Flip graphs of matroids are expanders: gilkalai.wordpress.com/2018/12
Gil Kalai reports on a new proof by Nima Anari, Kuikui Liu, Shayan Oveis Gharan, and Cynthia Vinzant of a conjecture by Milena Mihail and Umesh Vazirani that any subset \( S \) of at most half of the bases of a matroid has at least \( |S| \) flips to a base outside \( S \).

Based on a preprint at arxiv.org/abs/1811.01816, via plus.google.com/11727145723611

paperplanes Show more

LaTeX, quick poll Show more

Taylor and Francis doing Trump’s dirty work for him: gowers.wordpress.com/2018/12/0

Timothy Gowers reports on the journal _Dynamical Systems_ refusing to publish a paper (supposedly, arxiv.org/abs/1408.1835) after editorial acceptance because one of its coauthors is Iranian.

@bremner Oh good. I heard from someone else that the LA Times was making itself unavailable in Europe but I wouldn't think that should affect Canada.

New blog post: General-position hypercube projections

In which I look for large general-position subsets of 2d grids (the no-three-in-line problem) by starting with higher-dimensional point sets and then carefully flattening them. So far the results are only computational but they look promising.

@bremner Grr Balkanization of the web. The UC status page is still visible, at least, I hope.

@mike Sure, if you're technically inclined, you can use open source systems and secure your own hardware and feel reasonably secure. But it's important to have freedom from government snooping for the masses, not just for a small number of knowledgeable people. Not least because when there are only a small number of people for whom the regular snooping measures are insufficient, the snoopers can concentrate their power on those people.

Australia's war on encryption: the sweeping new powers rushed into law

With all the vague "end of the internet!" or "why is everyone so upset at such good idea" stories elsewhere on the new Australian backdoor-your-apps law, it's good to see a piece that explains what it actually does.

The moral seems to be: don't allow or agree to any automatic updates while in Australia. Australians, if you want security from govt snooping and from security flaws, tough luck.

ACM announces their 2018 class of fellows: acm.org/media-center/2018/dece
Congratulations, new fellows!

You can also see Wikipedia's coverage of all the ACM fellows at en.wikipedia.org/wiki/List_of_
Quite a few are still missing articles, so if you want to improve Wikipedia's coverage of computer scientists there's still plenty to do.

Rigid Foldability is NP-Hard: arxiv.org/abs/1812.01160

It was previously known that folding a purported origami folding pattern to a flat state is NP-hard, because you can encode logic in the way the paper gets in the way of itself. But this paper proves that it's hard even to tell whether you can make any rigid motion at all starting from completely unfolded paper, well before self-interference kicks in. Instead, the difficulty involves getting sums of angles to come out right.

How to make a hollow geodesic plywood ball

I don't actually care about the how-to part of the linked video, but the malachite-like patterns that emerge from the plywood layers on the resulting ball are quite pretty. If you think about it, it's reversed from actual malachite, where the 3d structure involves nested spheres, and you get the patterns from a flat cut. Here, the 3d structure involves flat layers, and you get the patterns from a spherical cut.

@christianp @mjd My first diagram is blue/pink (alternating around the outside) and green (in the middle). The second (the one you say is blue/yellow/black) is actually blue/yellow/red. Maybe I should switch to those colors throughout?

New blog post: Triply-Hamiltonian edge colorings

In mathstodon.xyz/@mjd/1010988538, Mark Jason Dominus (@mjd) observed that the regular dodecahedron can have its edges properly colored with three colors so that every two colors form a Hamiltonian cycle. In this post, I survey constructions for more graphs like this, and prove that no planar bipartite graph can have a coloring like this.

The State Court of Berlin has ordered the German-language Wikipedia to remove claims linking CS prof Alex Waibel to US intelligence. "Whether the claims were justified or not was not taken into account by the court" — instead it seems the court disagrees with Wikipedia's policy of repeating claims from published sources, and insists that potentially-harmful claims can only be published by people who have researched them directly.

heise.de/newsticker/meldung/Ur (in German), via en.wikipedia.org/wiki/Wikipedi

Larry Lessig on how "industry influence can affect even the ethically engaged professional" and how this corruption can lead to anti-scientific popular backlashes such as the anti-GMO movement: chronicle.com/article/How-Acad

Show more

A Mastodon instance for maths people. The kind of people who make \(\pi z^2 \times a\) jokes.

Use \( and \) for inline LaTeX, and \[ and \] for display mode.