Demonoid
Demonoid  
View static image  
Pattern type  Spaceship  

Number of cells  27250  
Bounding box  55010×54964  
Direction  Diagonal  
Period  438852  
Mod  Unknown  
Speed  65c/438852  
Heat  Unknown  
Discovered by  Chris Cain Dave Greene  
Year of discovery  2015  
 
 

Demonoid is the first type of selfconstructing diagonal spaceship in the B3/S23 rule. A small "0hd Demonoid" was completed by Chris Cain in December 2015, shortly after a much larger 10hd version constructed in November^{[1]} in collaboration with Dave Greene. The 0hd spaceship displaces itself by 65 cells diagonally every 438,852 generations. As of 2018 it is the only case where a spaceship gun pattern was completed before the actual spaceship  the first 0hd Demonoid was fired by a gun.^{[2]}
The name "Demonoid" is an accidental portmanteau of "diagonal" and "Geminoid" by Paul Chapman in February 2013. "0hd" and "10hd" refer to the number of halfdiagonals separating the two glider lanes in the spaceships' construction arms.
Contents
Design
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 glidereflected mirror image of the other. A tape of gliders continually relays between the two halves, instructing each to construct a daughter configuration.
In the 0hd Demonoid, each half is itself made up of two identical parts. Each part consists of a syringebased 180degree reflector combined with an edge shooter, plus a scatteriing of selfdestruct circuitry. 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.
Selfdestruct mechanism
The selfdestruct sequence is triggered by a glider that follows the construction recipe on a slightly different lane. The only output of the cleanup reaction is another trigger glider, which appears in the exact same location as the original trigger glider, relative to the end of the recipe stream.
Statistics
Demonoids are the smallest known selfconstructing or selfsupporting spaceships in terms of population, but the bounding box of the centipede is about half the size of the smallest Demonoid's bounding box, and the waterbear is considerably smaller in both longest diameter and bounding box.
Demonoid variants make up the nineteenth and twentieth explicitlyconstructed spaceship velocities, but as with previous selfconstructing spaceships they actually represent an infinite family of related velocities. If the two halves of the Demonoid are moved N cells farther away from each other, the 0hd Demonoid travels diagonally at a speed of 65c/(438852+8N).
Speed limit
Theoretically speaking, a Demonoid spaceship using the current 0hd elbowmove library could be designed with any velocity slower but not equal to 17c/792 diagonally, or roughly c/47  much faster than the old Gemini limit of c/580^{[3]}. A 0hd elbow can be programmed to move much faster than a Gemini elbow's speed limit of one diagonal cell per coded instruction, and signals in syringebased Herschel circuitry can be compressed to within 90 ticks of each other. However, any speed faster than 65c/438852 would require the Demonoid's circuitry and construction recipes to be completely redesigned, with 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.^{[4]}
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. The 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.^{[5]}
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 mirrorimage, 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 selfconstructing diagonal spaceship.^{[6]} Its construction recipe encoded two complete 180degree 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
References
 ↑ Chris Cain (December 6, 2015). "Re: Demonoid (diagonal Geminoid) completed!". ConwayLife.com forums. Retrieved on December 7, 2015.
 ↑ Chris Cain (December 7, 2015). "Re: Demonoid (diagonal Geminoid) completed!". ConwayLife.com forums. Retrieved on January 4, 2016.
 ↑ "Universal Constructor Based Spaceship". Retrieved on May 21, 2010.
 ↑ Dave Greene (December 22, 2012). "Re: Geminoid Challenge". ConwayLife.com forums. Retrieved on December 8, 2015.
 ↑ Dave Greene (February 15, 2013). "Re: Geminoid Challenge". ConwayLife.com forums. Retrieved on December 8, 2015.
 ↑ Dave Greene (November 25, 2015). "Re: Demonoid (diagonal Geminoid) completed!". ConwayLife.com forums. Retrieved on December 8, 2015.
 Patterns
 Patterns with 1000 or more cells
 Patterns found by Chris Cain
 Patterns found by Dave Greene
 Patterns found in 2015
 Patterns that can be constructed with 1000 or more gliders
 Spaceships
 Spaceships with period 438852
 Diagonal spaceships
 Spaceships with speed 65c/438852
 Glide symmetric spaceships
 Nonmonotonic spaceships