Linkage

This seems like a good time to throw in a word of appreciation for archive.org and their wayback machine for making it so easy to make permanent links to online resources that might otherwise go away, such as other people’s Google+ posts. Just search for the link on archive.org and, if it’s not archived already, it will give you a convenient link to immediately archive it. There’s one of those hiding in the links below, and more among the older links on my blog.

• Elsevier news roundup (\(\mathbb{M}\)): German, Hungarian, and Swedish academics have been cut off from Elsevier journals after subscription negotiations broke down. Negotiations with the University of California are ongoing after a missed deadline. Access to Germany was restored but without any long-term agreement. And the editorial board of Informetrics resigned to protest Elsevier’s open access policies.

• The Rado graph (\(\mathbb{M}\)). Choose a random graph with countably infinite vertices by flipping a coin to decide whether to include each edge. Or, construct a graph with binary numbers as vertices, with an edge \(x\)—\(y\) when \(x\lt y\) and the \(x\)th bit of \(y\) is one. Or, construct a graph on primes congruent to 1 mod 4, with an edge when one is a quadratic residue mod the other. They’re all the same graph, and it has many other amazing properties.

• A comparison of two parallel Canadian grant funding tracks (\(\mathbb{M}\)) shows that when reviewers are told to focus on the investigator rather than the proposed investigation, they are significantly more biased against women.

• Paul Erdős died in 1996, but his most recent paper is from 2015, nearly 20 years later! (\(\mathbb{M}\), see also). It’s about Egyptian fractions – representations of rationals as sums of distinct unit fractions – and is motivated by the conjecture that it’s always possible for all denominators to be semiprime. That’s still open, but they prove that every integer has a representation with all denominators products of three primes.

• You can’t pack uncountably many Möbius strips into 3d space (\(\mathbb{M}\)). Known since the early 1960s for polyhedral embeddings, this has been recently generalized to arbitrarily messy topological embeddings, and to higher dimensions, in two papers by Olga Frolkina and by Sergey Melikhov.

• YBC 7289 (\(\mathbb{M}\)). This Babylonian tablet from 1800 BC – 1600 BC shows the sides and diagonals of a square with a very accurate sexagesimal approximation to the square root of two, “the greatest known computational accuracy … in the ancient world”. Now a Good Article on Wikipedia.

• NASA names a building after Hidden Figures subject Katherine Johnson (\(\mathbb{M}\)).

• Christian Lawson-Perfect 3d-prints interconnecting Herschel enneahedra. This is the simplest non-Hamiltonian polyhedron. I wrote a couple years ago about Lawson-Perfect’s quest for a nice polyhedral realization for these shapes; now they exist in tangible form.

• Goldilogs and the \(n\) bears: a parable of algorithmic efficiency (\(\mathbb{M}\)).

• Karl Bringmann and Kasper Green Larsen have won the 2019 Presberger Award (\(\mathbb{M}\)), for outstanding contributions by young scientists in theoretical computer science, to be presented later this year at ICALP. The award laudatio appears not to be ready yet but committee chair Jukka Suomela writes that it is “for their groundbreaking work on lower bounds”.

• The Computational Geometry Week Optimization Challenge (\(\mathbb{M}\), via) is a contest to solve a hard problem in computational geometry, finding a simple polygon of minimum or maximum area with a given point set as its vertices. The 247 challenge instances are now online, with a deadline of May 31 for solving them.

• Problems with a Point: Exploring Math and Computer Science (\(\mathbb{M}\), via), a new book of mathematical essays from Bill Gasarch and Clyde Kruskal, based on expanded and cleaned-up versions of Bill’s blog posts at the Computational Complexity blog.