# Xah Math Blog

O, math, my true love, how i have alienated thee, and you being quite difficult.

### understand the “expansion” operation on polyhedron

understand the “expansion” process on polyhedron. http://VirtualMathMuseum.org/Polyhedra/Icosahedron/index.html

the term polytope is from mathematician Alicia Boole Stott. Alicia Boole Stott

〔 How real are real numbers? By Gregory Chaitin. At https://arxiv.org/pdf/math/0411418.pdf〕 (local copy How_real_are_real_numbers_By_Gregory_Chaitin_f76de.pdf)

### gyroscopic precession

Learned about gyroscopic precession. Not intuitive. Don't know how the physics works out. But this video is amazing

### Visualize Math with 3D Printing

Visualizing Mathematics with 3D Printing. one expensive book Buy at amazon

### euler's disk

#physics euler's disk. haven't seen this before.

Euler's Disk Buy at amazon

### rattleback

this thing, your spin it, and it spins in reverse direction. Due to built up of instability, the rocking.

rattle back on amazon. Buy at amazon

Math: Density Plots of Trig Expressions. old. repost.

Valentine's Day Gift for a Platonic Relationship: Regular Polyhedrons Chocolates

### Kolam pattern

Kolam (Tamil-கோலம்) is a form of drawing that is drawn by using rice flour/chalk/chalk powder/white rock powder often using naturally/synthetically colored powders in Tamil Nadu, Karnataka, Andhra Pradhesh, Kerala and some parts of Goa, Maharashtra, Indonesia, Malaysia, Thailand and a few other Asian countries. A Kolam is a geometrical line drawing composed of curved loops, drawn around a grid pattern of dots. In South India, it is widely practised by female Hindu family members in front of their houses.[1] Kolams are regionally known by different names in India, Raangolee in Maharashtra, Aripan in Mithila , Hase and Raongoli in Kannada in Karnataka, Muggulu in Andhra Pradhesh, Golam in Kerala etc.,[2] More complex Kolams are drawn and colors are often added during holiday occasions and special events.

[2017-01-12 Kolam]

many more, see https://twitter.com/mariawirth1/status/810098967761616897

logician Raymond Smullyan is 97 now. ☹

Raymond Smullyan is famous among armature mathematicians for his many books on logic, presented as intriguing logic puzzles.

## Knights and Knaves

On a island, all inhabitants are either knights, who always tell the truth, or knaves, who always lie.

John and Bill are residents of the island.

John says: We are both knaves.

Who is what?

here's his books Raymond Smullyan books

### Truly Amazing Euler, Greatest Mathematician. A Intro.

truly amazing Euler, greatest mathematician. Here's his story told by William Dunham, 2008. Save 1 hour to watch.

### Best Introduction to Graph Theory

the best introduction to graph theory is this one.

if you don't know the basics, get it, read it in a week, 1 hour a day. Once you start reading, you can't put it down.

Henry Segerman has been doing amazing things lately.

The story of SageMath. http://wstein.org/papers/talks/2016-06-sage-bp/bp.pdf

excellent story, if you want to know about math software, open source, academia.

here's video version.

### Why is Mandelbrot Set Cardioid Shaped?

more about cardioid here: Cardioid