switch engine

switch engine (plural switch engines)

1. A switcher or shunter: a railroad locomotive used for shunting.
2. (cellular automata) A particular methuselah in Conway's Game of Life that temporarily exhibits glide reflection symmetry while leaving debris behind, allowing for the construction of spaceships, puffers, and rakes.
   • 1990 May 17, David Moews, “Life questions”, in comp.theory.cell-automata‎ (Usenet):

     2. Is it possible to make the switch engine leave debris other than the normal 8 blocks/288 generations?

   • 1992 August 13, David Bell, “Spaceships in Conway's Life (Part 1)”, in comp.theory.cell-automata‎ (Usenet):

     He did this by placing a large number of switch engines together so as to eliminate all debris. His original ship required 13 switch engines, but his smaller one given here only uses 10 of them.

   • 2007 May 12, Dave Greene, “Wanted: 2D CA, "as complex" but "denser" than Life”, in comp.theory.cell-automata‎ (Usenet):

     The average random Life pattern settles down instead of exploding (if you ignore output gliders and spaceships). There are exceptional quadratic-growth cases, mostly involving switch engines, but most random patterns affect only their immediate area.