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 Post subject: Learning Algorithms
PostPosted: Thu Mar 30, 2006 4:04 pm 
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i now have a reasonable knowledge of the F2L, using fridich's algos and my own intuition, so now i am onto learning the LL, i was just wondering how i go about learning them?

the F2L were easy to learn, i could just 'set up' the situation and repeat it until i knew it, but i wouldnt know how to go about 'setting it up' so i couldnt drill the algorithm into my head.

how did you all learn it?

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 Post subject:
PostPosted: Thu Mar 30, 2006 6:35 pm 
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For every algorithm, if you repeat it enough times it will return to solved. So just repeat it till it's solved.
My suggestion would be to learn the PLL before the OLL. If you do it correctly it's really easy to tell. There's never more than three states.

TBTTyler


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 Post subject:
PostPosted: Fri Mar 31, 2006 10:56 am 
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so for example,
if i repeat: L F'L B²L'F L B²L²

on a cube with the top layer solved, it will mess it up and then put it back again eventually?

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 Post subject:
PostPosted: Fri Mar 31, 2006 4:20 pm 
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Absolutely. It may take a while, but it will eventually.
For OLL ... Hmmm maybe 12? Somebody correct me if I'm wrong.
For PLL, you will have to do it no more than 3 times.
Or if you do (F R B L) over and over the cube will eventually solve itself. Took me an hour to do though.

TBTTyler Fox


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 Post subject:
PostPosted: Fri Mar 31, 2006 4:44 pm 
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TBTTyler wrote:
For PLL, you will have to do it no more than 3 times.

U has order 4.


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 Post subject:
PostPosted: Fri Mar 31, 2006 5:37 pm 
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Pembo wrote:
so for example,
if i repeat: L F'L B²L'F L B²L²

on a cube with the top layer solved, it will mess it up and then put it back again eventually?


Yes. On a solved cube L F'L B²L'F L B²L² done three times returns to the solved state. Why didn't you try it yourself?

An algorithm is defined as an operation, that is, a series of elements (movements) that always has the same effect. Things like recipes and methods are also algorithms. The mathematical definition that we are using includes repetitions returning the object to the original state. Note that "series of elements" in this case means multiple turns. Any single turn like U, alone, is not an algorithm.

Cheers,

David J


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 Post subject:
PostPosted: Fri Mar 31, 2006 5:43 pm 
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1. U (yes I mean the single turn) is an algorithm.

2. Repetition returning to identity is not part of the definition of "algorithm".

At least your "we" is wrong since you're pretty much the only person who says so.


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 Post subject: definitions
PostPosted: Fri Mar 31, 2006 7:48 pm 
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Even cursory glances at reputable dictionaries provide one with opportunities to see definitions like this from the American Heritage Dictionary:

> al·go·rithm
n.
A step-by-step problem-solving procedure, especially an established, recursive computational procedure for solving a problem in a finite number of steps. <

If you have difficulty understanding this you can look up the word "recursive," and check for the usage of "plural" in such words as "steps."

Columbia University Press, Houghton Mifflin Dictionary and Wikipedia, among others, agree with me.

Cheers,

David J


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 Post subject:
PostPosted: Fri Mar 31, 2006 9:07 pm 
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I think you're misinterpreting things on purpose. But I'm not gonna play that game.


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 Post subject:
PostPosted: Sat Apr 01, 2006 4:56 am 
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David J wrote:
Why didn't you try it yourself?

i didnt have time, i was leaving the house soon and so i had to pack up my stuff (2 cubes and a game), well i will try them this week and also, i go on holiday a week on tueday, which means i have a whole week to just sit and learn algorithms....what a nice holiday eh?

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 Post subject: algorithm definition
PostPosted: Sat Apr 01, 2006 7:54 pm 
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StefanPochmann wrote:
I think you're misinterpreting things on purpose. But I'm not gonna play that game.


What did I misinterpret? You challenged my definition of algorithm and I gave the references which show that you were wrong.

You wrote that the single turn U is an algorithm, yet most definitions say a step-by-step procedure. Step-by-step procedures contain more than one element. An algorithm has more than one turn.

You say that repetition returning to identity is not part of the definition of "algorithm," yet that recursive aspect is part of what Rubik's cube algorithms do.

And I'm not the only one who says so, in fact I gave you three or four sources which agree with me.

