Demonoid

Demonoid
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Pattern type	Spaceship
Number of cells	27250
Bounding box	55010 × 54964
Direction	diagonal
Period	438852 (mod: Unknown)
Speed	65c/438852 | Unknown
Heat	Unknown
Kinetic symmetry	Unspecified
Discovered by	Chris Cain
Year of discovery	2015
Rules Outer-totalistic rules B3/S23 only # of rules 20 = 1
Glider synthesis Fewest gliders 12016† Uploaded synthesis RLE demonoid_synth.rle †Can be constructed with 15 gliders using the reverse caber tosser universal constructor.
Pattern files Macrocell demonoid.mc

Demonoid is the first self-constructing diagonal spaceship in the Conway's Life rule, completed by Chris Cain in 2015. It displaces itself by 65 cells diagonally every 438,852 generations. Its name is an accidental portmanteau of "diagonal" and "Geminoid" by Paul Chapman in February 2013.

Similar to the original Gemini spaceship, the Demonoid consists of two identical halves. Where the Gemini's halves are simple translations of each other, each half of the Demonoid is a glide-reflected mirror image of the other. A tape of gliders continually relays between the two halves, instructing each to construct a daughter configuration.

In the smallest "0hd Demonoid" each half is itself made up of two identical parts made up of a combined 180-degree reflector and edge shooter. A cycle is completed when one of these parts is constructed ahead of the spaceship and an identical reflector/edge shooter is destroyed at the back end as soon as its construction work is done, using a glider completely independent of the rest of the spaceship that triggers a precisely timed self-destruct mechanism.

Demonoids are the smallest self-constructing or self-supporting spaceships in terms of population, but the bounding box of the centipede is about half the size of the smallest Demonoid's, and the waterbear is considerably smaller in both longest diameter and bounding box.

Demonoid variants make up the nineteenth and twentieth explicitly-constructed spaceship velocities, but as with previous self-constructing spaceships they actually represent an infinite family of related velocities. The 0hd Demonoid travels at 65c/(438852+8N) diagonally. Theoretically speaking, a Demonoid spaceship could be designed with any velocity slower than about c/100 diagonally. However, any speed faster than 65c/438852 would require the Demonoid's circuitry to be completely redesigned, with much a much larger total size and population in most cases.

History

The first Demonoid designs were significantly larger and more complicated than the final 10hd or 0hd models. Some early designs required all elbow operations to be made from pairs of gliders, with no singleton gliders allowed.

This allowed the gliders in each pair to be coded on a single tape, one directly after the other. However, it greatly increased the amount of timing circuitry needed. It also cut the allowable signal density in half. IThe signal density was already low because in 2012 the repeat rate for stable Spartan circuitry was 497 ticks or more.

A sizable improvement involved moving to a design with the two halves of the recipe encoded in series instead of interleaved. This allowed for better signal density, and also any combination of singleton gliders and glider pairs.

These early designs were all 9hd -- the two construction lanes were separated by 9 half diagonals, and a block centered between the lanes served as the elbow. This allowed all elbow operations to be used either directly or in mirror-image, which meant that gliders could be fired either left or right from the elbow, and elbow moves could be mirrored if there was limited space available and the move recipe had a larger spark on one side than on the other.

After the 9hd linear propagator was completed, it became clear that 10hd was significantly more efficient, in part because it allowed for two block elbows in slightly different positions between the construction lanes.

The 10hd and 0hd Demonoid both use a much larger number of elbow locations. A library of thousands of elbow operations allows easy switching between different elbow types, and gliders can be output on any nearby lane by stringing recipes together.

The 10hd Demonoid was the first complete self-constructing diagonal spaceship. Its construction recipe encoded two complete 180-degree reflector/edge shooter components, which were mostly identical to each other but had significant differences near the construction lanes. It included complex machinery that blocked the construction lanes during the half of the Demonoid's cycle when the recipe gliders intended for one circuit were passing through the other circuit's reflector.

The 0hd Demonoid improved on the 10hd model by removing the blocking mechanisms and the resulting long pause in construction. Instead, the two reflector/edge shooter components were designed to be completely identical. Each newly constructed component would first produce the trailing halves of the glider pairs in the next construction recipe. Then the same edge shooter would fire the leading halves of the glider pairs for the following construction.

See Also

• Replicator
• Geminoid
• Centipede
• Waterbear
• Half-baked knightship