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robinhouston

@robinhouston.mathstodon.xyz.ap.brid.gy
128 followers 3 following 866 posts

Maths etc. 🌉 bridged from ⁂ mathstodon.xyz/@robinhouston, follow @ap.brid.gy to interact

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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 07/10/2026
Ha ha ha, the article is 84 pages long and most of them look like this. I don't know what I expected.
A screenshot of page 71 of the article. It is just a long list of lists of three-digit numbers.
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 03/10/2026
You can make it match up perfectly by slightly squashing the octahedra.
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 01/10/2026
A partially disassembled view.
The cluster of 20 magnetic octahedra disassembled into two pieces of different sizes
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 01/10/2026
You can complete it to make a ball of 20 octahedra that don't quite match up perfectly.
A ball of 20 octahedra that don't quite match I perfectly, held in my right hand
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 30/09/2026
Five regular octahedra don't quite make a ring.
Five regular octahedra don't quite make a ring.
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 29/09/2026
I don't know who needs to hear this, but Hanayama have made MASSIVE versions of some of their most iconic puzzles, and you can now get them shipped internationally so you don't even need someone in Japan to forward them. store.hanayamatoys.co.jp/categories…
The MONUMENT cast vortex puzzle on its display standThe vortex puzzle in my hand. It is bigger than my hand.
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 24/09/2026
64 kibisteps
22:16
Today:
Steps
65,533
Distance
54.61Kм
Flights Climbed
29
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 16/09/2026
If this is what it takes to keep the bots out, just let them in. This is too much
An incomprehensible captcha
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 08/09/2026
I wondered whether this was really the minimal unit that tiles by translation, so I just ran a computer search to see if there's a smaller one. And there is! This peculiar-looking 16-unit cluster can also tile by translation.
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 08/09/2026
I knew this shape can fill space, because I had found a cube-like cluster of 64 of them that tiles by translation.
Me holding said cluster in my hand
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 08/09/2026
Long-term followers may remember that I've been interested in this shape, which (rather to my surprise) can fill space.
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 24/08/2026
I assume everyone gets an overpowering urge to say HAIL ERIS when seeing one of these.
A big yellow lorry with the work DISCORDIA written on it in massive red letters
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 23/08/2026
In case I'm not the only person left who prefers to read a paper book rather than an electronic screen, you may be interested to know that the Bridges proceedings are obtainable in physical form.
A copy of the 2026 Bridges proceedings on my kitchen table. The book is thick enough to stun an ox.
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 21/08/2026
“20 yr ago”
Taking the hobbits to Isengard
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 13/08/2026
A screenshot of the explorer, showing ball no. 112 with a Status of “sold”.
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 11/08/2026
Unpacking after Bridges is rather a surreal experience.
A suitcase full of caltrops
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 10/08/2026
Another cool related thing I just found: joris1724 has made a lovely physical model of a genus-41 Stewart toroid, using Zometool with some additional custom 3d-printed parts. joris1724.github.io/vzome-sharing/2…
A photograph of the finished model, taken from the linked page.
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 10/08/2026
Found it. It was posted to Discord on 13 October 2025, as a Stella file. (www.software3d.com/Stella.php)
28
# rf-polytopes
@Robert Webb / Disconnectica Amazing. Never
thought to extract J63s from the existing J63s, but ...
Squilliams 13/10/2025, 17:37
I've also found this alternative genus 291 toroid
based on @the p o kekodjek's 287 (# rf-
polytopes ›•) with 4 extra J63's excavated
from the shell. As far as I know, 291 is the
highest anyone here has found thus far, but l
have to imagine it's possible to do better.
And I'd prefer to remain anonymous, so you
can credit me as 'Squilliams'
genus 291 alt.stel
90.39 KB
1
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 06/08/2026
An interesting effect: photographing this projected screen with my phone camera causes a rainbow effect on the photograph, which isn't visible to the naked eye. Is this a common phenomenon? I don't remember seeing it before.
Henriette-Sophie Lipschuetz gestures at a projected image in a seminar room. The image is strongly rainbow-coloured with a horizontal hue gradient.The projector that is projecting the image in the previous photograph.
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 24/07/2026
Surely someone is missing something here: the woven artefact is clearly a cuboctahedron, and I don't think any wasps make cuboctahedral nests.
A ball woven from dried grass or reeds, resembling a cuboctahedron with the square faces woven and the triangular omitted.A close-up of the label, which reads as follows:

ornament imitating the globular nest of a tree-building wasp. For hanging from house porch: Real combs sometimes hang with them.
(Formerly as traps for spirits).

