Sierpinsky triangles in stone, on medieval floors in Rome: http://www.formulas.it/formulog/wp-content/uploads/2014/12/sierpinski-aplimat.pdf, Elisa Conversano and Laura Tedeschini Lalli. See also Kim Williams, "The pavements of the Cosmati", https://doi.org/10.1007%2Fbf03024339

The collection of images of these on Wikimedia commons, https://commons.wikimedia.org/wiki/Category:Sierpi%C5%84ski_triangles_in_Cosmatesque_pavements, is a little sad — Conversano and Tedeschini Lalli, and Williams, have a lot more.

_The Topkapı Scroll – Geometry and Ornament in Islamic Architecture_, by Harvard professor Gülru Necipoğlu, https://www.getty.edu/publications/virtuallibrary/pdf/9780892363353.pdf

One of many beautiful art books free for download from the Getty Virtual Library, https://www.getty.edu/publications/virtuallibrary/

Giant origami animals in Midtown Manhattan: https://www.thisiscolossal.com/2021/09/hacer-origami-sculptures/

But now I want to know if they were really each fabricated from a single uncut square sheet of steel. And if so, how did they get the corners so crisp?

I recently saw a link to Chapter 1 of the MathML 3.0 spec, https://www.w3.org/TR/MathML3/chapter1.html, using as an example the quadratic formula in both layout markup and content markup. Its totally unwieldy non-human-readable expansion obscures the fact that the MathML authors didn't even get the math right: their content markup silently replaces "±", by which the correct formula represents both solutions, with "+", giving only one of the two.

Time to re-link my old anti-MathML rant https://11011110.github.io/blog/2015/08/04/mathml-considered-harmful.html ?

New blog post: Multilayered tiles, https://11011110.github.io/blog/2021/09/25/multilayer-tiles.html

The integer-coordinate octagon shown below is an example: it cannot tile the plane (no convex octagon can), but placing copies of it at each integer point produces a 7-ply uniform covering of the plane.

Vi Hart's latest video mixes up discussions of the nature of social media, the philosophy of mathematical creativity, an exploration of symmetry, and an investigation of the spot patterns of 8-sided dice (which turn out not to all be the same) and how to visualize them.

I thought for sure I had posted before about Dinara Kasko's 3d-printed geometric food designs, but grep tells me that if I ever did, it wasn't with her name.

Bold New Mathematical Cake Designs by Dinara Kasko:

https://www.thisiscolossal.com/2017/09/bold-new-geometric-cake-designs-by-dinara-kasko/

La repostería matemática de la arquitecta Dinara Kasko: https://culturainquieta.com/es/arte/diseno/item/12643-la-reposteria-matematica-de-la-arquitecta-dinara-kasko.html

Kasko's own web site:

https://dinarakasko.com/

Three sets of talk slides from recent talks (unfortunately I don't have links to recordings of the talks):

The graphs of stably matchable pairs, WG 2021: https://www.ics.uci.edu/~eppstein/pubs/Epp-WG-21-slides.pdf

A stronger lower bound on parametric minimum spanning trees, WADS 2021: https://www.ics.uci.edu/~eppstein/pubs/Epp-WADS-21-slides.pdf

Limitations on realistic hyperbolic graph drawing, GD 2021:

https://www.ics.uci.edu/~eppstein/pubs/Epp-GD-21-slides.pdf

Inside Higher Ed on the future of academic conferences: https://www.insidehighered.com/news/2021/09/13/future-academic-conference

A significant fraction of academics surveyed said that they still felt unsafe going to physical conferences, and with the carbon footprint and reduced expenses of virtual but greater interactivity of physical meetings, some mix of both seems likely going forward. However, trying to mix both in one conference (especially for conferences with many parallel small talks or panels) seems difficult and expensive.

Textbook company Pearson sues Chegg for copyright infringement, for selling solutions to textbook homework problems: https://www.insidehighered.com/news/2021/09/15/pearson-sues-former-partner-chegg-copyright-infringement

On the one hand, for-profit cheater-enablers like Chegg are a cancer on higher education. On the other, the solution to a problem is generally a concept, not a text, and should not be something that can be locked up under copyright.

So I don't know who to root for?

The annual Graph Drawing symposium really loves hybrid formats. This year's (https://algo.inf.uni-tuebingen.de/gd2021/) will be held this Wednesday through Friday as a hybrid of a small in-person 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 https://arxiv.org/abs/2109.04863

If anything the arXiv version is better: more timely, with appendices and color both allowed.

- Home page
- https://www.ics.uci.edu/~eppstein/

I'm a computer scientist at the University of California, Irvine, interested in algorithms, data structures, discrete geometry, and graph theory.

Joined Apr 2017