@davidradcliffe@mathstodon.xyz
@davidradcliffe@mathstodon.xyz avatar

davidradcliffe

@davidradcliffe@mathstodon.xyz

Mathematician, software developer, engineer, SJW. Co-founder of GogyUp (gogyup.com). Formerly on Twitter as @daveinstpaul.

This profile is from a federated server and may be incomplete. Browse more on the original instance.

ColinTheMathmo, to random
@ColinTheMathmo@mathstodon.xyz avatar

'Jail' and 'Prison' are synonyms. But 'Jailer' and 'Prisoner' are antonyms.

davidradcliffe,
@davidradcliffe@mathstodon.xyz avatar

@ColinTheMathmo @iris
I first became aware of the distinction between jail and prison from song lyrics by The Hold Steady (Chill Out).

"He was rough around the edges, he'd been to school but never finished
He'd been to jail but never prison"

davidradcliffe, to random
@davidradcliffe@mathstodon.xyz avatar

A friend spotted this unusual irregular tiling at an airport. Does it have a name or any interesting properties?

davidradcliffe, to random
@davidradcliffe@mathstodon.xyz avatar

I want to render this symbol as accurately as possible in LaTeX. I tried \ll but it doesn't look right. Any suggestions?

ColinTheMathmo, (edited ) to random
@ColinTheMathmo@mathstodon.xyz avatar

This must be a solved problem ...

A group I'm in is reviewing and revising a document. It's a word document, because some of them are seriously, seriously technically challenged, and that seems to be the only thing they can cope with.

But making comments on and passing copies around of a Word document is just a completely nightmare, and it ends up ... as you will all know ... a mess of formatting, wrong versions, just ... urgh.

If there is a website with the document visible and little boxes spread throughout into which people can type comments to be collected and collated, that would be much easier.

Is there such a thing?

davidradcliffe,
@davidradcliffe@mathstodon.xyz avatar

@ColinTheMathmo I think that Microsoft 365 would let you do something like that. https://support.microsoft.com/en-us/office/collaborate-on-word-documents-with-real-time-co-authoring-7dd3040c-3f30-4fdd-bab0-8586492a1f1d#:~:text=Select%20Edit%20Document%20%3E%20Edit%20in,the%20top%20of%20the%20window.

kdund, to math

A startling seeming correspondence:
Given a constant K, the probability for a normal gaussian variable to be between -K and K is the same as the probability for the minimum of two normal gaussian variables to be in that same interval !?!

davidradcliffe,
@davidradcliffe@mathstodon.xyz avatar

@kdund Cool! This seems to work for any distribution that is symmetric about 0.

davidradcliffe,
@davidradcliffe@mathstodon.xyz avatar

@kdund Because of an algebraic coincidence: (1-p)^2 - p^2 = (1 - p) - p.

ColinTheMathmo, to random
@ColinTheMathmo@mathstodon.xyz avatar

Here's a great problem from Donald Bell ... can you solve it?

========

Rectangling the Square:

Is there a set of rectangles, with no repeated length of side, that will tile more than one rectangle?

========

To get the context of the problem you'll need to read Donald's DOCX ... I'm not really in a position to extract and reformat it, but I'm hosting a copy here:

http://www.solipsys.co.uk/documents/DonaldBell_RectanglingTheSquare.docx

Love to hear your ideas !!

(Boosts welcome for reach)

davidradcliffe, (edited )
@davidradcliffe@mathstodon.xyz avatar

@ColinTheMathmo

davidradcliffe,
@davidradcliffe@mathstodon.xyz avatar

@ColinTheMathmo I picked a topology for the subdivisions, and then I wrote a Python script to search for solutions. I found another solution with minimum side length 2.

davidradcliffe,
@davidradcliffe@mathstodon.xyz avatar

@ColinTheMathmo Maybe next year!

davidradcliffe,
@davidradcliffe@mathstodon.xyz avatar

@ColinTheMathmo Here's a solution that doesn't require rotating the smaller rectangles. The dimensions of the larger rectangles are 35×20 and 28×25, respectively.

davidradcliffe,
@davidradcliffe@mathstodon.xyz avatar

@ColinTheMathmo @donaldbell It's a nice question. Once you know one solution, it's straightforward to find infinitely many by solving an underdetermined system of linear equations.

davidradcliffe, to random
@davidradcliffe@mathstodon.xyz avatar

I'm still trying to fully understand Shor's quantum algorithm for factoring integers, and why the inverse QFT is needed.

Here's my thinking. If (a,N)=1 then there is a unitary U, defined such that U|x> = |ax> for (x,N)=1 and U|x| = |x> otherwise. The eigenvalues of U are the d-th roots of 1, where d is the multiplicative order of a modulo N. If we could compute a nontrivial eigenvalue of U, then we could use it to compute d, and then factor N.

