Linkage

Still at home, hoping the coffee arrives tomorrow as scheduled.

• Science diagrams that look like shitposts (\(\mathbb{M}\), via).

• All Cambridge University Press textbooks are free-to-read until May (\(\mathbb{M}\)).

• Non-gray grayscales (\(\mathbb{M}\)). Rebecca Weber finds a method to produce off-gray colors in a range of lightness with visually-matching hues and saturations. It’s not just a matter of plotting a straight line in HSL colorspace. (Found while looking for more information on her book Computability Theory, but nowadays there isn’t much actual math on her website.)

• Convex hulls of random order types (\(\mathbb{M}\)). This is one of my favorite papers in the list accepted to SoCG 2020, which now will be online-only. Point sets whose order type is uniformly random are different from randomly drawn points, and harder to study. Xavier Goaoc and Emo Welzl observe that the projective transformations of a random order type are equally likely, and use this idea to prove that these point sets typically have very small convex hulls.

• Greedy coloring (\(\mathbb{M}\)). Now a Good Article on Wikipedia.

• The four points, two distances problem (\(\mathbb{M}\)). Can you find all of the ways of arranging four distinct points in the plane so that they form only two distances? The link is not a spoiler but it has a separate link to the solution. “Nearly everyone misses at least one” says Peter Winkler; can you guess the one I missed?

• Sariel Har-Peled makes some suggestions for online conferences: all papers above threshold should be accepted, rather than imposing artificial acceptance rates, and authors should provide versions of their talks in multiple lengths.

• Minimal-stick examples of the knots \(9_{35}\), \(9_{39}\), \(9_{43}\), \(9_{45}\), and \(9_{48}\) (\(\mathbb{M}\)).

• Two linocut interpretations of a rhombic dodecahedron by the same artist, Josh Millard: abstract and physical (\(\mathbb{M}\)).

• Three recent “Did you know?” (\(\mathbb{M}\)):

  • … that Chiara Daraio used Newton’s cradle to create sound bullets, and ball bearing filled walls to create one-way sound barriers?

  • … that a tetrahedron with integer edge lengths, face areas, and volume can be given integer coordinates?

  • … that former college basketball star Amy Langville is an expert in ranking systems, and has applied her ranking expertise to basketball bracketology?

• VisMath MathArt (\(\mathbb{M}\)). Many linked galleries of images of mathematical art, from the 1990s-style web (occasional broken links and all).

• Sadly, graph theorist Robin Thomas has died (\(\mathbb{M}\)).

• What happens when half a cellular automaton runs Conway’s Game of Life and the other half runs a rolling version of Rule 30 pushing chaos across the border (\(\mathbb{M}\))? I wish I could see a larger scale of time and space to get an idea of how far the effects penetrate. If the boundary emitted gliders at a constant rate they’d collide far away in a form of ballistic annihilation but the boundary junk and glider-collision junk makes it more complicated.

• Monotone subsets of uncountable plane sets (\(\mathbb{M}\)). I ask on MathOverflow about infinite generalizations of the Erdős–Szekeres theorem on the existence of square-root-sized monotone subsets of finite sets of points in the plane.