When proven wrong you are incapable of admitting it. Then you have the gall to insinuate that I'm not playing fairly.

This is the third time you've pulled this BS on me and I don't like it. You owe me an apology. I don't think you are man enough to give an honest one. You are like a little boy who gives a book review on a book he's never read, and won't fess up.

You should grow up; until you do, get lost.

David J


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 Post subject:
PostPosted: Sat Apr 01, 2006 10:19 pm 
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"...a problem in a finite number of steps"

I would consider "one" to be a finite number. So an algorithm could consist one step.


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 Post subject: alg remembering
PostPosted: Sun Apr 02, 2006 4:42 pm 
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blogan wrote:
"...a problem in a finite number of steps"

I would consider "one" to be a finite number. So an algorithm could consist one step.


Yes, one is a finite number, but I believe that part of the statement is meant to exclude an infinite number of steps.

Tell me how a single step is a step-by-step procedure.

Cheers,

David J


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 Post subject: Re: alg remembering
PostPosted: Sun Apr 02, 2006 9:35 pm 
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David J wrote:
Yes, one is a finite number, but I believe that part of the statement is meant to exclude an infinite number of steps.

Tell me how a single step is a step-by-step procedure.


Simple, you don't overlap the one step. And I don't think your argument that the finite part is just for excluding infinite doesn't mean that one isn't still valid. You can't argue about the definition and then conviently ignore something if it contradicts what you believe.


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 Post subject:
PostPosted: Sun Apr 02, 2006 9:45 pm 
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I think everyone involved in this thread needs to take a DEEP breath. In-through-the-nose, out-through-the-mouth. Why do we need to be so hostel about a simple little thing like algorithms? There is no need to get flustered when there are FAR worse things to get upset about. If this keeps up, we'll ALL end up with gray hairs! :wink:

Keep it light guys, this is the first thread I've seen to have any ill-will involved. We should try and uphold our position as the cleanest, friendliest forum on the web!

Quinn


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 Post subject:
PostPosted: Sun Apr 02, 2006 9:55 pm 
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i agree with quinn. also go back to the origional question. he wants to know about LL algs. learn the PLL's first they are pretty easy to learn. then move onto OLL's. i learned them from speedcubing but have since relearned some from Leyan Lo's site. you can find it if you go to google and type in his name.


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 Post subject:
PostPosted: Mon Apr 03, 2006 11:50 am 
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i think im going to learn of leyan lo's site, i was looking at it today in school and it looks easier on the eyes,

could someone explain this please:
r2' R2 U' r2' R2 U2' r2' R2 U' r2' R2

what is the lower case 'r' for?

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 Post subject: Re: alg remembering
PostPosted: Mon Apr 03, 2006 1:21 pm 
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blogan wrote:
David J wrote:
Yes, one is a finite number, but I believe that part of the statement is meant to exclude an infinite number of steps.

Tell me how a single step is a step-by-step procedure.


Simple, you don't overlap the one step.


This makes no sense as there is nothing to overlap or not overlap it with.

blogan wrote:
And I don't think your argument that the finite part is just for excluding infinite doesn't mean that one isn't still valid.


I didn't say that it did. I gave that "excluding infinite" as the reason for mentioning "finite" steps. My reasoning against a single step being an algorithm is because of the several terms which make it clear that steps, plural, are required.

"Steps" is plural. A single turn is a finite element with the whole, but it is a part, not the whole definition.

blogan wrote:
You can't argue about the definition and then conviently ignore something if it contradicts what you believe.


That's true, I can't and I didn't. I didn't "conveniently ignore" anything.

You are taking the term "finite" out of context.

David J


Last edited by David J on Mon Apr 03, 2006 1:30 pm, edited 1 time in total.

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 Post subject:
PostPosted: Mon Apr 03, 2006 1:26 pm 
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I'm going to join Stefan in not playing this game.


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 Post subject: Algs
PostPosted: Mon Apr 03, 2006 1:28 pm 
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Quinn Lewis wrote:
I think everyone involved in this thread needs to take a DEEP breath. In-through-the-nose, out-through-the-mouth. Why do we need to be so hostel about a simple little thing like algorithms? There is no need to get flustered when there are FAR worse things to get upset about. If this keeps up, we'll ALL end up with gray hairs! :wink:

Keep it light guys, this is the first thread I've seen to have any ill-will involved. We should try and uphold our position as the cleanest, friendliest forum on the web!

