@mjd@mathstodon.xyz
@mjd@mathstodon.xyz avatar

mjd

@mjd@mathstodon.xyz

I am an amateur mathematician, but not the angle-trisecting kind.

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mjd, to random
@mjd@mathstodon.xyz avatar

I loved this:

  1. How many photons does Voyager send per bit transmitted?
  2. Many photons are received per bit received?
  3. How close are we to the theoretic lower limit of what we need to receive

https://physics.stackexchange.com/a/816710/9062

simontatham, to random
@simontatham@hachyderm.io avatar

It's annoying that shutdown(SHUT_WR) handles duplicate fds backwards.

I open a socket and fork(), so one process can read and the other write. If the writer wants to send EOF, it has to explicitly SHUT_WR. If it crashes without doing so, EOF is never sent.

With pipes, the reader closes its copy of the writing pipe, and EOF happens once the other copy closes – explicitly or not.

But no socket API call has the semantics of 'I don't want to write any more, but maybe someone else still does'.

mjd,
@mjd@mathstodon.xyz avatar

@simontatham The Berkeley folks screwed that up In The Beginning. Some would-be genius decided to make the API different than it was for pipes, probably because it seemed ⸢simpler⸣, and then didn't revisit that decision when they realized they now needed shutdown(2).

May a merciful God deliver me from ⸢clever⸣ programmers.

mjd, to random
@mjd@mathstodon.xyz avatar

I suspect that once I eat my vegetables I'll find that I like them after all.

But one confounding issue is that Haskell doesn't really have a (\emptyset) type, it only has a ({\bot}) type.

mjd, to random
@mjd@mathstodon.xyz avatar

I suppose g _ = undefined stands in adequately for a function of type Void -> Void but I'm not satisfied and I'm also not sure what I would say to someone who asked what else I could want.

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

An answer to a 100-year-old puzzle. I say an answer, because there is still part of the question that's open.

EDIT: The author/discoverer is here on Mathstodon!

https://mathstodon.xyz/@vesatimonen

And his post of this:

https://mathstodon.xyz/@vesatimonen/112513347111148808

mjd,
@mjd@mathstodon.xyz avatar

@ColinTheMathmo the discoverer, Timonen, seems to be a well-known designer of geometric puzzles https://pulmallinentapaus.blogspot.com/2014/04/an-interview-with-vesa-timonen.html

mjd, to random
@mjd@mathstodon.xyz avatar

This is the world's first use of the modern equals sign, from Robert Recorde's 1557 book The Whetstone of Witte.

(Screencap from Internet Archive's scan of the book: https://archive.org/details/TheWhetstoneOfWitte/page/n237/mode/2up)

(I also wrote a blog post a couple of years back explaining what it says if you are interested: https://blog.plover.com/math/recorde.html)

mjd, to random
@mjd@mathstodon.xyz avatar

If Cypher's plan in The Matrix to murder the others had been successful, would the Machines have kept their promise to reconnect him and make him wealthy and content? Or would they have thrown him away like garbage?

mjd, to random
@mjd@mathstodon.xyz avatar

Over the years the word for people who write computer programmers has changed from “programmers” to “coders” and now to “developers”. When did this happen, and why?

mjd,
@mjd@mathstodon.xyz avatar

@simontatham what word could replace 'treat' and be more concrete?

mjd, to random
@mjd@mathstodon.xyz avatar

TIL that although it's not primitive recursive to compute Ackemann's function (A(x, y)) for given (x) and (y), it is primitive recursive to check whether (A(x,y)= z) for given (x, y, z).

https://mathoverflow.net/a/19743/44852

mjd, to random
@mjd@mathstodon.xyz avatar

Take a look at this email and let me know what you think.

http://plover.com/~mjd/misc/Ask%20me%20anything.txt

I have gotten a lot of incoherent and bizarre email over the years, but never anything quite like this.

mjd, to random
@mjd@mathstodon.xyz avatar

For the first time, the complete connectome of an insect brain (drosophila larva) has been mapped.

https://www.science.org/doi/10.1126/science.add9330

It has 3016 neurons and 548,000 synapses. For comparison, c. elegans has 302 / 6702.

fanf, to random
@fanf@mendeddrum.org avatar

had a fun conversation in the pub this evening about practical chemistry

TIL conical flasks are safety equipment!

when a reaction gets too energetic, a conical flask will blow its bottom out and drop the mess on the bench or the floor

instead of exploding in all directions

ie not towards the experimenter’s face and eyes

clever design!

mjd,
@mjd@mathstodon.xyz avatar

@fanf I didn't know that, I thought it was just because they are hard to tip over

jonmsterling, to random
@jonmsterling@mathstodon.xyz avatar

Ultimately we have to ask ourselves if it was overall a good thing that computer science as a discipline ceased to be part of mathematics — rather than broadening the horizons of mathematics and bridging the gap between mathematics and social science. I am not speaking purely rhetorically, as there are legitimate arguments to be made on both sides.

mjd,
@mjd@mathstodon.xyz avatar

@boarders @antoinechambertloir @jonmsterling Just yesterday I was pondering his remark that “The establishment of a truly operational semantics of algorithms is perhaps the most important problem in computer science.”

