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09-04-2008 06:16 PM
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#1
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Super Moderator
Join Date: Jul 2007
Location: Leland Stanford Junior University
Posts: 2,011
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Void Parity Resolution/Algs
The "Void Parity" is the issue that occurs when solving anything equivalent to a 3x3x3, particularly a void cube, where you have odd total parity with your current assignment of centers.
Layer methods hit this (i.e. you can recognize the parity) at PLL, and I think with CF or Roux, you can try to avoid it.
It's well-known that a reassigning centers with a quarter-slice twist + resolving pieces will resolve this. My approach used to be something like an M-fix with a 4-flip and two 3-cycles.
But for speedsolving, you'd want something efficient. Tomas once asked us for a fix in #rubik, and so I got kinda interested.
The most practical is to find a fix that preserves OLL (which can be applied before PLL). It's not hard to imagine that the best fixes are URrML-ish and preserve CPLL, which is also good for CF and Roux, depending on how you do it (and what kind of mistakes you make).
After a while, I found l U r' U M U' M' r U' R' U M U'.
Then, qqwref found the very nice M' U M' U M' U' M' U' M' U2' M' U' M'.
So, does anyone have any other algs, or better approaches?
__________________
Officially the fastest person not using CFOP (Fridrich).
www.garron.us
Last edited by Lucas Garron : 09-04-2008 06:18 PM at 06:18 PM.
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09-04-2008 06:23 PM
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#2
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Premium Member
Join Date: Dec 2007
Location: Dayton, OH, USA
Posts: 1,524
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Y'know what? I used to have a number of these algs, back when I first proposed my "new" 5x5x5 BLD method, but then I never went back to solving a 5x5x5 BLD again, so I think I may have deleted that file (can't find it right now) 
__________________
I'm from Canada, Eastern Kentucky.
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09-04-2008 09:44 PM
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#3
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Member
Join Date: Oct 2006
Location: Malden, MA, USA
Posts: 260
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I've been using the following to swap UF and UR: (M' U')4 (R2 d' M' d2 M' d' R2) (F2 M' F2 M2).
Essentially a 4-flip, an Allan (U-Perm), and an M-layer 3-cycle + M move. But qqwref's alg (which swaps UR and UB after adding a missing U' on the end  ) is shorter.
For swapping UFL and UBR, I've been using (R' U L' U2 R U' L)2 U' F R F' (M' U')4 F R' F' B2 M B2 M2.
Not great algs, but I didn't have to memorize anything new. |
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09-05-2008 12:19 AM
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#4
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Member
Join Date: Apr 2008
Location: Canada
Posts: 135
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My approach to that was to simply do M', then insert the two cross pieces again via the M layer, then orient any edges that were misoriented from doing that.
Ex. M' + U' M' U M U M U2 (M' + M <-- These cancel out) U M U M U2 M' U M' U M' U'
A really inefficient intuitive approach. =\
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09-05-2008 02:40 PM
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#5
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Member
Join Date: Jun 2008
Location: Stockholm, Sweden.
Posts: 75
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M' U M' U' M U' M U2 M' R U R U' M' U R U' r'
edit: joey again
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09-05-2008 08:11 PM
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#6
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Member
Join Date: Oct 2006
Location: Malden, MA, USA
Posts: 260
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Originally Posted by coinman
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M' U M' U' M U' M U2 M' R U R U' M' U R U' r'
edit: joey again
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joey, your alg seems to move a lot of pieces. Did you make a mistake?
BTW, there is this old thread that is somewhat related to this one.
http://www.speedsolving.com/forum/showthread.php?t=2516
(And joey, your alg in that thread doesn't work for me either. Are there people who actually post algs without using an alg checker first?  ) |
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09-05-2008 10:17 PM
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#7
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Super Moderator
Join Date: Jul 2007
Location: Leland Stanford Junior University
Posts: 2,011
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joey's alg is M' U M' U' M U' M U2 (M' R) U R' U' M' U R U' r'. Missed a '.
(And thanks, I know about that thread. I made this thread specifically to discuss approaches to centerless speedsolving, though. )
__________________
Officially the fastest person not using CFOP (Fridrich).
www.garron.us
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09-05-2008 10:25 PM
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#8
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Banned
Join Date: Nov 2007
Location: Brockville, Ontario
Posts: 1,397
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i came up with a really good one for the first opposite swap awhile ago but totally forgot it
Nice alg for 2nd one though from Michael! |
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09-05-2008 11:04 PM
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#9
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Member
Join Date: Feb 2008
Location: New York
Posts: 646
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On the last layer make it so all you have is two edges opposite each other on the layer that need to be swapped. Then do cube rotations so those two pieces are BR and FR. Do E' L2 E L2 E'. The problem with this is that it then leaves you with four edges to orient.
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09-06-2008 06:09 AM
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#10
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Member
Join Date: May 2006
Posts: 2,922
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M' (D' R2 D) (U M' U' M) (D' R2 D)
The M' changes parity, the (conjugated) 5-edges-cycle repairs the damage.
Now with ACube and this input: FD ? -? ? BD DR -? DL FR FL BR BL ? ? ? ? DRF DFL DLB DBR
13 qtm: M' U' B D B U S' U' F' R' B'
9 stm, 12 htm: M' U B2 U2 M' U M U B2
Last edited by StefanPochmann : 09-09-2008 08:29 AM at 08:29 AM.
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