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How to do a DNF post-mortem on a non-center piece orbit

cmhardw

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Thread starter #1
Hi everyone,

Looking back on it, I don't think my first post on this method was particularly well written. I believe I made it sound like this method is much harder than it is, when it is so quick and easy to use.

So, here is version 2.0 of the DNF post-mortem method guide. For this guide, I will not list the theory until the very end. This way you can learn how to apply the method first, see how easy it is, then choose to understand the theory only if you want to.

tl;dr
Take the cycles that would solve your scrambled (DNF) cube, and on a solved cube execute those cycles as pre-move before applying the scramble. You must account for any rotations performed on the original (DNF) cube after having applied the scramble and before starting the blindfolded attempt.

Method to quickly do a DNF post-mortem on a non-center piece orbit

Presumably at this point you have just removed the blindfold on your solve, only to open your eyes to a DNF cube :( Don't fret, you will know very shortly exactly what it is that you did wrong. There are 4 steps to this method, all listed below. To be clear too, this method does not really work at all on center piece orbits. You'll have to post-mortem those pieces the old fashioned way.

Step 1) Write down the cycle you would use to solve the DNF state on your cube. Imagine you are memorizing the cube as it is right now for another blindfolded solve.

Step 2) Perform the cycle that you just wrote down twice*

*Follow the asterisk further down for a pro-tip.

Step 3) Perform the scramble again**

**If you did a cube rotation after the scramble, then follow the two asterisks further down for a pro-tip.

Step 4) The cycles you would memorize on the cube after performing the scramble are the cycles you actually executed on the cube during your solve***. Pretty cool huh? :)

*** Pro-tip below

--------------------------------------------

Let's start by doing some examples. All cycles in all of the following examples are given in Speffz

Example 1:

On your solved 4x4x4 perform the following scramble. All lower case letters indicate to turn the single inner slice only. The "w" is the same standard wide-notation used by the WCA.

Scramble: Bw' U2 L' u' L U2 L' u L Bw F' R' u' R U R' u R U' F

Now we are going to memorize this scramble, which would be a pretty sweet scramble to get in the weekly competition ;)

Wings memorization (in Speffz): (A BC DE)

Now remember that we have to DNF this scramble. Let's do this by a common mistake, let's perform the first cycle in the incorrect direction (a common error).

So to "solve" our cube we will perform the following cycles. Follow along on your cube as we go through them.
(A CB) followed by (A DE)

(A CB) = F' R' u' R U R' u R U' F
(A DE) = Bw' L' u' L U2 L' u L U2 Bw

Now we stop the timer, take off the blindfold and OH NOES! DNF :(

Now let's start our DNF reconstruction.

1) Write down the cycle that will solve the DNF state. Our cycle is (B DC)

2) Perform the cycle that will solve the DNF state twice*. To solve the cycle (B DC) we would do:
F' R' u' R U2 R' u R U2 F

Now on our cube, do this alg twice, so do:
F' R' u' R U2 R' u R U2 R' u' R U2 R' u R U2 F

3) Do the scramble again. Looking back our scramble is: Bw' U2 L' u' L U2 L' u L Bw F' R' u' R U R' u R U' F
Do this scramble again on your cube now.

4) The cycles we would memorize to solve the cube as it is now are the cycles we actually did on the scramble. To solve this current state I would memorize:
(A CB DE)

Compare this to the original memorization of:
(A BC DE)

And we immediately see that we did the first cycle in the wrong direction.

Example 2:
Now let's try skipping an image entirely. Start from a solved 4x4x4 cube.

Scramble: Bw' U2 L' u' L U2 L' u L Bw F' R' u' R U R' u R U' F

The cycles we would memorize to solve this cube are:
(A BC DE)

Now, during our solve what if we forgot to execute the BC image entirely (a not as common, but still common mistake). Let's see what happens.

We would "solve" our cube with: (A DE)

(A DE) = Bw' L' u' L U2 L' u L U2 Bw

Now we would stop the timer, remove the blindfold, and open our eyes to a DNF cube :( Let's reconstruct!

1) Write down the cycles that would solve this DNF cube. Our cycle is (B CD)

2) Perform the cycle that would solve the cube twice*. So on your cube do:
F' U2 R' u' R U2 R' u R U2 R' u' R U2 R' u R F

3) Perform the scramble again**. Our scramble was: Bw' U2 L' u' L U2 L' u L Bw F' R' u' R U R' u R U' F
Do this now.

4) The cycles that we would memorize to solve the cube as it is now are the cycles we actually did on the cube during our DNF solve. To solve the cube as it is now we would memorize: (A DE)

Comparing (A DE) to the original memo of (A BC DE) shows us that we did not execute the BC image at all.

