Linkage

Does anyone but me find it odd that car tire sizes are measured in millimeters for width, inches for inner radius, and a dimensionless number expressed as a percentage for (difference between inner and outer radius)/width (\(\mathbb{M}\))? Imagine the fun if we tried to do solid geometry this way.

American Astronomical Society switches to open source for all its journals (\(\mathbb{M}\), via). The fine print is a hefty >$1000paper publication charge with only a vague hope of waivers for some journals and not even that for one of them. Publication is not without cost, but comparing this with the actualcost €60/paper charges of LIPIcs suggests that there’s a lot of profit/overhead built into the AAS fees.

You may have heard that Fibonacci numbers form a meetsemilattice under divisibility, and that the map from \(n\) to \(F_n\) is a meetsemilattice homomorphism (\(\mathbb{M}\)). But did you know they’re actually a lattice, almost the same as the positive integer divisibility lattice (an infinitedimensional grid with a dimension per prime), but missing one element at the index \(2\) (because \(F_2=F_1=1\))? Unfortunately, because of the missing grid element, \(F\) is not a lattice homomorphism.

Point sets with no four collinear and no large visible island (\(\mathbb{M}\)). If you project a \(3\times 3\times \cdots\times 3\) grid linearly into the plane, for a generic projection, then there are no four points in a row. But if you choose the projection carefully, you can get another property: every convex subset of the plane that hits more than a constant number of points includes at least one threepoint line. New preprint by UCSD undergrad Sophie Leuchtner and Andrew Suk.

Possibly the earliest known example of folding (\(\mathbb{M}\)): an Egyptian map from over 3000 years ago. The link unfortunately lacks pictures but they can be found on the Wikipedia article on the same map, which however suggests an alternative hypothesis than folding for its markings.

Springer journal Scientometrics retracts a journal paper on predatory publishing after predatory publisher Frontiers objects to its use of a list of predatory publishers that lists Frontiers as a predatory publisher (\(\mathbb{M}\)). A followup comment connects the dots: “Notably, Springer owns a stake in Frontiers, although they rarely mention this publicly”. Editors of the Springer journal call the retraction misconduct and consider resigning from its board in protest.

Removing halftoning artifacts from images by FFT+masking (\(\mathbb{M}\), via). A nice illustration of how the right piece of mathematics can seem like “some sort of witchcraft that should not be possible”. The original uses a piece of software I haven’t used called Fiji, but there’s also the “Pattern Suppressor” Photoshop plugin for similar manipulations.

Ksenia Coffman’s work stomping out Naziglorification on Wikipedia (\(\mathbb{M}\), see also).

Quanta has a new article (\(\mathbb{M}\), see also) on the book The Disc Embedding Theorem by Behrens, Kalmar, Kim, Powell, and Ray, attempting to clarify Freedman’s early1980s 4manifold classification, which many found insufficiently rigorous. But it’s not the only book on this; there’s also Calegari’s The 4Dimensional Poincaré Conjecture, and Freedman’s Topology of 4manifolds (with Frank Quinn, 1990). Third time’s the charm?

Citation bias (\(\mathbb{M}\)): how the tendency to cite certain types of results over others (e.g. positive more than negative) and academic games of telephone can herd the research community towards a distorted view of what the scientific record has actually established.

The annual Graph Drawing symposium really loves hybrid formats (\(\mathbb{M}\)). This year’s symposium will be held this Wednesday through Friday as a hybrid of a small inperson meeting in Tübingen and online for those like me still not traveling. And, as in past years, the proceedings is a hybrid of a Springer LNCS volume (not yet out) and an arXiv copy, newly up at arXiv:2109.04863. If anything the arXiv version is better: more timely, with appendices and color both allowed.

Death of the Jekyll static site generator proclaimed (\(\mathbb{M}\), via), because of some open source politics I don’t understand. Meanwhile for those of us using it as a static site generator and githubpages blog springboard, Jekyll still largely just works as it always has without much need for development. Indeed, a big reason for the lack of momentum for going from Jekyll 3 to 4 is that it was an unnecessary incompatible update that would have broken too much stuff.

Why would someone plagiarize the bibliography of their journal paper (\(\mathbb{M}\)), by copying someone else’s bibliography on a totally unrelated topic, in an inconsistent format to the references in the main text of the paper (no doubt copied from somewhere else)? Thomas Clausen looks more deeply than necessary at the garbage pile that is predatory publishing, triggered by an odd citation alert.

\(\exists\mathbb{R}\), the problem of testing the existence of solutions to polynomial real equations is only a little harder than \(\mathsf{NP}\), but \(\exists\mathbb{Z}\) is undecidable (Matiyasevich). Today I learned from Marcus Schaefer’s GD talk that rightanglecrossing graph drawing is \(\exists\mathbb{R}\)complete but that requiring in addition that the vertices have integer coordinates makes it \(\exists\mathbb{Q}\)complete (\(\mathbb{M}\)). That means we don’t know whether it’s decidable!