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December 14, 2019 Meeting Notes

The December meeting was hosted by Scott Vorthmann. As usual for meetings hosted by Scott, the meeting started off with people socializing and working on a Zometool build. This time, the model in question was a vertex centered projection of a 120-cell. Unlike the cell centered Zometool 120-cell model, this model requires a great number of specialty 3D printed pieces. We were unable to complete the model in the time allotted, but Scott finished it the next day and you can see the completed model below.


There were three talks at the meeting.

Marc Roth spoke on Pascal’s triangle designs and showcased 2 quilts made by Elaine Krajenke Ellison using his Pascal’s triangle designs.



He also shared a Pascal’s triangle mod-10 playing card puzzle, and brought puzzles for everybody to try.

Roger Antonsen spoke about his experience at the ICERM Illustrating Mathematics semester workshop. He shared his semesters worth of concentrated math art work there. This included visualizing card shuffling, various methods of circle packing, a laser cut Hilbert curve Celtic knot, a laser labyrinth mirror Hilbert curve, using tiles to make a Hilbert curve (3 different tiles required), visualizing peg solitaire games, and a beaded cellular automata project that he worked on with Gwen Fisher. On top of all that he also quickly showed assorted works in progress that came out of the ICERM semester workshop.

Lastly, Jeffrey Ventrella gave a Bridges talk rehash on his work on “Portraits from the family tree of plane filling curves“. You can see more of his space filling fractal curves work at his website: or


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November 16th, 2019 Meeting Notes

The November 16th meeting was hosted by Jason Merrill at the Desmos office. There were four presentations.

Indira Chatterji gave a presentation on her mathematical drawings and animations.

Chamberlain Fong presented on “squircles” and the content of his last Bridges paper.

Scott Vorthmann gave a presentation on vZome.

Toby Schachman gave a presentation on his Sun Seeds project with collaborator Ryan Alexander. If you’re interested in purchasing Sun Seed kits, they will continue taking orders while we’re finishing this batch. Please contact Toby if you are interested. More info on the Indiegogo campaign can be found here:

Toby also spoke about Cuttle, the CAD tool he is developing which we used to design the Sun Seeds. Cuttle combines direct-manipulation vector editing with programming capabilities. More info, and a place to sign up for updates:
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September 27th, 2019 Meeting Notes

Cliff Stoll hosted at his home and Klein Bottle warehouse.

Participants were given a tour of the Klein Bottle warehouse and warehouse robot.


He also shared a number of his various mathematical amendments to his home as well as an assortment of mathematical blown glass artwork.

Jacob Rus presented his work on some delightful images that result from accumulations of floating point errors. His “Non-robust arithmetic gallery” can be seen here: This work has since been made into actual fabric with the help and advice of Stacy Speyer, so hopefully we will all get to see at the next meeting.

Nan Ma presented his new website about regular star polytopes: During the walk-through of several webpages with many images and animations, he shared the interesting fact that when you explode cells of the star polytope, the Grand 120-cell to a specific distance, they form the convex 120-cell.

Stacy Speyer brought some examples of her woven balls for show and tell, and Stan Isaacs brought an assortment of puzzles.

Additional images from this meeting can be found here:

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August 10th, 2019 Meeting Notes

Scott Vorthmann organized a build of a zometool “bucky-bone” to start off the meeting. The “bucky-bone” is a model of two C80 bucky balls connected by a carbon nanotube. You can read more about this model here:

Following this, several people shared recent projects. Gwen Fisher taught about her process creating mathematical artwork with colored pencils, and allowed us to try them out. Bruce Puckett gave us a tour of his beautiful mathematical art, all coded in Java, I believe. Stacy Speyer shared her hepta-hexaflexagon project, and Stan Isaacs shared the rolling shapes he acquired from MoMath.

Thank you to all who attended, and thank you to the well-wishers who could not!

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2nd Annual CDG-GDC Palindrome Party

7:07 on March 1st at CDG (sunday evening before GDC)

Come join us for an evening of casual palindromic fun, symmetry, and mathy games. We will walk backwards, listen to reversed music, and drink regal lager.

