• ## Grid majors

I’ve written here about grid minors before, more than once. These are grid graphs that you can get from a given graph $G$ as a minor (that is, by removing edges or vertices from $G$ and contracting others of its edges). So, in the other direction, a “grid major” of $G$ must be a grid graph that has $G$ as a minor. These are the subject of my new preprint, “Homotopy height, grid-major height and graph-drawing height” (arXiv:1908.05706, with Therese Biedl, Erin Chambers, Arnaud De Mesmay, and Tim Ophelders, to appear at Graph Drawing).

• ## Congratulations, Dr. Besa!

Juan Besa’s successful dissertation defense was last Thursday, but I’ve been holding off posting about it here because one of his committee members took ill and couldn’t sign off on it until today.

• ## Serpentine belts

Many car engines use a serpentine belt, passing across multiple pulleys and tensioner wheels, to transmit mechanical power and timing information from the car’s crankshaft to its alternator, engine fan, water pump, air conditioning, steering pump, and other systems. Another (usually separate) belt, the timing belt, similarly connects the crankshaft to the camshaft, which controls and drives the timing of the engine’s valves. The Volvo bus engine below shows both of these belts:

• ## Footprints in the snow

Given an abstract optimization problem with multiple solutions, how much partial information about a solution do you have to know in order to uniquely identify that solution? That has been the topic of some of my earlier research, on how many creases of an origami folding pattern you have to force to be mountain or valley folds in order to cause the remaining folds to go the way you want. And it’s the topic of my new preprint “Tracking paths in planar graphs” (arXiv:1908.05445, with Mike Goodrich, James Liu, and Pedro Matias).

• Tricolor pyramids ($\mathbb{M}$). In this logic puzzle by @jsiehler, you have to 3-color hexagonal tiles avoiding 2-colored upright triangles. What interests me is not that, but the following: it’s the time-space diagram of a 3-state cellular automaton (with time flowing upward and each cell taking the color that makes the triangle below it work). But turned $120^\circ$ it’s still the time-space diagram of the same automaton! I haven’t seen this sort of CA symmetry before.
• ## Report from CCCG

After WADS, I stayed in Edmonton for CCCG. The two conferences have not always been in the same places, but this year they were co-located, and the plan is to continue that pattern in odd years (when WADS is held). As far as I know there are no plans to move CCCG to Scandinavia for SWAT in the even years.

• ## University of Alberta Botanic Gardens

The WADS excursion was to the University of Alberta Botanic Gardens. Here are a few photos I took there: