parity problem without "T" perm ?

[Eaudevian]

hello there
i m quite new in blindfold, and, altought i know how to do a "T" perm to handle with parity problems, i wonder if there is another systematic method to handle with those parity problems, without knowing any perm alg ? :confused:
(maybe the answer is obvious, and its just curiosity, because "T" is not that hard ...)

 

[byu]

Well, if you have odd party, turning a quarter turn fixes it, but I don't know if that's what you're looking for.T isn't the only parity fix. Y, R, J, etc all work

Oh, and this should be in the Blindfold Cubing section.

 

[Eaudevian]

my question was about permutation parity. i know T, Y, J etc. work, but I was wondering if it is possible to avoid using any of them, even if that hypothetical solution would be longer to solve (supposing this solution exists...). i was thinking about commutators or other things for exemple...

this question has no other interest than to avoid memorizing a 14-moves alg such as T.

 

[cmhardw]

my question was about permutation parity. i know T, Y, J etc. work, but I was wondering if it is possible to avoid using any of them, even if that hypothetical solution would be longer to solve (supposing this solution exists...). i was thinking about commutators or other things for exemple...

Well, if you have odd party, turning a quarter turn fixes it, but I don't know if that's what you're looking for.

Brian actually already answered your question, but let me elaborate. Parity is caused because the scramble performs an odd number of quarter turns on the cube. To fix this, you must perform an odd number of quarter turns on the cube, making the total number even.

So, one method to avoid parity, is to memorize the cube as if you have done a quarter turn of the U layer. Remember that actually doing moves on the cube during memorization is instant grounds for disqualification on that solve. So you would have to mentally imagine that you had done a quarter turn of a layer, I recommend the U layer since it would be easy to see and visualize. Then you memorize the cube as normal, only you memorize what the cube will look like after your quarter turn.

After you put on the blindfold you perform that quarter turn you memorized first, then you solve as normal. You will never have a permutation parity on 3x3x3 if you do this.

Practically speaking, most people just use a PLL alg to fix parity. I don't think one of these methods is inherently better or easier than another, it's just that most people use PLL algs. If you were to start right now with that other variation, memorizing as if the cube is off by a quarter turn, then I think that method could be equally as fast if practiced sufficiently.

Hope that helps,
Chris

 

[DavidWoner]

It also depends on your method. If you use M2 and Classic Pochman corners then you can fix parity with U' F2 U M2 U' F2 U. This is way better than using R/T/Y perms etc.

 

[Eaudevian]

thanks all these answers have made things very clear to me!

but, if i use the "one quarter turn of U" method to fix the parity problem, doesn'it means that I must detect the parity before I memorize the cube ? in that case it causes me trouble, because normally I detect the parity at the end of the memorization ! where is my mistake ?

 

[cmhardw]

thanks all these answers have made things very clear to me!

but, if i use the "one quarter turn of U" method to fix the parity problem, doesn'it means that I must detect the parity before I memorize the cube ? in that case it causes me trouble, because normally I detect the parity at the end of the memorization ! where is my mistake ?

You would have to detect parity before memorizing. The way to do this is to quickly trace through the cycles of the pieces without memorizing. Depending on your method you would have to see how many swaps you have to do, i.e. basically use whatever your method does to discover parity, but do it without memorizing pieces. This will tell you whether you have parity or not, and will tell you if you should memorize with or without the single U quarter turn.

The cons of this are that tracing the cycles like this is time lost doing essentially nothing. This is one of the main reason people don't use this method. If you train yourself to do this very quickly, then it can be seen as a memory "primer" for the actual memorization. You would do this tracing on the corners obviously, since there are fewer of them and you could detect parity quicker.

It's all a matter of perspective. Setting up the parity pieces into a PLL sometimes takes time. Tracing pieces for the "memorize with a single quarter turn applied" method takes time as well. It all depends on which method fits your style best.

Chris

 

[AvGalen]

my question was about permutation parity. i know T, Y, J etc. work, but I was wondering if it is possible to avoid using any of them, even if that hypothetical solution would be longer to solve (supposing this solution exists...). i was thinking about commutators or other things for exemple...

this question has no other interest than to avoid memorizing a 14-moves alg such as T.

Parity means you have to switch 2 edges and 2 corners.

Commutators usually just cycle either edges or corners so normally you couldn't solve parity with commutators. (Please don't attack this point, we are dealing with someone that doesn't want to learn 1 14 move T-Perm)

The shortest PLL-alg I know to fix parity is a 10 move J-Perm (very fast as well)

The shortest way to solve parity is by performing 1 quarter-turn. That cycles 4 edges and 4 corners so if you had a parity before the quarterturn it would be gone after it. The easiest way to test this is by doing a J or T-Perm on a 2x2x2. Because there are no edges only 2 corners are swapped (parity). After a U or U' you get a nice 3-cycle of corners (A-Perm). If you would do the same experiment with a 3x3x3 and would just look at the edges (ignore the parity on the corners) you woud notice the same effect (Parity become U-Perm, H-Perm or Z-Perm)

And Chris, analysing before memoing would be a waste in 50% of all cases. Because time is running always I don't think that method would be any good
[off-topic] For 4x4x4 the same system could be used for avoiding parity. 15 seconds inspection is barely enough for this so nobody does it. Also, it is hard and only helps in 50% of all cases[/off-topic]

 

[Eaudevian]

thanks to all, I will try this ! good afternoon

 

[cmhardw]

And Chris, analysing before memoing would be a waste in 50% of all cases. Because time is running always I don't think that method would be any good

True, I agree completely. However I think with training that identifying parity could be done in sub-3 seconds every time. This would mean approximately 3 seconds lost in 50% of cases and 3 seconds lost tracing and approximately 3-4 seconds gained but not executing a parity alg with setups in 50% of cases. I find this to be

0.5 * (3) + 0.5 * (3 - 3.5) = 1.25 seconds increase in your average solving time. I consider this negligible for a beginner/intermediate BLD solver, which I think the poster qualifies for. I don't think any expert would use this method, since it is a net loss of time. However, for most people I think the time lost is negligible.

