## This site

The entire site is available a number of ways. As a book:

Doing Physics with Quaternions PDF or EPUB

I am not sure if leanpub is working so well, so here is the pdf or epub.

Put the site on your own computer. At the command line, run:

git clone https://github.com/dougsweetser/Q.git

A collection of 6 problem sets solved using only real-valued quaternions is available for \$1.99 as a pdf, epub, or mobi file

## Bits of this site

1. Space-times-time invariance as gravity in 2 pages - 2 pages
2. Where quaternions fit - 1 page
3. Space-time equivalence classes - 10 pages
4. Space-time Geometries - 1 page
5. Quaternion space-times-time invariance as gravity - 7 pages
6. Deriving the Maxwell source equations by hand - 1 page
7. PGT - Personal Gravity Theory Homework Assignment - 1 page

## Other people's efforts

1. Gauss's notebook - Written in 1819, published 1900, 6 pages. All calculations, no discussion.
2. Sudbery's first paper, "Quaternion Analysis", memo, 1977, 44 pages, on why quaternion analysis is no good.
3. Sudbery's second paper, same title, 1979, 28 pages on the topic. Please look to my work above on quaternion analysis for a much better alternative!.
4. C. A. Deavours paper, "The Quaternion Calculus". My critique is that using his definition of a quaternion derivative, if a function like f=q is analytic in q, f^2 is not. That indicates a better definition must be found before quaternion analysis can really begin.
5. Salamin's paper, "Application of quaternions to computation with rotations", (1979, 9 pages) on rotations. Howell and Lafon's paper, 1975, 13 pages, on the efficiency of quaternion multiplication.
6. Silberstein's paper, "Quaternionic Form of Relativity", 1912, 20 pages, on using biquaternions for quaternion special relativity. Biquaternions are NOT a division algebra, and are not used in any operations on this web site.

## Gimble lock

Resources on gimble lock, a problem that arises from not using quaternions for 3D rotations, links provided by Alex Green:

Bottom line: always avoid Euler angles.