EASTERN ANGAMI,
LESHEMIE (CHEROMA)
NAGA HILLS, [date obscured]
1.1. J.P. Mills, 1933.
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 20/07/2026
👋🏻 #emfcamp
It's just a pile of tubesEven the 3d-printed model has been dismantled
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 19/07/2026
Is 20 too many stand hours in a day? #emfcamp
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 19/07/2026
Sad. #emfcamp
The EMF Maths Village cuboctahedron lies disassembled on the ground
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 19/07/2026
Achievement unlocked: a puzzle I designed is available commercially from www.nothingyetdesigns.com/products/… (I take no responsibility for that promotional image. It looks like this in assembled form.)
Alhambra in assembled form
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 19/07/2026
A lot of domes coming down today. Sad. On closer inspection, these hub parts look like fibreboard, rather than plywood.
A bucket of laser cut fibreboard parts Another bucket of different laser cut fibreboard parts
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 19/07/2026
Today is your last chance to see #emfcamp
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 18/07/2026
It begins! (Downgraded to 14 disks, following a speed test last night that suggested 16 would take too long.) #emfcamp
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 17/07/2026
This (tomorrow) promises to be an epochal event at #emfcamp.
Electromagnetic Field 2026
Saturday
Marathon Tower of Hanoi solve (16 discs)
09:00 to 17:00 | Maths Village | Performance | Ayliean
MacDonald
Puzzle solving as an endurance sport and performance art piece!
The optimal solution to the classic "Tower of Hanoi" puzzle doubles
in length for every disc added to the tower. Drop by and watch
Ayliean attempt a SIXTEEN DISC tower!! It's going to take all day, so
don't watch the whole thing, but the base disc will only move once
at the half way point - what a highlight to be present for! This is
likely the longest Tower of Hanoi solve that any human has ever
done, but we'll never know and nobody really cares!
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 16/07/2026
Yet another style of geodesic dome hub, this one made from what looks like laser-cut plywood
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 16/07/2026
Three more! (Though two of them bear a distinct family resemblance to one we've already seen.)
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 16/07/2026
Two different styles of geodesic dome hub spotted at @emf so far.
The style of hub where steel tubes are hammered flat at the ends, holes drilled in the flat part, and the ends are overlapped with a bolt through the holesFive struts (plastic tubes) joined using a clever configuration of pipes and cable ties. The struts have a small hole drilled through the end. Each passes through a hole in a large plastic cylinder, about the size of a drainpipe, and is tied around a smaller cylinder with no holes in, concentric with the drainpipe
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 15/07/2026
Come and check it out next to the Maths Village. As well as the nice properties of the colouring, see how to make a lot of equilateral triangles using only right-angled connectors. @emf
A large cuboctahedron made from coloured steel tubes. There are four colours, each forming a regular hexagon. This colouring has the nice consequence that the cuboctahedron's faces exhibit all possible cyclic sequences of three or four colours drawn from the set of 4.
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 15/07/2026
Is there anyone on site at @emf who has anything that could substitute for this missing part? Standard scaffolding tube dimensions (outer diameter 48.3 mm), 90 degree bend.
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 11/07/2026
A nice gimmick at the Escher exhibition in London.
Escher's hand holding a reflective sphere in which, incongruously, you can see my reflection.
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 05/07/2026
Here's a very small clue
A square made by joining four tubes of different colours at their ends
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 03/07/2026
I’ll be interested to see the outcome of the ‘Ramanujan challenge’ www.ramanujanmachine.com/ramanujan-… Conjecture 3.1 is pretty remarkable:
3.1 AN INTEGRAL OVER KNOT POLYNOMIAL ROOTS EXPRESSING 7_2
Let A_{7_2}(M, L) denote the A-polynomial for the prime knot 7_2.

A_{7_2}(M,L) = L^5 + L^4 (M^14 — M^12 + 3M^4 + 4M^2 — 2)
  + L^3 (-2M^18 + 5M^16 + M^14 — 4M^12 + 6M^8 + 5M^6 + 2M^4 — 4M^2 +1)
  + L^2 (M^22 — 4M^20 + 2M^18 + 5M^16 + 6M^14 — 4M^10 + M^8 + 5M^6 — 2M^4)
  + L (—2M^22 + 4M^20 + 3M^18 — M^10 + M^8) + M^22,

Let α ≈ 0.349269... denote the real solution of A_{7_2} (α, α^(1/2)) = 0 closest to 0.349269. Let β ≈ 0.406813... denote the real solution of A_{7_2}(β, β) = 0 closest to 0.406813 Let y = y(z) denote the curve satisfying A(x, y(x)) = 0 for α ≤ x ≤ β and such that y(z) is positive and decreasing with y'(x) ≤ -2. Prove the following formula, which was discovered empirically:

\frac{4 \pi^2}{85} = \int_\alpha^\beta\left(\log x \frac{dy}{y} - \log y\frac{dx}{x}\right)

Context. This result is a surprisingly simple conjectural closed form of a Godbillon—Vey type Knot invariant [Khoi 2008].
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 29/06/2026
I promise I didn't do this – but I note that, if they have to replace the sign anyway, it would be a simple matter to fix the name at the same time.
The top of the MULLER ROUNDABOUT sign broken off and lying on the grass
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 29/06/2026
Masayoshi Son standing in front of an enormous wall covered in mathematical expressions whose significance is unknown to me (and I suspect also to him)
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 29/06/2026
Even the goose theme goes back at least to 2014
A 2014 SoftBank slide reading “Which is more important?” over a picture of five golden eggs and a goose
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 29/06/2026
I worry that in all the excitement about the new SoftBank goose slides, we are neglecting their historical bangers. /fao @pikesley
Masayoshi Son standing in front of an enormous projected slide reading: 25 - 4 = 9 ?
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 25/06/2026
If you want to see what this is going to become, swing by the Maths Village at @emf
A pile of colourful steel tubes and cardboard boxes
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 24/06/2026
Actually, that model is probably quite hard to understand without some explanation. You can think of it as the result of truncating both the pointy vertices of the tetragonal trapezohedron at an angle. So it has eight pentagonal faces, and two trapezia. The […] [Original post on mathstodon.xyz]
The caltrop shown with its convex hull
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 24/06/2026
I noticed that you can turn this into a perfect caltrop by snapping off one of the long spikes. At the time we wrote the paper, we didn’t know very many examples of imperfect caltrops, so I asked whether perhaps _all_ imperfect caltrops might be like this. I […] [Original post on mathstodon.xyz]
A perfect caltrop from a tetragonal trapezohedron truncated at one vertex
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 23/06/2026
One more post before bed: all the examples I’ve shown so far are what I call _perfect_ caltrops, where every spike has the opportunity to point up. Imperfect caltrops also exist. This picture shows one based on the tetragonal trapezohedron: the long axial […] [Original post on mathstodon.xyz]
Tetragonal trapezohedron caltrop
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 23/06/2026
So much for tetrahedra! What other arrangements of spikes might satisfy the caltrop property? Here’s one: it’s a regular pentagonal pyramid. You can probably see how we can do something like this with a pyramid over any regular polygon that has an odd number of sides. (9/?)
Pentagonal pyramid caltrop
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 23/06/2026
It turns out that even the case of tetrahedra is interesting. Not only regular tetrahedra are caltrops, but there are many others. One is shown in this video. Such tetrahedra have been studied since the 18th century, and are known as Orthocentric […] [Original post on mathstodon.xyz]
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 23/06/2026
Caltrops have been used since at least Roman times. This picture shows a Roman caltrop, from Wikimedia Commons at commons.wikimedia.org/wiki/File:Rom… In those days they would presumably have been used to slow a cavalry attack: a charging […] [Original post on mathstodon.xyz]
A Roman caltrop, made of iron
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 23/06/2026
Here is one! Traditionally a caltrop is a cluster of four spikes, arranged like the vertices of a regular tetrahedron. It's a defensive weapon. A defending army can litter the ground with these spikes, which will slow down any attacking force. The caltrop […] [Original post on mathstodon.xyz]
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 10/06/2026
Dome fans will enjoy Spoleto.
A large geodesic dome structure, covering a red-and-white checked paved area, flanked by the entrances to two lifts / elevators.A view of the sky from inside the dome, showing a single pentagonal opening among the triangles
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robinhouston @robinhouston.mathstodon.xyz.ap.brid.gy · 09/06/2026
Can we train a language model to talk like Buckminster Fuller? That would be fun. “locally infinite and inherently indeterminate” “opinionatedly fortified” “omnitriangulated” etc.

OmniTriangulation:
"The sphere is complex unity and the triangle simplex unity.
Here and here alone lie the principles governing finite
solution of all structural and general systems theory
problems, Local isolations of infinite open-ended, plane
and linear edged (seemingly 'flat' anil infinite) segments
of what are, in reality, ¥ast spherical systems-- when taken
out of context-- are hopelessly special-cased, indeterminate
situations.
"Unfortunately engineering has committed itself in the past
exclusively to these locally infinite and inherently
indeterminate systems and have had to rely essentially on
the test proven, local behaviors of small systems such as
columns, beams, levers, et, al,, opinionatedly fortified
with 'safely guesstimated' complex predictions. Not until
we have universal finite, omnitriangulated, nonredundant,
structural system comprehension can we enjoy the advantage
of powerful physical generalizatiogs concisely describing
all structural behaviors,"
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