Price of admission: one palindrome of your own invention, or palindrome-inspire symmetryish thing (mirror symmetry artwork, food with a palindromic name, etc).

Also bring your mathy-arty-inspired games and demos. Feel free to bring friends, but they must bring their own palindrome thing!


Networking policy: In order to keep our sanity, especially in the days surrounding GDC, we ask that no non-consensual networking or business inquiries take place during magical palindromic happy times.

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Hart Art for Valentine’s Day

Join us on February 14th for a special Octahedral Group meeting featuring special guest George Hart ( He will be running a geometric sculpture workshop. This should be a great workshop for math art newbies, so feel free to bring your date!*

What: Hart Art!
When: Saturday, February 14th from 2-6pm

*Newbie-ness and date-ness optional. Everyone should come!

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Topologically Interesting Felt

Math never felt so good.

Come learn how to build mathematical objects made out of felt. Beginner felters and beginner math artists welcome!

You can render your favorite topologically interesting surface using sheep’s wool felted over a scaffold made from fabric or yarn. Möbius-type bands and Seifert surfaces are also nicely represented in felt because handmade felt has no seams, and it’s very strong and flexible. So you can fiddle with and twist your objects into a variety of configurations without the felt tearing.


You can also create “wire” frames like the edges of a hypercube or a hyperbolic tiling.


Gwen Fisher is our resident mathematical felting expert; the above pictures are hers. Materials and tools will be provided.

What: Topologically interesting felt
When: 2-5:30pm on Sunday, January 11th

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Kaleidoscope Party

Sunday the 20th of July at 1pm.

You’re probably familiar with the standard kaleidoscope mirror construction, but there’s so many more possibilities, from different geometries to kinetic kaleidoscope sculpture.

If you like looking at stuff through mirrory mirrors, come see the latest in cutting edge kaleidoscopic technology with special guests Ned Greene and John Edmark, who are bringing physical kaleidoscopes like you’ve never seen before!

We’ll also play with digital kaleidoscopes on the big screen, and do kaleidoscopic audio experiments. There will be beer and oranges. There may be kaleidoscopic video and picture taking. It will also be necessary to create a human kaleidoscope.

If you have a kaleidoscope or something mirrory to share, physical or digital, bring it along! Also bring your friends. This event will be particularly welcoming towards newcomers.

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Slices vs Shadows

June 1st the epic battle between Slices and Shadows commences, and all are invited to witness the carnage.
Who will prevail: the perfect sword of exact yet partial truth, or the shining light that renders complete but warped shadow?
Is it better to completely understand a tiny section of a thing, or to see the big picture but only as an abstraction?
Marc ten Bosch returns with new ways to slice and dice your favorite polytopes, all from the comfort of our couch and his ipad!
On the other side of things, special guest Henry Segerman brings his convincing arguments for stereographic projection with awesome 3d-printed models of 3d and 4d shapes. See projection in action!
Support for projection comes from Andrea Hawksley, whose giant hair tie 120-cell boings in agreement.
But the projection camp, while large, contains inner dissent that threatens to tear them apart! Scott Vorthmann turns against his stereographic-loving colleagues, claiming: “Any right-thinking geometer must prefer orthographic (by definition).”
Whether you know all about slicing and projecting geometric objects or are learning for the first time, come pick a side (the more vitriol the better), and bring something slice or shadow-related for everyone to enjoy. This can be either a mathematical art interpretation, or anything involving the idea of slices or shadows.

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Geometry Party

If you could build anything, what would it be?
A Sierpinski triangle or binary tree?
Would you make a polygon or a polyhedron,
Or ambitiously generate a Zometool polychoron?
Perhaps you’d use cards or bubbles or strings,
To create an abundance of all kinds of things.
For geometric constructions, we have all the elements.
We just need your insight on April the 27th.

Come make geometry with us in SoMa on April 27th from 1-5pm. Bring your favorite geometric building kit or just an idea for something that you’d like to build. We will kick off with a build of a 24-cell (our favorite polychoron with octahedral cells) out of Zometool.

Sign up to learn more!