Linkage

3d-printed models of the chaotic attractors from dynamical systems (\(\mathbb{M}\)). Stephen K. Lucas, Evelyn Sander, and Laura Taalman in the cover article of the latest Notices.

Complete classification of tetrahedra whose angles are all rational multiples of \(\pi\) (\(\mathbb{M}\), via). The original paper is “Space vectors forming rational angles”, by Kiran S. Kedlaya, Alexander Kolpakov, Bjorn Poonen, and Michael Rubinstein.

Geometry strikes again (\(\mathbb{M}\), via), Branko Grünbaum, Math. Mag. 1985. Somehow I don’t think I’d encountered this short paper before but it’s filled with many examples of horribly-drawn mathematics, one in the logo of the MAA. Worth reading as a warning for what not to do. Also for clear instructions on how to draw regular icosahedra correctly.

Ethical issues in large-corpus natural language processing, or what’s behind the research that got Timnit Gebru kicked out of Google (\(\mathbb{M}\), via).

How one university (Brown) tracks the physical locations of its students to ensure compliance with its pandemic safety policies (\(\mathbb{M}\), via). Most of it is pretty obvious: if you use a campus keycard or connect to a campus wireless network, they know you’re on campus.

How prestige journals remain elite, exclusive and exclusionary (\(\mathbb{M}\), via). Nature is charging up to €9,500 per paper in open-access fees, as much as some scientists in third-world countries earn in a year, making open-access publication inaccessible to people from low- and middle-income countries.

Euclidean distance (\(\mathbb{M}\)), now a Good Article on Wikipedia.

Ingo Ullisch and the goats (\(\mathbb{M}\)). A new solution to the problem of how to bisect the area of a circle by another circular arc centered on the first circle. But, given that it involves integrals and trig, is it really fair to call it “more exact” than the previous solution? I don’t think we even know whether the solution radius is transcendental (or transcendental over \(\pi\)).

Anila Quayyum Agha’s openwork sculptures cast intricate tessellated shadows on the surrounding surfaces (\(\mathbb{M}\)). See also her Wikipedia article and two stories on her work, “Between light and shadow at the Toledo Museum of Art” and “Anila Quayyum Agha on drawing inspiration from darkness”.

Pat Morin notes that it’s “good to see that the pandemic hasn’t affected every aspect of our lives”: the registration fees for the online SODA conference are still way too high.

IEEE has no mechanism to publish corrections or errata to conference proceedings papers (\(\mathbb{M}\), via), violating IEEE’s own code of ethics requiring authors “to acknowledge and correct errors”: Probably many other conference proceedings have similar issues.

Shallow trees with heavy leaves (\(\mathbb{M}\)). On “the general strategy of searching much fewer positions and expending more effort on each position”, and its application in using SAT solvers to find new spaceships in cellular automata.

Dictionary of mathematical eponymy: The Xuong tree (\(\mathbb{M}\), see also), a special kind of spanning tree in graphs, used to embed them into surfaces with as high a genus as possible.

An explicit PL-embedding of the square flat torus into \(\mathbb{E}^3\) (\(\mathbb{M}\)). The square torus is like the old Asteroids arcade game: a Euclidean square with boundary conditions that wrap around so if you move off one edge you re-enter at the corresponding point of the opposite edge. In 4d, it has a nice representation as the set \(\{(a,b,c,d)\mid a^2+b^2=c^2+d^2=1\}\), the Cartesian product of two circles. The Nash embedding theorem gives it fractal embeddings in 3d, but Tanessi Quintanar finds it as a bona fide polyhedron.