Difference between revisions of "Domino Reduction"
RedstoneTim (talk  contribs) (Finished speedsolving section) 
RedstoneTim (talk  contribs) (Added more explanations for DR in Fewest move solving) 

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Although Domino Reduction might be viable for speedsolving, it is still not developed enough and too different from other methods to be adapted by more people in the near future.  Although Domino Reduction might be viable for speedsolving, it is still not developed enough and too different from other methods to be adapted by more people in the near future.  
−  == Fewest  +  == Fewest move solving == 
+  Domino Reduction in an [[FMC]] context has been mentioned as early as 2007[https://www.speedsolving.com/threads/fewestmovestipsandtechniques.1566/#post15795]. However, it only started to be widely used in 2019. In that year, Domino Reduction became so popular that it was adopted by virtually all top solvers as their main way to do FMC because it usually yields better results than standard blockbuilding, allowing for consistent sub30 solves in the hands of an expert. The technique also lead to multiple records in that year, such as [[Harry Savage]]'s [https://www.speedsolving.com/threads/harrysavage17fmcsinglesebastianotronto2400mean.72299/ 17 move WR single] [[Sebastiano Tronto]]'s [https://www.speedsolving.com/threads/wrssebastianotronto22meanand16singleatfmc2019.74270/ 16 move WR single]. Inspired by the records and frustrated by the lack of documentation, [[Alexandros Fokianos]] and [[Tommaso Raposio]] documented Domino Reduction for FMC in [https://www.speedsolving.com/threads/adominoreductionguideforfmc.74828/ "A Domino Reduction Guide"] on August 7, 2019. Because the guide explains Domino Reduction in great detail, only an overview is given here.  
+  === Performing Domino Reduction ===  
+  {{work}}  
+  
+  === Finishing after Domino Reduction ===  
+  {{work}}  
+  
+  === Partial Domino Reduction ===  
{{work}}  {{work}}  
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== External links ==  == External links ==  
−  * [https://www.speedsolving.com/threads/adominoreductionguideforfmc.74828/ A Domino Reduction Guide by Alexandros Fokianos and Tommaso Raposio]  +  * [https://www.speedsolving.com/threads/adominoreductionguideforfmc.74828/ A Domino Reduction Guide for FMC by Alexandros Fokianos and Tommaso Raposio] 
* [http://kociemba.org/cube.htm Kociemba's website, including his TwoPhaseAlgorithm]  * [http://kociemba.org/cube.htm Kociemba's website, including his TwoPhaseAlgorithm]  
* [http://kociemba.org/math/distribution.htm Kociemba's distribution of moves required for DR]  * [http://kociemba.org/math/distribution.htm Kociemba's distribution of moves required for DR] 
Revision as of 15:56, 27 June 2020


Domino Reduction or DR is a technique invented by Morwen Thistlethwaite. It is employed by computer algorithms, speedsolvers and fewest move solvers to bring the 3x3x3 cube into a state similar to the Rubik's Domino. This is accomplished by orienting all the corners and performing 2axis EO, reducing the cube from <U,D,L2,R2,F2,B2> to <U,D,L2,R2,F2,B2>. God's number for DR is 12.
Contents
Computer algorithms
Domino Reduction was initially invented to allow computer algorithms to solve the cube efficiently.
The first computer algorithm to utilize Domino Reduction was Thistlethwaite's algorithm in 1981. Due to hardware limitations back then, Domino Reduction is performed in two steps. The algorithm firstly orients the edges and then proceeds to orient the corners and separate the Elayer edges in one step. Using this approach, Domino Reduction can be reached in a maximum of 20 moves. Using two more steps after Domino Reduction, this algorithm was able to solve a cube in a maximum of 52 moves HTM.
11 years later, in 1992, Herbert Kociemba invented Kociemba's Algorithm. It's main difference from Thistlethwaite's algorithm is that the first two steps and the last two steps are combined into one step each, solving the cube in two "phases". Because of this, it is also called the TwoPhaseAlgorithm. It was possible to store all positions using the more advanced technology and various optimizations like symmetry reduction described on Kociemba's website. This algorithm was able to solve Domino Reduction optimally in at most 12 moves and the whole cube in 29 moves.
Speedsolving
Although Domino Reduction is very rarely used in speedsolving, various methods have been invented to allow human solvers to reduce to a domino state quickly.
The first one was Human Thistlethwaite, an adapted version of Thistlethwaite's algorithm for humans, proposed by Ryan Heise in 2002. Most of the reduction steps are either done intuitively or using a small set of premade algorithms. Because of the amount of thinking required and the relatively bad ergonomics of the method, virtually no one uses Human Thistlethwaite as their main speedsolving method.
An unrelated method, Shadowslice Snow Columns, was invented in 2015 by Joseph Briggs. It starts with EOEdge, where edges are oriented and two Eslice edges are solved. The solver then proceeds by building a pseudopair and a pseudotriplet and performing one of 23 algorithms. This solves the last two Eslice edges and orients the corners, effectively reducing the cube to a domino state with all Eslice edges solved. After this step, there are multiple ways to finish. The finish usually has pretty good ergonomics (R2, U, D and M moves) and makes the solve 40 to 50 moves STM long. SSC is a much more viable method for speedsolving than Human Thistlethwaite, although it's still rarely used because it drastically differs from mainstream speedsolving methods and since a good way to finish the cube after DR still needs to be found.
Although Domino Reduction might be viable for speedsolving, it is still not developed enough and too different from other methods to be adapted by more people in the near future.
Fewest move solving
Domino Reduction in an FMC context has been mentioned as early as 2007[1]. However, it only started to be widely used in 2019. In that year, Domino Reduction became so popular that it was adopted by virtually all top solvers as their main way to do FMC because it usually yields better results than standard blockbuilding, allowing for consistent sub30 solves in the hands of an expert. The technique also lead to multiple records in that year, such as Harry Savage's 17 move WR single Sebastiano Tronto's 16 move WR single. Inspired by the records and frustrated by the lack of documentation, Alexandros Fokianos and Tommaso Raposio documented Domino Reduction for FMC in "A Domino Reduction Guide" on August 7, 2019. Because the guide explains Domino Reduction in great detail, only an overview is given here.
Performing Domino Reduction

Finishing after Domino Reduction

Partial Domino Reduction

See also
 Morwen Thistlethwaite
 Corner Orientation
 2axis EO
 Thistlethwaite's algorithm
 Kociemba's Algorithm
 FMC
 Human Thistlethwaite
 SSC
 Half Turn Reduction