24 Aug 2022, 19:24

@hrgdavor I follow up on graph algorithm work I stopped 28 years ago:
https://stamm-wilbrandt.de/en/TR/IAI-TR-93-10.ps.pdf
I built undirected graph library as basis already, it will grow over time. Currently output formats of the tools are SVG, PostScript, and OpenSCAD and JSCAD for sphere embeddings:
https://github.com/Hermann-SW/planar_graph_playground

All planar graphs can be 4-colored (face as well as vertex, faces/vertices sharing an edge have to get different colors), there is a linear time algorithm for 5coloring, and I have built an even simpler 6coloring algorithm: https://github.com/Hermann-SW/planar_graph_playground/blob/main/undirected_graph.js#L311-L332
Yesterday I made 6coloring work for JSCAD sphere embedding, 6coloring for embedding into the plane worked long ago:
https://forums.raspberrypi.com/viewtopic.php?p=2032214#p2032214
6coloring algorithm did use 5 colors only for sphere spherical face coloring (of C60 fullerene) left:
https://www.youtube.com/watch?v=Zl-KumZDBbQ
https://stamm-wilbrandt.de/en/forum/6coloring.spherical_plane.png