Linkage

As usual, follow me on Mathstodon to see these as I post them rather than two weeks later.

• Half of the 200 people who needed visas to attend one of the satellite workshops of NeurIPS 2018 in Montreal were unable to get them in time (\(\mathbb{M}\), see also), making it more likely that future conferences depending on international attendance will avoid Canada.

• This is not a cinnamon bun (\(\mathbb{M}\)). It’s actually a 160 million year old fossil snail shell from Madagascar, roughly the size of a large fist (or cinnamon bun). I don’t think it’s particularly rare or valuable; I picked it up because I liked its shape.

  

• Web site for generating knight’s tours of oversized chessboards with approximately-minimum numbers of bends and crossings (\(\mathbb{M}\)). For background on how it works, see the short paper by Besa, Johnson, Mamano, and Osegueda (all UCI students) in Graph Drawing 2018 pp. 661–663 – unfortunately I don’t know of a non-paywalled link.

• Besse Beulah Day (\(\mathbb{M}\)), in the 1940s, was one of the first to apply the design of experiments to engineering, after previously having learned to use the technique in forestry. Jacqueline Telford wrote about her briefly in a 2007 survey. Searching for the phrase “Besse Day, working at” finds that Telford’s account of Day’s work has been plagiarized by at least six other works. It’s a form of fame, I guess, to be copied so much.

• The slow rise and rapid fall of Göttingen as the world capital of mathematics (\(\mathbb{M}\)).

• An interview with Brazilian mathematician Carolina Araujo (\(\mathbb{M}\)) on the gender gap in mathematics and what still needs to be done to close it.

• If you sample enough times from an unknown distribution over an unknown finite subset of \([0,1]\), can you (with high probability) produce a finite set of measure at least \(2/3\)? (\(\mathbb{M}\), via, via2). Your set does not need to consist only of the points you’ve sampled! You can do it if \(2^{\aleph_0}=\aleph_k\) for finite \(k\) but not otherwise.

• Vijay Vazirani on the flocking behavior of theoretical computer scientists (\(\mathbb{M}\)). Vijay’s post also includes an announcement for a semester-long program on online and matching-based market design at the Simons Institute in Berkeley.

• The view from my desk (\(\mathbb{M}\)). Actually my office has lots of windows with a nice view of a well-used plaza, outdoor coffee shop, trees, and distant mountains. But to see that, I have to get up and go over to one of the windows. If I stay at my desk and look up at the window, I see this interesting geometric pattern instead.

  

• Gerard Westendorp made a snowdecahedron but global warming melted it.

• Online sliding block puzzles (\(\mathbb{M}\)) by Jacob Siehler. The goal is to swap the positions of two colored blocks. Even the easy ones are non-obvious.

• Cute proof of Sperner’s theorem (\(\mathbb{M}\)) from a talk by R. P. Stanley: represent subsets of \([0,n-1]\) by strings of
  \(n\) parentheses, “)” in position \(i\) if \(i\) is in the set, “(” otherwise. In each string, flip the first unmatched “(”, grouping the subsets into chains like (()(( – )()(( – )())( – )())). Each chain touches the middle level once, and any other antichain at most once, so the middle level is the biggest antichain.

• Two triangles in a convex point set can cross or overlap in eight configurations, colorfully named the taco, mariposa, bat, nested, crossing, ears, swords, and david by “More Turán-Type Theorems for Triangles in Convex Point Sets”, a new paper in Elect. J. Comb. by Aronov, Dujmović, Morin, Ooms, and Schultz (\(\mathbb{M}\)). For 246 of the 256 subsets of configurations, they find near-max families of triangles avoiding the subset. The remaining 8 subsets are equivalent to “tripod packing”, which is less well-understood but the subject of another newly published paper, “New Results on Tripod Packings” (Discrete Comput. Geom., by Östergård and Pöllänen). The tripod problem has a complicated history of independent rediscovery, not all of which was known to Östergård and Pöllänen, so see the EJC paper for a more thorough survey.

• Creating a 3D-printable Lorenz attractor (\(\mathbb{M}\)). From Elizabeth Denne’s “Visions in Math” blog which, sadly, seems to have gone on hiatus after publishing this in 2017.