Chris

 

[AvGalen]

And Chris, analysing before memoing would be a waste in 50% of all cases. Because time is running always I don't think that method would be any good

True, I agree completely. However I think with training that identifying parity could be done in sub-3 seconds every time. This would mean approximately 3 seconds lost in 50% of cases and 3 seconds lost tracing and approximately 3-4 seconds gained but not executing a parity alg with setups in 50% of cases. I find this to be

0.5 * (3) + 0.5 * (3 - 3.5) = 1.25 seconds increase in your average solving time. I consider this negligible for a beginner/intermediate BLD solver, which I think the poster qualifies for. I don't think any expert would use this method, since it is a net loss of time. However, for most people I think the time lost is negligible.

Chris

3 seconds for analysing 20 pieces by a beginner/intermediate BLD solver?
I would need at least 15 seconds to do that (I suck, I know)

 

[Stefan]

Somebody needs to ask the obvious question...

Why?

 

[cmhardw]

3 seconds for analysing 20 pieces by a beginner/intermediate BLD solver?
I would need at least 15 seconds to do that (I suck, I know)

The beauty of it though is that the corner parity matches the edge parity, and you would know this at the scramble. So you can trace the corners only (8 pieces vs. 20) and figure out if the corners alone have parity. If they do, the whole cube does, so you could adjust your memorization accordingly.

I'm at work right now, so I can't try this until I get home, but I'll bet you I can correctly determine parity sub-4 using this method. With sufficient training I think sub-3 would be possible. I am assuming that this would become the beginner/intermediate solver's sole method, and thus they would be getting a lot of practice at doing this.

I'll post an average tonight or tomorrow giving this a try.

Chris

 

[Eaudevian]

0.5 * (3) + 0.5 * (3 - 3.5) = 1.25 seconds increase in your average solving time. I consider this negligible for a beginner/intermediate BLD solver, which I think the poster qualifies for

however, the loss of time should be also depending on the level of the cuber ! I guess I would loose 10s or more, rather than 1.25 .
but the principle of that solution is cool, and it saves moves

 

[Mike Hughey]

3 seconds for analysing 20 pieces by a beginner/intermediate BLD solver?
I would need at least 15 seconds to do that (I suck, I know)

I'm at work right now, so I can't try this until I get home, but I'll bet you I can correctly determine parity sub-4 using this method. With sufficient training I think sub-3 would be possible. I am assuming that this would become the beginner/intermediate solver's sole method, and thus they would be getting a lot of practice at doing this.

I'll post an average tonight or tomorrow giving this a try.

I couldn't resist trying. Here are my results (avg. 10 of 12); (N) = no parity, (P) = parity:
11.55 (P), 36.81 (N), 11.92 (P), 14.89 (N), 14.67 (P), 11.53 (P), (11.25) (N), 11.75 (P), 18.56 (N), 14.05 (P), (DNF) (N but I thought it was P), 13.08 (P) = 15.88.

I would scramble, then determine parity, then stop the timer, then solve all the corners except twisted inactive pieces and/or parity to make sure I was right about the parity. It was good BH corners practice.

Note that I probably lost a few seconds on each solve properly orienting the cube to begin with. I don't think I ever before appreciated how much time I lose in a solve properly orienting even a 3x3x3. It's certainly several seconds.

Chris, I think you're a lot better than me at this. I'm still slow tracing corners by sticker. I've been doing OP for so long, it's a big change to switch to tracing by sticker.

 

[Eaudevian]

it may be obvious, but I remark that there is no need to turn U at the very beginning : it can be done after the orientation step and before the permutation step, so memorizing the orientation can be done as usual (of course I assume the solving method is a beginner method that doesn't imply to orient while permuting ...)

 

[Stefan]

Again: Why? Why do you insist on doing it without a PLL alg? Besides, T perm only needs 11 moves.

 

[AvGalen]

3 seconds for analysing 20 pieces by a beginner/intermediate BLD solver?
I would need at least 15 seconds to do that (I suck, I know)

The beauty of it though is that the corner parity matches the edge parity, and you would know this at the scramble. So you can trace the corners only (8 pieces vs. 20) and figure out if the corners alone have parity....

As Stefan pointed out with just 3 letters, this topic was obviously bad for the brains. How could I have missed such a simple concept :confused:

 

[Eaudevian]

Again: Why? Why do you insist on doing it without a PLL alg? Besides, T perm only needs 11 moves.

maybe for some reason that is similar to the reason why some strange guys want to scramble a multicoloured cube, and rearrange it again and again lol

 

[Mike Hughey]

Again: Why? Why do you insist on doing it without a PLL alg? Besides, T perm only needs 11 moves.

maybe for some reason that is similar to the reason why some strange guys want to scramble a multicoloured cube and rearrange it again and again lol

Exactly! It might be kind of silly to calculate the parity in advance like this, but I have to admit it was kind of fun doing that average of 12 determining parity. I'm really looking forward to seeing Chris's results.