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

All Cambridge University Press textbooks are freetoread until May ().

Nongray grayscales (). Rebecca Weber finds a method to produce offgray colors in a range of lightness with visuallymatching 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 (). This is one of my favorite papers in the list accepted to SoCG 2020, which now will be onlineonly. 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 (). Now a Good Article on Wikipedia.

The four points, two distances problem (). 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 HarPeled 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.

Two linocut interpretations of a rhombic dodecahedron by the same artist, Josh Millard: abstract and physical ().

Three recent “Did you know?” ():

… that Chiara Daraio used Newton’s cradle to create sound bullets, and ball bearing filled walls to create oneway 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 (). Many linked galleries of images of mathematical art, from the 1990sstyle web (occasional broken links and all).

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 ()? 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 glidercollision junk makes it more complicated.

Monotone subsets of uncountable plane sets (). I ask on MathOverflow about infinite generalizations of the Erdős–Szekeres theorem on the existence of squarerootsized monotone subsets of finite sets of points in the plane.