I love Girard.

christianp, to random
@christianp@mathstodon.xyz avatar

Happy 175th birthday to Felix Klein, and happy 12th birthday to @aperiodical!
For our very first post, a youthful-looking @standupmaths and @stecks shared their top N facts about the Klein bottle: https://aperiodical.com/2012/04/top-n-facts-about-the-klein-bottle/

mjd,
@mjd@mathstodon.xyz avatar

@christianp @aperiodical @standupmaths @stecks Now I am curious to learn the bottom N facts about the Klein bottle.

mjd, to random
@mjd@mathstodon.xyz avatar

New logic post on my blog: “Well, I guess I believe everything now! ”

https://blog.plover.com/math/logic/k2.html

mjd, to random
@mjd@mathstodon.xyz avatar

But today's baffling Math SE question is similarly difficult: “A bag contains 5 balls of unknown colors. A ball is drawn and replaced twice. In each occasion it is found to be red. Again two balls are drawn at a time. The probability of both the balls red is?”

https://math.stackexchange.com/q/4903525/25554

mjd, to random
@mjd@mathstodon.xyz avatar

The hardest math problem I've ever seen on Math SE is this: Four marbles are drawn from a bag. What is the probability that two of them are white?

b0rk, to random
@b0rk@jvns.ca avatar

I've been criticizing git nonstop for months on here but I really do love it. I've been using it for probably 13 years, I'm used to all of the warts that I run into regularly, and I don't think I've had a major problem with it anytime in the last 7 years or so.

not to minimize all of the very real problems that people have with git but I really do believe that it's possible to use git successfully

mjd,
@mjd@mathstodon.xyz avatar

@b0rk I feel pretty much the same way, but all the same I'm eagerly hoping that whatever replaces it will be better.

fanf, to random
@fanf@mendeddrum.org avatar

surely this version of the joke should go,

concurrency is two of the hardest problems in computer science

https://buttondown.email/hillelwayne/archive/what-makes-concurrency-so-hard/

mjd,
@mjd@mathstodon.xyz avatar

@fanf

“Ask me what's the hardest thing about concurrent programming.”

“Okay, what's the hardest th—”

“TIMING!”

mjd, to random
@mjd@mathstodon.xyz avatar

What's a good way to draw a diagram of a not-necessarily transitive partial order? Hasse diagrams really want the order to be transitive.

((The orders I want to draw are: the nodes are permutations of ({1,2,\ldots n}) and (P\prec Q) whenver (\sum_{Q(i)<P(i)} i < \sum_{P(i)<Q(i)} i).))

mjd, to random
@mjd@mathstodon.xyz avatar

“Instead of exploding in rage, [Murderbot] decides it's going to half-ass its job and watch entertainment media instead.… Humans making that choice is probably one of the reasons we still exist as a species.”

( https://marthawells.dreamwidth.org/649804.html , via @katenepveu )

mjd, to random
@mjd@mathstodon.xyz avatar

Someone in Math SE wants to know how many ways there are to 3-color the vertices of an icosahedron and although I'm not sure what their difficulty is I feel sure that it is not mathematical.

mjd, to random
@mjd@mathstodon.xyz avatar

We don't consider 1 to be a prime number, but it wasn't always so. The convention has been different in different times and places.

“But then the statements of all your theorems would have to exempt 1,” you cry. Not so. Many would. Some would not.

On some other planet there is a culture of mathematicians who don't consider 2 a prime. When they meet us, they are surprised. “But then the statements of all your theorems will have to exempt 2,” they will cry. Our answer will be the same: many do. Some do not.

(Bonus trivia: the Treviso Arithmetic of 1478, perhapsthe earliest-known European arithmetic textbook, says unequivocally that the numbers begin with 2 and that 1 is not a number.)

mjd,
@mjd@mathstodon.xyz avatar

@christianp a friend once told me he heard his father, after half an hour of silence in the next room, loudly pronounce “ONE”.

He went into the next room to ask what was going on.

“I'm counting my belly button.”

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

Hindustani music has lots of ragas, but they're often organized into the 32 kinds shown here, of which only 10 are very commonly used. These kinds are called "thaats".

Each thaat is a 7-note scale. I'll explain them in a western way, not an Indian way. This will make it clear how 𝑢𝑛𝑠𝑢𝑟𝑝𝑟𝑖𝑠𝑖𝑛𝑔 the ideas are to anyone who has studied western music theory.

Let's imagine our thaat starts with the note C. Then:

• it must contain C
• it must contain D or D♭, but not both
• it must contain E or E♭, but not both
• it must contain F or F♯, but not both
• it must contain G
• it must contain A or A♭, but not both
• it must contain B or B♭, but not both.

So, we get 2⁵ = 32 thaats. It's really unsurprising that C and G are locked in place, while the other 5 notes are flexible - after all, C and G are the 'tonic' and 'dominant', also called the 1 and 5, the most important notes in a scale.

A lot of thaats match familiar western modes, but later I'll show you some that may not. Maybe some expert on jazz can say if they've seen them.

Thaats are just the start of the story, since we can get extra ragas by leaving out some notes in a thaat... and as a result, different ragas can come from the same thaat.

But there's a more urgent issue: what are all the letters in this chart? The notes in the thaat are called

sa re ga ma pa dha ni

or for short

S R G M P D N

These are a lot like the western "do re mi fa so la ti".

But as I've said, we get a binary choice only for 5 of these notes, namely R G M D N, since the other 2 are locked in place. That's what the chart shows. It's a binary tree with 32 leaves, namely the thaats.

(1/n)

mjd,
@mjd@mathstodon.xyz avatar

@johncarlosbaez It's interesting that it starts at M in the middle and follows the circle of fifths downwards. A Western version would most likely have gone in the reverse order.

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