Xah Math Blog Archive 2014-10 to 2014-12

how many pieces can you get by cutting a donut 3 times? (you are not allowed to re-arrange the pieces after each cut)

rephrase: Maximal number of regions of dividing a torus with n planes? (n=3 here.)

answer: http://oeis.org/A003600

“group theory” should be called “symmetry theory”

Math Terminology and Naming of Things

Hermitian matrix

In mathematics, a Hermitian matrix (or self-adjoint matrix) is a square matrix with complex entries that is equal to its own conjugate transpose—that is, the element in the i-th row and j-th column is equal to the complex conjugate of the element in the j-th row and i-th column, for all indices i and j.

Hermitian matrices can be understood as the complex extension of real symmetric matrices.

Symmetric matrix

In linear algebra, a symmetric matrix is a square matrix that is equal to its transpose. Example

{
{1, 7, 3},
{7, 4, 5},
{3, 5, 6},
}

Great Math Board Game Software (minor update)

sad to know. Alexander Grothendieck died 2 days ago. Alexander Grothendieck

geometric design on sphere. http://taffgoch.deviantart.com/

pig icosahedron DSC01119
pigs playing icosahedron. 〔photo by Timothy GowersBuy at amazon

old goodie. State of Theorem Proving Systems 2008

sphere lamp projection Wolfram Research
sphere lamp projection, Wolfram Research
Always tampon infinity logo
infinity ∞ found
polyhedron n nekos
Math in Second Life, page 2

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