Quinn


Sorry Quinn,

I took myself off one list to keep from butting heads with Stefan, but he continued his hostility here. I don't know what's behind it. I play fair and I argue fair.

You're right I should let it drop.

David J


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 Post subject:
PostPosted: Mon Apr 03, 2006 1:48 pm 
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i dont mean to be rude, but can we stop arguing over the definition of an algorithm, i am not saying i am the greatest person with words ever, but let me try and sum up in one sentence:
algorithm, a sequence of finite moves that can be applied to solve something, (be that mathematical, logical etc,
one turn can be including in the 'steps' arguement, 'steps' used in that sense is a group term and stands for both singular and plural. (this is the only example i can think of: in a game of 5 card draw poker, you may hold some of your cards, that means you may hold 1, 2, 3, 4 or 5 cards.) hope that all made sense

as for my question:
i think im going to learn of leyan lo's site, i was looking at it today in school and it looks easier on the eyes,

could someone explain this please:
r2' R2 U' r2' R2 U2' r2' R2 U' r2' R2

what is the lower case 'r' for?

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 Post subject: games
PostPosted: Mon Apr 03, 2006 1:49 pm 
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blogan,

I was advised not to answer your objection
> I would consider "one" to be a finite number. So an algorithm could consist one step. <
on the grounds that it was deliberately provocative and stupid.

I answered out of respect for you, thinking you were misunderstanding.

blogan wrote:
I'm going to join Stefan in not playing this game.


You should not have joined Stefan in his little game to begin with.

David J


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 Post subject:
PostPosted: Mon Apr 03, 2006 1:55 pm 
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Pembo wrote:
[snip]

could someone explain this please:
r2' R2 U' r2' R2 U2' r2' R2 U' r2' R2

what is the lower case 'r' for?


In some notations lower case means two layers turned simultaneously. In this case 'r2' means the Right side and the middle slice next to it are turned together a half turn clockwise.

In another notation the lower case like 'r' means just the slice so that alg would read r2' U' r2' U2' r2' U' r2'.
This trades 4 edges, each with the edge across the center from it.

David J


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 Post subject:
PostPosted: Mon Apr 03, 2006 2:12 pm 
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thanks, that r stand for right and middle column, i tried r as a slice and it crossed the corners over on the bottom layer

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 Post subject:
PostPosted: Mon Apr 03, 2006 3:03 pm 
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blogan wrote:
I'm going to join Stefan in not playing this game.


Good decision, it's really a waste of time to discuss something with him.

(if you want to read something constructive, jump to (*))

In the early days, I tended to give him the benefit of doubt, thinking maybe he really just misunderstands things. But that benefit is long gone cause he played this game way too often now. My conclusion is that he just likes to be different and play the outlaw and trouble maker to get our attention and time. Some ego trip thing.

Recently in the yahoo group we discussed a probability riddle about some game. He joined it and soon claimed to have won 76 out of 100 games in a simulation. Each had a 1/3 chance of winning, that's probability 0.0000000000000000026 overall. But he told us his "extrasensory perception" capabilities allowed him to do it. He was *not* joking. And he said we (everybody else) are all wrong and we should all just believe him and got all mad. Several people offered opportunities for proof, several people asked for his simulation program. He didn't even bother to refuse, he simply ignored it all. Previous issues had been just as ugly but their contents were somewhat debatable, this one was the first that made it pretty clear what kind of person he is. I think he's the one who should apologize, to the community, for repeatedly misleading, fooling and attacking us.

One sad consequence for me personally is that I can't even fully trust his reasonable stuff anymore, like his knowledge about different cube types or his 3x3 method.

(*) Anyway... to be a little bit more constructive again, if somebody cares what "recursion" really means here: it's when something uses itself, e.g. this algorithm for the factorial function is recursive:
f(n) = if n=0 then 1 else n*f(n-1)

It does *not* mean that any algorithm applied often enough will return the object to the start state again after a while. Imagine you take some unsorted list of numbers. Now apply some sorting algorithm a few times. Do you think it will ever leave the list in the original unsorted order again?

In case of the Rubik's Cube and in the case that an algorithm is a fixed turn sequence, this algorithm does indeed return the cube to the initial state after some number of repetitions. But no sane person would "define" that, cause it can easily be "observed" and thus belongs in a theorem, not a definition.


