# 3x3x3 PLL recognition using only two sides



## petero2 (Aug 3, 2009)

I finally decided to learn PLL recognition using information from only two sides. Since I didn't find any computer help for learning this, I decided to implement it myself. (I know about "Drill Sergeant", which is good for practicing recognition + execution, but not perfect if you only want to practice recognition as efficiently as possible.)

I decided to use "Anki", http://ichi2.net/anki/, and I have created two "decks". One deck is called "Rubik's cube PLL decision tree" and helps you memorize the decision tree I use for recognition. The other deck is called "Rubik's cube PLL recognition", and lets you practice recognition for all the 288 possible PLL states.

Example question:





and the corresponding answer:





The images were generated by a quick and dirty python program that I wrote: http://web.telia.com/~u89404340/rubik/pll.py

In case you don't want to use anki, but are still interested in the decision tree, here is a link to a text description. I hope it is understandable:
http://web.telia.com/~u89404340/rubik/pll_decision_tree.txt

I'm sure there are many different ways to create the decision tree, and my way is probably not the best possible way. However, I hope that with enough practice, I will be able to "instantly know" the PLL state without using any concious thinking. When I reach that state, the decision tree will largely become irrelevant.

I'm not there yet though. My average time with my old recognition method (look at all sides and identify blocks) was about 24s. When using 2-side recognition, my median time is currently about 29s.

I also have a question. Together with the 2-side recognition, I also stopped doing cube rotations before the PLL. However, in some cases this means I have to do for example "U + alg + U'" instead of "rotation + alg". Any opinion on which is faster? One cube rotation or two U turns?


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## xXdaveXsuperstarXx (Aug 3, 2009)

> recognition for all the *288* possible *PLL* states.


FAIL..... 21 to be exact.


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## (X) (Aug 3, 2009)

xXdaveXsuperstarXx said:


> > recognition for all the *288* possible *PLL* states.
> 
> 
> FAIL..... 21 to be exact.



Ehhm... 

He is talking about recognizing from different angles so the AUF is calculated into the number. Now I'm not sure if this number is actually 288, but it's certainly *not* 21


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## miniGOINGS (Aug 3, 2009)

I calculated 336 different states.

EDIT: 340 If you're including solved.


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## MTGjumper (Aug 3, 2009)

xXdaveXsuperstarXx said:


> > recognition for all the *288* possible *PLL* states.
> 
> 
> FAIL..... 21 to be exact.




There's a difference between cases and states. Whilst I don't know the actual number, it's definitely greater than 21 (also, you're forgetting solved, which would make 22 by your logic).


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## petero2 (Aug 3, 2009)

MTGjumper said:


> xXdaveXsuperstarXx said:
> 
> 
> > > recognition for all the *288* possible *PLL* states.
> ...



There are 4! = 24 ways to permute the corner pieces, and equally many ways to permute the edge pieces. However, because of corner/edge parity, only half of the possible states are reachable without taking the cube apart. This yields 24*24/2 = 288 PLL states.

However, for recognition, you can immediately cut that down by a factor of 4, by using recognition algorithms that don't use "absolute" colors. That is, you formulate your recognition rules in terms of "relative" colors, for example "if stickers 1,2,3 have one color, stickers 4,5 another color, and sticker 6 a third color, then you have a J permutation".

Also by using mirror symmetry, you can reduce the number of "recognition cases" even more, perhaps down to about 40 (depending on your decision tree and how you count, I suppose).


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## miniGOINGS (Aug 3, 2009)

[offtopic]Using only 6 edge pieces, how many possible permutation states are there? Is it 360?[/offtopic]


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## brunson (Aug 3, 2009)

For your personal amusement:

For PLL recognition I wrote this: http://brunson.com/drillsergeant/

Choose "Use only PLLs, No OLLs" and click "Drill", then try to recognize the case without rotating the cube. If you solve cross on white then you probably want to change the color scheme to ywgbro.


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## Mr Cubism (Aug 3, 2009)

Here are PLL examples only showing two sides.


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## ross mccusker (Aug 4, 2009)

xXdaveXsuperstarXx said:


> > recognition for all the *288* possible *PLL* states.
> 
> 
> FAIL..... 21 to be exact.



yes there are 21 PLL's however

I think he ment all the possible places each PLL can lie. a PLL can lie in 4 possible possitions on the top layer there for can be executed from several different angles. think as a cuber he knows that there are only 21 possible pll cases.

so dont jump in and shout fail just yet!


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## Edmund (Aug 4, 2009)

Im going to learn all these. It should help.


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