# Haystack Situations

Haystack Situation #20230126

Haystack Situation #20230125 Haystack Situation #20230124 Haystack Situation #20230123

Haystack Situation #20230122 Haystack Situation #20230121 Haystack Situation #20230120

Find the needle in a new icosahedral haystack each day:

mathr.co.uk/haystack-situations

The newest few (at the top) have PDFs, click the thumbnails to download.

RSS feed (like a podcast, but for PDFs):

Algorithmic artwork online since December 2013.

# 1 Implementation Notes

Main program written in the C programming language.

Web pages (HTML, RSS) generated by a Shell script.

Pseudo-random number generator: GNU Scientific Library.

Vector graphics: Cairo Graphics Library.

Sewing needle: based on public domain openclipart by ginger coons.

Typography: Latin Modern Sans 10.

Algorithms: normalized 3D vectors (representing points on a sphere), icosahedral symmetry group (array of 60 3D rotation matrices), stereographic projection from 3D to 2D (with case analysis to handle pole crossings), spherical linear interpolation (SLERP), …