Caterloopillar

This article is about the adjustable spaceship. For the 17c/45 crawler ship, see Caterpillar.

Caterloopillar
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Pattern type	Spaceship
Number of cells	232815
Bounding box	734 × 514927
Direction	Orthogonal
Period	2000 (mod: Unknown)
Speed	c/8 | 250c/2000
Heat	220775.0
Kinetic symmetry	n
Discovered by	Michael Simkin
Year of discovery	2016
Rules Outer-totalistic rules B3/S23 only # of rules 20 = 1 Isotropic rules B3/S23 only

Caterloopillar is the name given to a family of spaceships which provides a general solution for self-supporting orthogonal travel at a wide range of speeds.

The engineless design is made up of two major parts, the front and the back. In Caterloopillar, each of these parts is a universal constructor that constructs the building blocks of the other part, while also reading and moving a construction tape. As the name suggests, this creates somewhat paradoxical design, similar to the "strange loop" concept.

The Caterloopillar was voted Pattern of the Year for 2016 on the ConwayLife.com forums.

A Golly script is available that can generate spaceships of all supported speeds and lower than c/4. The script does not work for speeds of the form m/(8k+2) and m/(8k+6).

History

The general idea of adjustable speed spaceships was proposed by David Bell in October 2006 on the LifeCA mailing list, and independently by Jason Summers in December 2007. Hartmut Holzwart revived discussion about the idea in September 2014 on the ConwayLife.com forums.

During those discussions, Alexey Nigin in 2014 proposed a novel way of construction that would avoid helices. Instead it would use two streams upward and downward, that create each other using slow salvos. Surprisingly enough the final design of the first Caterloopillar was very close to his description.

Alexey Nigin's initial design proposal was purely theoretical. The first example showing that the idea could be efficiently implemented was found by Michael Simkin a few days after the initial suggestion.

The name was also extensively discussed, with suggestions including strange loop, strange-caterloopillar, pushmi-pullyou and caterloop, finally arriving at Caterloopillar in June 2015.

Implementation

The first Caterloopillar was constructed by Michael Simkin and completed on April 9, 2016; this Caterloopillar has a speed of c/8. Caterloopillars with many other speeds can be constructed using a slightly modified design. The major limitation of this implementation is upper bound of speed c/4, as the signal transferring is done by converting a still life into a glider and back, thus limiting the moving speed of the tape to c/4 (the speed of the glider).

Caterloopillars of various other speeds (see list of spaceships for a full list) were later constructed using the script, the first three being c/9, c/11 and c/12 orthogonal, respectively. One of the most notable Caterloopillars is a 31c/240 one smaller than the Centipede, a previous record holder for that speed which was not based on Caterloopillar technology. It has since been surpassed by the former record holder silverfish and others.

In general, faster Caterloopillars appear to require more cells.

See also

• Caterpillar
• Orthogonoid
• Nora Brown's strictly volatile oscillator family with a similar design

External links

• Caterloopillar at the Life Lexicon
• Caterloopillar WIP (all speeds < c/4) (discussion thread) at the ConwayLife.com forums
• David Bell's engineless caterpillar idea revisited (discussion thread) at the ConwayLife.com forums
• Caterloopillar GitHub repository
• Caterloopillar c/8 RLE file