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 Post subject: reread
PostPosted: Mon Apr 03, 2006 4:51 pm 
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Stefan,

You need to increase your reading skills.

StefanPochmann wrote:
Recently in the yahoo group we discussed a probability riddle about some game. He joined it and soon claimed to have won 76 out of 100 games in a simulation. Each had a 1/3 chance of winning, that's probability 0.0000000000000000026 overall. But he told us his "extrasensory perception" capabilities allowed him to do it.


I never claimed that I did that with ESP. I gave the Rhine experiments as showing *one* of several possible reasons why people do differently than chance "predicts." I made no claim for myself.

StefanPochmann wrote:
He was *not* joking. And he said we (everybody else) are all wrong and we should all just believe him and got all mad.


What I said you guys were wrong about was that you failed to notice that the problem called for *one* trial, not many, and that *none* of the examples given were truly random, but "pseudo-random" constructions. With a truly random thing, like the half life of a lump of radioactive atoms, it cannot be predicted when *one* atom will decay. Switching or not switching in one trial has no effect.

I wasn't mad at Gustav because while disagreeing he kept coming back and acknowledging where I was right; he argued fairly. I wasn't mad at Tyson because he, too, disagreed with respect.

I got mad at you because you posted a private message of mine on a public board, which is a breach of etiquette. I was mad because you made me out to be a liar.

I don't go around making false claims. You look at what I've posted at speedcubing.com's records. How many record have I posted there, and what is the quality of them?

StefanPochmann wrote:
Several people offered opportunities for proof, several people asked for his simulation program. He didn't even bother to refuse, he simply ignored it all.


I didn't bother because you as much called me a liar. With each challenge I met, you failed to acknowledge my answer, and I was issued another challenge. I tired of your being obtuse.

For the ESP-related stuff I gave you publically known experiments, for example, the book "Mind Reach." You gave a "book report" on it without reading the book or doing the experiment. You lack the intellectual honesty which you accuse me of lacking.

On TV there was a Sabado Gigante show on at the end of December. Contestants were to take a key which might win a car from a bowl containing several keys; the host offered to trade $1000 for the key the contestant chose - effectively switching. One lady switched, took the $1000 and lost the car and one lady did not switch and won the car. Reality trumped your mathematical games.

StefanPochmann wrote:
Previous issues had been just as ugly but their contents were somewhat debatable, this one was the first that made it pretty clear what kind of person he is.


Bull.

Sample previous issue: you defined an alg A "easier" than an alg B. You defined easy. I demonstrated that B met your definition of easy. You were unwilling to acknowledge that. The ugliness in my exchanges with you are not on my side. I was doing nothing but defending a point and you attacked me. I responded, yes.

StefanPochmann wrote:
I think he's the one who should apologize, to the community, for repeatedly misleading, fooling and attacking us.


I have never done any of those things.

StefanPochmann wrote:
(*) Anyway... to be a little bit more constructive again, if somebody cares what "recursion" really means here: it's when something uses itself, e.g. this algorithm for the factorial function is recursive:
f(n) = if n=0 then 1 else n*f(n-1)

It does *not* mean that any algorithm applied often enough will return the object to the start state again after a while.


This is a good example of your not reading well. I never said that any algorithm will return the object to the start state again after a while. I guess you missed it above where I wrote,

David J wrote:
Things like recipes and methods are also algorithms.


meaning that I acknowledged that there are algorithms which repeated sufficiently do not return to the original state.

StefanPochmann wrote:
In case of the Rubik's Cube and in the case that an algorithm is a fixed turn sequence, this algorithm does indeed return the cube to the initial state after some number of repetitions. But no sane person would "define" that, cause it can easily be "observed" and thus belongs in a theorem, not a definition.


Shortly after I joined the speedcubing list I called my method an algorithm, and I was informed that sequences of turns were called algorithms in that group and that they differred from a method because repetition returned to the beginning state. I looked it up and acknowledged that both are algorithms.

One other incident with you involved my trying to unify notation because new people were constantly getting confused. I was made out to be some sort of bad guy. You and your friends claiming that I was only out to shove one system down people's throat, like you were looking out for the community.

Nearly a year ago I made a notebook at the speedcubing yahoo group for all the different notations and invited you all to put your notation in it for all newbies. To date none of you have bothered to add your notation to it.

I give you checkable references which you ignore. I meet your challenges and you fail to acknowledge my meeting them. I give up and finally don't meet a challenge and you give me flack.

