@christianp@mathstodon.xyz
@christianp@mathstodon.xyz avatar

christianp

@christianp@mathstodon.xyz

Mathematician, koala fan, mathstodon.xyz admin,
⅓ of https://aperiodical.com. He/him

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

christianp, (edited ) to random
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What do you think is the furthest you've ever been from any living people?
Order of magnitude will do: 100m, 1km, 10km, 100km?

I think solo pilots or sailors will boss this, but I'm also interested in the answer for plebs like me who rarely travel solo.

christianp, to random
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Somebody who's good at linear algebra, tell me: what are eigenvectors good for?

christianp, to random
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I appreciate it's frustrating that the site is slow, but telling me it's still slow won't make me fix it any quicker and won't help my stress level

christianp, to random
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Loads of new people on mathstodon lately. Is this all @samjshah's doing, or is something else going on?

christianp, to random
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Who can find a street with a number in its name that's bigger than the number of any building on that street?

christianp, to random
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Wild how the same university that wanted to reduce my paid hours by 20 minutes each day to account for lunch breaks also wants me to come in on Saturdays to help with open days.

christianp, to science
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You have pieces labelled 1 to N.
You arrange them in a line N times, so that at turn k the piece labelled k is in position k. (so on the first turn piece 1 is at the start, on turn 2 piece 2 is next to that, and so on)
No piece can be in the same position for two consecutive turns.

How many ways of doing this are there?

For N=3, there's only one:
On turn 1, it must be 1xx
On turn 2, it must be x2x and 2 can't be where it was before, so turn 1 was 132 and turn 2 is 321.
On turn 3 it must be 213.

For N=2, it can't be done.

For N=4, there are loads of ways.

christianp, (edited ) to random
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The following will probably only make sense to people in the UK.

I have a vague sense that the job of "lollipop person" used to be fairly strongly gendered, but I can't remember which way - is it lollipop man, or lollipop lady? I feel like "lollipop lady" sounds more like what I said growing up, but both lollipop people at my kids' school are men and I've overthought it and now I'm suffering from semantic satiation.

So, was it a lollipop man or a lollipop lady when you were at school?

christianp, to typst
@christianp@mathstodon.xyz avatar

This morning I'm looking at .
The first thing in the tutorial (https://typst.app/docs/tutorial/writing-in-typst/) is how to write a header, and it annoys me that it makes the same mistake HTML, and everything following HTML, made: you specify the level of the heading absolutely, and it's not scoped to a section of the document.

So when you want to have a heading one level lower, you have to know what level the previous heading was. And you can't tell how much of the document the heading applies to, only inferring it as going until the next header of the same or higher level.

I've always wondered why has
\section{name}
instead of
\begin{section}{name} ... \end{section}

Am I alone in wanting this?

christianp, to random
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Here's a sequence of integers that isn't in the OEIS. I think it has to be a triangle read by rows:

1
2,1
2,3,1
4,2,3,1
4,2,3,1,5
6,4,2,3,1,5
6,4,2,3,1,7,5
6,4,8,2,3,1,7,5
6,4,8,2,9,3,1,7,5

Can you work out the rule for making the next row from the last?
Are there any patterns that you can spot?

As ever, I can give hints at different levels on demand. Please put any potential solutions under a content warning.

christianp, to random
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I've got the morning to myself, so I'm working on upgrading mathstodon.xyz to Mastodon 4.2.0. Hopefully it'll all be done before lunchtime.

christianp, to random
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They all laughed when I wrote code to simulate long division by hand!

Well, today I had a serious reason to use it.

Who's laughing now?!

(not me, I'm crying about the edge cases)

christianp, to random
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Having to bite my fist: mustn't upset people who don't know better.

My colleague in the central EDI team publishes a newsletter. He's not at all technically minded, so he uses Microsoft Sway, since it's there and it seems to look nice.

