@christianp Not sure funding bodies would go for it, but an interesting hybrid would be for people to write, say, $500 or $1000 into their grants to go to arXiv.

@jsiehler Haversine is actually surprisingly useful if you want to smoothly interpolate between \(f(0)=0, f'(0)=0\) and \(f(a)=1,f'(a)=0\).

I also sometimes use the polynomial smoothstep/smootherstep/smootheststep functions: en.wikipedia.org/wiki/Smoothst

Symmetric Minimality

A symmetric minimal lattice trefoil knot, inspired by a conversation here with @11011110, who asked about minimal lattice trefoils with more symmetry and ended up finding the coordinates of this one.

Source code: community.wolfram.com/groups/-


Start with the vertices of the regular icosahedron on the unit sphere. Make circles on the sphere consisting of those points whose spherical distance to one of the vertices is no bigger than \(\frac{\operatorname{arcsec} \sqrt{5}}{3}\). Stereographically project to the plane and this is the result.

Buy it here: shonkwiler.org/store

@11011110 Yeah, that does seem like the right question, doesn’t it?


The Riemann mapping theorem guarantees a conformal map from the unit disk to any simply-connected planar domain; this shows an example of such a mapping to the equilateral triangle.

Buy it: shonkwiler.org/store

@11011110 Nice! That totally works! It’s in Diao’s class (c), but surprisingly it’s not the one he shows. It also looks to me like Scharein et al.’s 2–17 (doi.org/10.1088/1751-8113/42/4), but they don’t remark on it either.

I wonder whether one should expect highly symmetric minimal lattice knots in general; my guess is probably not, but all the evidence seems to suggest that there are lots of minimal examples for each knot type.

@11011110 It’s entirely likely. I just took the one that’s built into KnotPlot, but there are 3496 minimal lattice trefoils (doi.org/10.1007/BF02188227), so I wouldn’t be at all surprised if one is substantially more symmetric. Let me know if you figure it out!

@11011110 Well, that was kind of intentional (and also, being able to see the intermediate frames more clearly wouldn't have helped, because I cheated and just showed projections to the plane with no crossing information).

But, just for you, here are (slightly low res) 3D views of the midpoint between each pause in the animation:


The shortest-possible trefoil knot on the simple cubic lattice.

Source code and further explanation: community.wolfram.com/groups/-

Anne Harding and I made a hand-drawn, hand-cranked version of Truncation (shonk.tumblr.com/post/12997043), showing cross sections of a hypercube.

Check it out in person at the Curfman Gallery (lsc.colostate.edu/campus-activ).

@11011110 At the origami workshop in Barbados? I heard that was very fun.

If I take the tight span of a (convex if you like) n-gon, is there any sensible way of extracting coordinates on n-gon space (as there evidently is for n=3)?

Our paper "Random triangles and polygons in the plane"] – in which we give a novel answer to Lewis Carroll's question "What is the probability a random triangle is obtuse?" – was published recently in the American Mathematical Monthly: doi.org/10.1080/00029890.2019.

Here's an animated version of Figure 2 from the paper, showing a geodesic in triangle space. The geodesic starts at the equilateral triangle shown, and the three curved paths show the tracks of the three vertices.

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