Pinned toot

Hallo, new Mastodon users! Here on mathstodon.xyz we've got a couple of mathematical emoji: and . I'd love to add some more. If you can make a PNG image the same size as those, send it to me and I'll add it. Faces of famous mathematicians are an easy place to start; could we have some shapes, polyhedra, or other mathographics too?

I've spent two hours designing a Koch snowflake ornament to , and it looks like the printer is knacked. So that's a wasted morning!

I've just released a simple #ActivityPub debugging tool. It's hosted on Glitch so you don't have to worry about spinning up servers or SSL certs etc. You clone your own copy of the project, set it up, and you can create ActivityPub accounts that can send any raw JSON payload you specify to its followers. I use it for testing new and novel ActivityPub objects, and to test compatibility with messages sent from remote servers without needing to create an account on them.

tinysubversions.com/notes/acti

I've just discovered something incredible: Jim Fowler has compiled TikZ to WebAssembly! That means you can render TikZ diagrams in web pages, **on the fly**!!
I've made a demo page with an editor, so you can see it and believe it: tikzjax-demo.glitch.me

Today: trying to think of use cases for the new 'explore' mode in Numbas. It enables questions where the student can choose what to do next, and subsequent parts depend on answers to previous parts.
At the moment, I've got:

* choose which hypothesis test to do on this data
* how many roots does this equation have -> enter those roots
* ask for subsequent terms of a sequence, until you can write down the formula

Concatenation of numbers preserves divisibility, that is if $$a_1,\dots,a_n$$ are all divisible by d, then their concatenation $$a_1a_2\dots a_n$$ is also divisible by d.

Also while I'm picking on Wiley, how did the following paper ever pass peer review for their journal _Concurrency and Computation, Practice and Experience_ (or even a basic sanity check that it has a coherent topic that fits the mission of the journal? doi.org/10.1002/cpe.5484

Puzzle problem: Suppose $$A_1, A_2, \ldots, A_n$$ are finite sets, and each $$A_i$$ contains an odd number of elements. Prove that there is a set $$S\subseteq \left\{1, 2, \ldots, n\right\}$$ such that $$\displaystyle\sum_{i\in S} \left|A_i \cap A_j\right|$$ is odd for every $$j\in \left\{1, 2, \ldots, n\right\}$$.

A puzzle from the MSRI newsletter, Emissary:
"Each of the twelve faces of a dodecahedron has a light that is also an on/off button. Pushing the light causes all five of the lights on the adjacent faces to switch state (go from on to off, or the reverse). Prove that any of the 2¹² positions can be obtained from any other by a suitable sequence of button pushes."

If I'm honest, I'm sharing this because I solved it. I wasn't so clever with the other puzzles.

msri.org/system/cms/files/973/

The surprising link between recreational math and undecidability (blogs.scientificamerican.com/r): Evelyn Lamb describes how a seemingly isolated fact about Fibonacci numbers ($$F_n^2\vert F_m \Rightarrow F_n\vert m$$) led to Matiyasevich's solution to Hilbert's 10th problem, that there is no general algorithm for solving Diophantine equations.

non mathematicians: i hate math because i hate numbers

me, a mathematician: what the frick is a number

I've just given a talk at titled "Baked Sudoku"
Slides at somethingorotherwhatever.com/b, and an interactive version at glass-sudoku.glitch.me/

3D Hilbert curve stained glass triptych done!

‪Braiding gears. Three gears are linked in a chain, but you can “braid” them, rearranging how they connect to each other. Full video at youtu.be/Lh7yAbw0H24

is the study of what's true.
is the study of what can be true.
A Mastodon instance for maths people. The kind of people who make $$\pi z^2 \times a$$ jokes. Use $$ and $$ for inline LaTeX, and $ and $ for display mode.