It reloads the page when you resize the window! It forces you to reload the page if it's been open for "too long"!
WHAT

The newsletter contains some audio files (which he thinks are podcasts) and videos, which can't be opened in a new tab or linked to. They can't even be downloaded: I tried to get their URL from the inspector, and they're only fetched as fragments by repeated requests, instead of just downloading the file.

ARGRGRRRGRGRGR

christianp, to random
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Would it be feasible to automatically gather all mathematical terms defined on wikipedia?
I looked at wikidata, but it doesn't look like there's a property to say that an item is a definition of a term, so I think the best I could do would be to wade through things in the Wikiproject Mathematics.

If I was looking at the text of articles, I suppose looking for the phrase "is called" in the page description would get most definitions.

christianp, to random
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Can anyone help with this error I've been getting since upgrading mathstodon.xyz to 4.2?
In Firefox, I get an error "downloadable font: rejected by sanitizer" when downloading https://mathstodon.xyz/packs/media/fonts/Sans/cmunss-0745961ddcecad8aa4fd00b9e39cce11.woff.
The Network tab says only 948B were transferred; the file is 77KB on disk. Because it's a font, Firefox won't show me the received raw data in the Response tab.
When I redo the request as a curl command, I get the whole file. I didn't change the nginx config when upgrading, and other woff fonts have loaded.
The font loads OK in Chrome.
I'm at a loss!

christianp, (edited ) to random
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Pals, what's the least egregious TV I can buy today, in the UK?
I want as little "smart" internet-connected nonsense as possible. Not bothered about 4k or massive size, but it should sound and look good.

That is, what's the Brother laser printer of TVs?

christianp, to random
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Huge sunk cost fallacy as I've spent all day hand-drawing every mathematical symbol in unicode, and even though my handwriting isn't very good I pretty much have to finish this t-shirt

christianp, to random
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On the ferry to the Netherlands 🇳🇱!

christianp, to random
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Meta, the company that owns Facebook and Instagram, is reportedly going to launch a new ActivityPub-compatible social network on the domain threads.net.

I and @ColinTheMathmo, the admins of mathstodon.xyz, are wary of the effect this will have on the fediverse, so we're pre-emptively blocking that domain until we see whether Meta plan on trying to federate, and if so, under what terms they do so.
Once it becomes clear how threads.net works, we'll decide whether to permanently block it.

christianp, to random
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Is this thing rotationally symmetric?
Poll in the next toot.

I have a photo looking down at it from above that I will post later.

christianp, to random
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Here's a game inspired by @two_star's "reverse the list of integers" game.

Get from one integer to another by a sequence of moves. Valid moves are:

  • EXPAND: replace a number with an equivalent mathematical expression, e.g. 5 → 1+4
  • EVALUATE: replace an expression with its numerical value, e.g. 1+4 → 5.
  • SWAP: swap a mathematical operation for another one, e.g. 1+4 → 1×4.

I'll put an example game in the next toot

christianp, to random
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On Sunday I published a video and a blog post on the @aperiodical about a really nice puzzle/solitaire game invented by Ed Kirkby, which I call "Double Back".
Have a look: https://aperiodical.com/2023/12/the-double-back-puzzle-is-a-nice-mix-of-towers-of-hanoi-and-solitaire/

christianp, to random
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Having an exciting time discovering that the web version of Microsoft Word seems to not bother rendering parentheses around factors that need them.

Like, it's showing me (81 - \rho^2) but it should be (8(1 - \rho^2)).

There's no way the author just forgot to put those parentheses in, right?

christianp, to random
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Pals, convince me not to buy this t-shirt: https://www.threadless.com/shop/

christianp, (edited ) to random
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You are shown a set of four cards placed on a table, each of which has a number on one side and a color on the other.

The visible faces of the cards show yellow, 5, 4, purple.

Which card(s) must you turn over in order to test that if a card shows an even number on one face, then its opposite face is purple?

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