Like I said earlier grow up. This is 5 aplogies you owe me.

Sheesh!

David J


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 Post subject: Re: reread
PostPosted: Mon Apr 03, 2006 5:18 pm 
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David J wrote:
you posted a private message of mine on a public board


I don't think so.


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 Post subject:
PostPosted: Mon Apr 03, 2006 8:47 pm 
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PLEASE, I BEG OF YOU GUYS, STOP!

Alright, this has seriously gone BEYOND far enough. Whatever issues need to be settled NEED to be settled through one-on-one contact, such as PMs or emails. Demeaning, harshly criticizing, and completely humiliating eachother for the whole forum to see is just completely immature and unneccessary. It doesn't even matter who's right, as there is absolutely no right answer. You two will always see differently, so please, for the sake of the public, leave it at that.

You both are extraordinarily smart, which for the most part is a good thing. It is when situations like these pop up that your intelligence can really hurt you. You know just the right thing to say to hit a nerve in the other person, all for the sake of argument. Well, let me tell you, that gets no one anywhere.

A suggestion to either of the moderators, Wayne or Sandy....delete this thread perhaps? It is the only ugly mark in the history of this forum, heading all the way back to the twistymegasite.com forum. I think it would do us all good to have this site clean again.

Quinn


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 Post subject:
PostPosted: Tue Apr 04, 2006 2:07 am 
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Quinn,

Stefan and Davidj love to do this stuff, I think it's all in good fun. They aren't hurting anyone and besides, it's entertaining. :lol:


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 Post subject:
PostPosted: Tue Apr 04, 2006 7:16 am 
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skeneegee wrote:
it's all in good fun. They aren't hurting anyone

I'm not so sure.

I followed the contentious ESP thread on the yahoo speedsolving message board closely at the time. As he says, David J was careful not to claim ESP abilities when he reported the results of his one-off experiment. Nevertheless, a number of people somehow managed to misinterpret him, which was unfortunate. The discussion became unpleasant.

Everyone here is sensible enough to realize that having the last word in an argument is not the same as winning it. Please just let this one drop and talk about something that's more fun.


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 Post subject:
PostPosted: Wed Apr 05, 2006 11:36 pm 
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I know I'm not making things any better, but the comebacks that you two make are really clever. I think the whole quarrel has challenged all the readers to think for themselves. In a way, I think the argument allows the readers to view both viewpoints (so it's kinda good). If we had more people like you two on a debate team, we would always win. I don't know why I'm writing this, I'm just giving you two khudo's (no, I'm not humiliating or mocking anyone), you guys would make great lawyers (seriously, proofs one after another).

To everyone: Please don't get me wrong, I'm just typing what I'm thinking.

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 Post subject: learning algorithms
PostPosted: Thu Apr 06, 2006 1:45 pm 
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In the spirit of debate I tender the following:

One of the aspects of algorithms is that they *can* be used recursively, that is, repeatedly. In the case where the algorithm is a recipe for apple pie, repetition produces more pies.

Rubik's cube algorithms, in actual use, can also be applied once or repeatedly. For instance, on one level, by applying R U' L' U R' U' L, two corners can be swapped and three corners rotated, or by applying that algorithm twice (R U' L' U R' U' L ) * 2, the order of the corners can be reversed and four of them rotated.
In learning algorithms any one of them can continue to be applied until you reach the starting point, as was properly stated by TBTTyler at the top of this page.

In the realm of computer programs an algorithm can adjust the priority of two things, that is put one before the other, according to some criterion like their relative size. Repetition does indeed allow multiple things to be sorted.

In all of these cases an additional element may be desired - that is an end state. Without an end state you end up with either too many pies, very sore hands, or an infinite loop.

Recursiveness can be part of the definition of algorithms.
Having an end state can be a part of that recursion.
Returning to the beginning state can be that end state.
Therefore: returning to the beginning state can be part of the definition of algorithms.

TA DA! :)

David J


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 Post subject:
PostPosted: Thu Apr 06, 2006 2:06 pm 
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You keep misinterpreting things.


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 Post subject:
PostPosted: Thu Apr 06, 2006 2:33 pm 
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mods, please close this topic already!! :shock:

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 Post subject: Re: reread
PostPosted: Wed Apr 26, 2006 6:33 pm 
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David J wrote:
Bull.


Cow.


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