So, my naive question is this. What are the obstacles to computing the eigenvalues of U directly? (I'm not even sure what "directly" would mean in the context of a quantum algorithm.)

davidradcliffe, to random
@davidradcliffe@mathstodon.xyz avatar

This is a transformer near my home, bearing the number 2537. The digits consist of the first four primes (out of order), but the number is composite. Can you factor it mentally?

davidradcliffe,
@davidradcliffe@mathstodon.xyz avatar

@stpaultim Technically, that is a correct answer.

davidradcliffe, to random
@davidradcliffe@mathstodon.xyz avatar

I've always been afraid to end a sentence with a number and an exclamation point, because some smart-ass might intentionally misinterpret it as a factorial. But I will fear this no longer in this year of 2023!

davidradcliffe, to random
@davidradcliffe@mathstodon.xyz avatar

Help, I'm an old person. What does the symbol with the arrow followed by a vertical bar mean?

davidradcliffe, to random
@davidradcliffe@mathstodon.xyz avatar

This has me going until I remembered that the minimum number of clues for a proper Sudoku is 17.

davidradcliffe,
@davidradcliffe@mathstodon.xyz avatar

@SvenGeier There is no valid Sudoku with 16 clues. https://arxiv.org/abs/1201.0749

davidradcliffe, to random
@davidradcliffe@mathstodon.xyz avatar

It just occurred to me that the old Twitter logo is bouba and the new Twitter/X logo is kiki. https://en.wikipedia.org/wiki/Bouba/kiki_effect

davidradcliffe, to random
@davidradcliffe@mathstodon.xyz avatar

I don't understand why Musk wants a boring old 𝕏 when the Cool S is available.

ZachWeinersmith, to random
@ZachWeinersmith@mastodon.social avatar

http://smbc-comics.com/comic/niiiice

davidradcliffe,
@davidradcliffe@mathstodon.xyz avatar

@ZachWeinersmith

Here are four 'words' whose letters add up to 420:

  • breach of trust with fraudulent intent

  • center for disease control and prevention

  • cercopithecus aethiops pygerythrus

  • laser-assisted in situ keratomileusis

  • security intelligence review committee

davidradcliffe, to random
@davidradcliffe@mathstodon.xyz avatar

If a>1, then f(x) = a^x is the unique increasing function that satisfies f(1)=a and f(x+y)=f(x)*f(y) for all x,y. This could be taken as the definition of a^x. Has anyone developed real exponents in this manner? Any nice proofs of existence and uniqueness from first principles?

gregeganSF, to random
@gregeganSF@mathstodon.xyz avatar

[1/2] This sequence of squares has the property that their combined projections onto the x and y axes are always the full intervals [-1,1], while their projections onto any other lines (e.g. the red or green) tend to sets of measure zero, as does the set of squares itself.

A sequence of patterns of squares, starting with a single large square, where at each stage all squares are replaced by four squares, 1/4 the width, inside the original, staggered so their projections onto the x and y axes still encompass the same range of coordinates as the original square.

davidradcliffe,
@davidradcliffe@mathstodon.xyz avatar

@gregeganSF Very nice! So it's the Hough transform of a Cantor set.

pbump, to random
@pbump@journa.host avatar

So when gangsters go into the neighborhood and give out money to build goodwill, do the people think it's a sign the gangster is turning away from a life of crime? https://www.washingtonpost.com/politics/2023/07/11/ron-johnson-pga-liv-saudis/

davidradcliffe,
@davidradcliffe@mathstodon.xyz avatar

@pbump Johnson says that sports might help "modernize" Saudi Arabia. They are as modern as we are, if not more so. Modernity doesn't always lead to respect for human rights.

KeithDevlin, to random
@KeithDevlin@fediscience.org avatar

https://mathvalues.squarespace.com/masterblog/chatgpt-for-mathematicians-a-tool-in-search-of-good-applications

davidradcliffe,
@davidradcliffe@mathstodon.xyz avatar

@KeithDevlin ChatGPT is bad at reasoning, but it's great at transforming text. For example, it should be possible to take pictures of handwritten lecture notes with your phone and convert them to LaTeX documents automatically. I think that we will find lots of good applications once we stop trying to use the tools for things that they can't do.

  • All
  • Subscribed
  • Moderated
  • Favorites
  • •
  • megavids
  • thenastyranch
  • rosin
  • GTA5RPClips
  • osvaldo12
  • love
  • Youngstown
  • slotface
  • khanakhh
  • everett
  • kavyap
  • mdbf
  • DreamBathrooms
  • ngwrru68w68
  • provamag3
  • magazineikmin
  • InstantRegret
  • normalnudes
  • tacticalgear
  • cubers
  • ethstaker
  • modclub
  • cisconetworking
  • Durango
  • anitta
  • Leos
  • tester
  • JUstTest
  • All magazines
    •