Challenge for applied category theory: build a ronavirus, so that the world can be sane again.

#DataVisualization can help us make sense of and teach about the coronavirus, but the stakes are high. @abmakulec@twitter.com has 10 considerations to help you #VizResponsibly:

medium.com/nightingale/ten-con

Who called it a magma and not a hemidemisemigroup?

ah yes, the classic proof

Mathemagics
Article by Pierre Cartier
In collections: Notation and conventions, The act of doing maths
My thesis is:there is another way of doing mathematics, equally successful, and the two methods should supplement each other and not fight.
URL: ftp.gwdg.de/pub/misc/EMIS/jour

I've just noticed that if you choose "wheelchair accessible" on google maps directions, it still shows an icon of a dude walking

The innovation here seems to be in the emphasis placed on the properties of the sum of the roots and the product of the roots.

And now, substituting into the formula for $$r$$ and $$s$$, we get $$r, s = -\frac{b}{2} \pm \sqrt{\frac{b^2}{4} - c}$$.

But this is just the same as $$\frac{-b \pm \sqrt{b^2 - 4c}}{2}$$, which is exactly what we would expect from the standard formula, given that $$a=1$$! The general derivation, for $$a \neq 1$$, takes a few more steps, but is fairly straightforward.

Now, the only way we can have $$r+s = -b$$ is if $$r = -\frac{b}{2} + z$$ and $$s = -\frac{b}{2} - z$$, for some $$z$$.

Since $$rs = c$$, this means that $$c = \frac{b^2}{4} - z^2$$.

Rearranging, we get $$z = \pm \sqrt{\frac{b^2}{4} - c}$$.

The trick is as follows: Assume, first of all, that $$a=1$$, and let $$r$$ and $$s$$ be the (unknown) roots. Then we can write $$x^2 + bx + c = (x - r)(x - s)$$.

Expanding the right-hand side, we get $$x^2 + bx + c = x^2 - (r+s)x + rs$$.

So we have $$r + s = -b$$, and $$rs = c$$.

Maths educator Po-Shen Loh has discovered a way to solve quadratic equations that is much more intuitive than $$\frac{-b \pm \sqrt{b^2 - 4ac}}{2a}$$, and is apparently unprecedented in the entire 4000-year history of thought on quadratic equations! See arxiv.org/abs/1910.06709.

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

A few days ago, my coworker @sjockers@twitter.com told me that you can MOVE the screenshot selection – Command+Shift+4 – when you keep SPACE pressed on a Mac. I'm still blown away by that.

lots of people discussing cultural norms without defining their cultural vector space

Earliest Uses of Various Mathematical Symbols
Web page by Jeff Miller
In collections: History, Notation and conventions
These pages show the names of the individuals who first used various common mathematical symbols, and the dates the symbols first appeared. The most important written source is the definitive A History of Mathematical Notations by...
URL: jeff560.tripod.com/mathsym.htm

What are your favorite tiny tools when working with data?

Here are three examples:
ucbvislab.github.io/d3-deconst to get the data out of d3 visualizations
shancarter.github.io/mr-data-c convert CSV to JSON
countries.zeto.io input country name, output country codes (by @zeto@twitter.com)

This is fun! typing game! My PB so far is 36, what's yours?

texnique.xyz/

Yesterday, I played a game of Dialect with @skalyan and two other people in the Guild in Canberra. We narrated the story and language of the bots in charge of maintaining and preserving Waste-/Land, a nature reserve/hazard waste dump planet long forgotten by humanity. The game worked really well (I think it deserves its ENnie nomination), apart from the fact that we were not good at streamlined Conversation framing and resolution, but that can be improved by re-reading the rules.

Leiden wall formulas: muurformules.nl/

The last time I was in Leiden they were decorating the exterior walls of all their buildings with poems of many different languages. Now they've moved on to the language of mathematics.

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