementary evaluation of Legendre symbol (3|p)

Using Euler's criterion and quadratic reciprocity, it can be shown with little difficulty that for odd primes p ≥5, we have 3 ( p -1)/2 ≡(-1) ⌊(p+1)/6⌋ (mod p ), which then reduces further to +1 if p ≡±1 (mod 12) and -1 if p ≡±5 (mod 12). I'd like to prove this in a more elementary f...
by LucasBrown
Sat Dec 26, 2015 6:04 pm UTC
Forum: Mathematics
Topic: Counting tetris arrangements
Replies: 2
Views: 1220

Re: Counting tetris arrangements

The shifted version you describe would not be considered stable.
by LucasBrown
Sat Dec 26, 2015 1:47 am UTC
Forum: Mathematics
Topic: Counting tetris arrangements
Replies: 2
Views: 1220

Counting tetris arrangements

So I received this lamp for xmas... https://www.thinkgeek.com/images/products/zoom/f034_tetris_stackable_LED_desk_lamp.jpg It consists of the seven Tetris pieces; the long one plugs into the wall, and the other pieces can be pushed up against it to light up. Their arrangement must be coplanar, and t...
by LucasBrown
Thu Dec 17, 2015 3:36 am UTC
Forum: Science
Topic: Wendelstein 7-X
Replies: 43
Views: 5592

Re: Wendelstein 7-X

If the helium and the neutron carry equal kinetic energies, then their momenta will have different magnitudes.
by LucasBrown
Tue Dec 15, 2015 3:49 am UTC
Forum: Science
Topic: Unbihexium density?
Replies: 11
Views: 2066

Re: Unbihexium density?

Incidentally, where did you get tungsten in that purity / shape? I've been looking for some in a spherish sort of form with a purity in the range of 99%, but all I can find is ultra-expensive precision-machined stuff.
by LucasBrown
Sat Nov 28, 2015 8:12 pm UTC
Forum: Mathematics
Topic: Record High/Low
Replies: 3
Views: 1231

Re: Record High/Low

But if the distribution shifts, then the probability of a record is increased in the direction of the shift, with the net result being an increase in the total number of records — for example, the planet is warming up, so we can expect (and in fact we do observe) an excess of record highs and a dear...
by LucasBrown
Mon Nov 16, 2015 7:13 pm UTC
Forum: Forum Games
Topic: Count to a Million
Replies: 71281
Views: 3638301

Re: Count to a Million

2 × 3 × 29 × 359
by LucasBrown
Fri Oct 02, 2015 12:08 am UTC
Forum: Mathematics
Topic: Factoring numbers of the form p^x+q^y
Replies: 3
Views: 1673

Re: Factoring numbers of the form p^x+q^y

If both exponents are powers of 2, then we're looking at generalized Fermat numbers . If p=y and x=q , we have ourselves a Leyland number . If both exponents are 4, we're dealing with quartan numbers . I am not aware of any term that encompasses all numbers of the form you're discussing, so I'll ana...
by LucasBrown
Mon Jun 22, 2015 2:41 am UTC
Forum: Coding
Topic: Happy bases
Replies: 12
Views: 2772

Re: Happy bases

That appears to be correct, but it's been several years since since I (briefly) studied quadratic fields, so I wouldn't go so far as to give it my seal of approval.

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