Example 3:
Now let's do a completely incorrect cycle during one of our cycles. This would be the same as recalling the wrong image during a solve. From a solved 4x4x4 perform the scramble below:

Scramble: Bw' U2 L' u' L U2 L' u L Bw F' R' u' R U R' u R U' F

We would memorize: (A BC DE) to solve this cube. Let's say that we forget the BC image (Bicycle for me) and while solving we replace it with UI (unicycle for me). Basically you accidentally replace an image with a similar image.

So to solve we will do: (A UI DE) by executing the wrong cycle completely for the first cycle.

(A UI) = U' f' U' F2 U f U' F2 U2
(A DE) = Bw' L' u' L U2 L' u L U2 Bw

Now stop the timer, open your eyes to a DNF state. This is a pretty bad DNF right? Wrong! Let's reconstruct.

1) Write down the cycle that will solve this state. (B CD IU)

2) Perform the cycle that will solve the cube twice. If you haven't already read the pro-tip below, then I'm sorry to say that I will spoil the surprise ;) The following cycle is equivalent to performing our above cycle twice:
(B DU CI)

Read the double asterisk (**) pro-tip below if you don't see how

(B DU) = F R' u' R U2 R' u R U2 F'
(B CI) = Rw U2 F' d2 F U2 F' d2 F Rw'

3) Perform the scramble again. Do this now: Bw' U2 L' u' L U2 L' u L Bw F' R' u' R U R' u R U' F

4) The cycles that we would memorize to solve this state are the cycles we actually performed on the cube. Our memorization here would be: (A UI DE)

Comparing this to the original (A BC DE) we can easily see that we did (A UI) instead of (A BC) for the first cycle. Notice that although this was a small error during the solve, it appeared to be a much worse DNF! That is until we reconstructed it.

--------------------------------------------

Why does this work?

For those interested in the theory of why this method works, please see my original post in the Big Cube BLD Discussion thread.

--------------------------------------------

Pro-tips and footnotes from above

* Actually performing the algorithm twice is a waste of time when you can read the two-times-performed cycle straight from the cycle you wrote down.

Let's look at the cycle (A BC DE). Let's look at what happens at the piece that is currently in the buffer spot A when we perform this cycle twice. The first time through we send A to B. The rest of the pieces in the cycle we don't care about for the moment. Now the second time we cycle this through, the piece that was in A before is now in spot B. When performing the cycle again we will cycle the piece in spot B to spot C.

So performing this cycle twice will move A to C. How many spaces do you notice C is from A in the original written cycle? :)

So if C is two spaces to the right of A, then we can do one equivalent cycle that will be like doing the written cycle twice. Don't cycle the way you normally read, cycle every piece to the place two positions to its right. Remember that once you get to the end, the cycle wraps back around.

So to perform (A BC DE) twice we could just do the following cycle once: (A CE BD)

**You don't actually need to perform the original scramble. It can be difficult to remember what your cube rotation was on a re-oriented solve, not to mention that when you use the actual scramble that the cube ends up scrambled afterward (duh!) and it's hard to follow just the wings, or just the corners in all of that visual noise.

So, my tip is don't perform the scramble. Perform the inverse of what you memorized.

So for example, in the above 3 examples we memorized (A BC DE). Now when I got to step 3 I would not perform the scramble I would perform the inverse of what I memorized, so I would execute the following cycles just like it was a sighted BLD solve:
(A ED CB)

***It's not quite true that what you memorize at the end of this step is really exactly what you executed. What you memorize at this step is an equivalent permutation to what you executed. If you made a setup move error at some point during your solve, then what you memorize at this stage will be an equivalent permutation to what you executed, including the missed/wrong setup turn as part of that permutation. It won't show you the particular setup move that was wrong, only the net effect of how that setup turn combined with the cycles you actually executed.
 
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#4
Same. How many solves do you do a day? Also, how much memory training do you do or does memorizing more just come naturally with more practice? Just wondering.
I do speed cards and randomly memorise numbers whenever I can. (Check out the link on the right of my signature to see my little memorisation thread.) I do about 10-20 full solves a day, along with a practice technique I call Pair-by-Pair. I'm also working on better locations for the method of loci.
 
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#5
I do speed cards and randomly memorise numbers whenever I can. (Check out the link on the right of my signature to see my little memorisation thread.) I do about 10-20 full solves a day, along with a practice technique I call Pair-by-Pair. I'm also working on better locations for the method of loci.
Yea, I've read the method if Loci and have a place, but haven't gotten a chance to try it out yet. How do you memo for 3BLD?
 

cmhardw

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Thread starter #7
This doesn't work too well if you DNF by 1 wrong turn...

(I get 4 corner 4 edges DNFs way too often)
It does not show you the wrong turn, but it shows you cycles that differ greatly from the ones you memorized. Combine that with the structure of the DNF (4 corners and 4 edges) and you can know that the cause of the DNF was that you did 1 wrong turn somewhere during your solve.
 
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