Math / Logic Discussion

BrickVoid

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Dec 2, 2012
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Oh my god...

I was not kidding about this turning into a math thread.

Please, a moderator (like @Padfoote) do something...

Not only is all this unrelated, I'm supposed to be on school vacation...

Jesus guys have some respect.

If you're not the one making statements about math or logic, why are you worried? Go back to your school vacation while the mathletes competing in this thread let the steam blow off. If you're worried about math homework, I strongly suggest you make sure the homework you've been assigned prior to your vacation is ready to be handed in, whether it's related to math or whatever other subject. If it's got to be done, you have very little time to waste reading this thread, don't you? ;-)

I'm not trying to spoil your vacation, FWIW, I'm just trying to say you have needful things to be reminded of, and should turn your attention to them before it's too late! ;-)

Cheers ...

BrickVoid
 

keybounce

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Hey, this might as well be homework for me. I haven't used formal logic since Grad school, and this is a wake-up / warm-up for me.
 

Type1Ninja

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Hey, this might as well be homework for me. I haven't used formal logic since Grad school, and this is a wake-up / warm-up for me.
Homework - at least by my definition - is forced upon a person. You could totally choose to ignore this, as mentioned above (although you're clearly not doing so :p); myself and @sgbros1 can't just ignore our math homework (well, we can, but that leads to a series of terrible life choices, so let's not be pedantic about "needing" to do certain things). So to say "this might as well be homework" is irksome (understatement for the sake of politeness :p).

On the other hand, I do think that this stuff is cool and can be in this thread (at least for now; padfoote may be right about needing a new thread). I just disagree with the statement "this might as well be homework for me." Carry on, regardless. :p
 

Strikingwolf

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Jul 29, 2019
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Also, I would be writing a reply to @Heliomance and @keybounce's posts, but the problem here is that the forum is derping on long posts, alternatively, I will attempt to formalize the proof using Latex for my things. I have some other things that need to be formalized anyway (some of it logic, some of it's maths like infinite exponentiation [which is awesome, E from k = 1 to infinity of x^k is x^x^(-13/12)]) , so that will probably be fun, that will be going here.
 

keybounce

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Yea, things like "the sum of all positive integers to infinity is a negative fraction" just tells me that our current rules for infinite sums are inconsistent. We need a new Godel to come around and show the flaw.
 

ljfa

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Jul 29, 2019
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We did, it was Cauchy who gave a rigorous definition on convergence and values of infinite series, as well as other calculus stuff ;)

But this definition is not the one that tells you the "the sum of all positive integers" goes to anything but infinity. The partial sums 1, 3, 6, 10, ... get bigger and bigger and not close to -1/12.

But there exist different methods that can be applied to divergent sums to get some value out of them which is kind of like the sum of a series. These methods do not have all the nice properties that you expect from sums of series, but they do have their own sets of rules. It can be surprising and unintuitive ^^

More: https://en.wikipedia.org/wiki/Divergent_series
 

Padfoote

Brick Thrower
Forum Moderator
Dec 11, 2013
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(at least for now; padfoote may be right about needing a new thread)

50 posts seemed to be enough to warrant that IMO, but now at least you all can keep going without limits.

I'm also slightly assumed I was sent the alert that my post was moved when I was the one that moved it.
 

Type1Ninja

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Jul 29, 2019
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... I love how this is now MY THREAD XD

EDIT: Edited my first post with a small history lesson.
 

Strikingwolf

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Jul 29, 2019
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Yea, things like "the sum of all positive integers to infinity is a negative fraction" just tells me that our current rules for infinite sums are inconsistent. We need a new Godel to come around and show the flaw.
There actually is no flaw there, as the result is actually the rieman-zeta function of the sum. It can be used to assign a value to the sum, but it's more like a gold nugget than anything as numberphile says
We did, it was Cauchy who gave a rigorous definition on convergence and values of infinite series, as well as other calculus stuff ;)

But this definition is not the one that tells you the "the sum of all positive integers" goes to anything but infinity. The partial sums 1, 3, 6, 10, ... get bigger and bigger and not close to -1/12.

But there exist different methods that can be applied to divergent sums to get some value out of them which is kind of like the sum of a series. These methods do not have all the nice properties that you expect from sums of series, but they do have their own sets of rules. It can be surprising and unintuitive ^^

More: https://en.wikipedia.org/wiki/Divergent_series
Yeah he said the thing :p
 

Strikingwolf

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An example of what I was talking about as far as the exponentiation thing is concerned

Consider an operator that functions as such, let us call it R for reduce, as the operator is called in programming. R takes a function and a list. The function specifies how the values of the list will be combined in the following manner. Consider f(x, y) R of the list L, in this example this is how the result is defined f(f(f(...f(f(f(first l, second l), third l), fourth l), (l's size - 1) l), last l). Another function is then defined as the map function M, this function is defined as taking a function and a list as well and specifies the values of the list will be transformed. Consider a M applied to list L with function f(x) in the form f(x) M of the list L, here the result is the list {f(first l), f(second l), f(third l)...f((l's size-1) l), f(last l)}. We also define the operator TO which takes two numbers and constructs a list containing them. For example take the numbers n and m, the result will be the list {n, n+1, n+2...m-1, m}

We can then define summation from k = n to m of f(k) as x + y R (f M (n TO m)). We can also define product from k = n to m of f(k) as x * y R (f M (n TO m)). I will now define the RR, or repeat reduce, operator as an operator that takes a function f and applies it to create f R (g M (n TO m)) where n, m, and g are passed into the function.

We now define a new operator E, the exponentiation operator from k = n to m of f(k) as x^y R (f M (n TO m)). This operator takes on a couple of special properties. One of the more useful properties is that it can be expressed in terms of product. The equation for this is such, E from k = n to m of f(k) = f(n) ^ (the product from k = n + 1 to m of f(k)). This follows from the standard exponentiation rules. We can then make a few interesting equations, for one any exponentiation where f(n) = 0 gives 1. We can also say the following, the exponentiation from k = 1 to infinity of x^k = x^(the product from k = 2 to infinity of x^k) = x^((the product from k = 1 to infinity of x^k)/x) = x^(x^(-1/12)/x) = x^x^(-13/12)

the product from k = 1 to infinity of x^k = x^(-1/12) is able to be constructed from the summation of natural numbers being -1/12. as that product is just equal to x^(the summation from k = 1 to infinity of k)
 

BrickVoid

Well-Known Member
Dec 2, 2012
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An example of what I was talking about as far as the exponentiation thing is concerned

Consider an operator that functions as such, let us call it R for reduce, as the operator is called in programming. R takes a function and a list. The function specifies how the values of the list will be combined in the following manner. Consider f(x, y) R of the list L, in this example this is how the result is defined f(f(f(...f(f(f(first l, second l), third l), fourth l), (l's size - 1) l), last l). Another function is then defined as the map function M, this function is defined as taking a function and a list as well and specifies the values of the list will be transformed. Consider a M applied to list L with function f(x) in the form f(x) M of the list L, here the result is the list {f(first l), f(second l), f(third l)...f((l's size-1) l), f(last l)}. We also define the operator TO which takes two numbers and constructs a list containing them. For example take the numbers n and m, the result will be the list {n, n+1, n+2...m-1, m}

We can then define summation from k = n to m of f(k) as x + y R (f M (n TO m)). We can also define product from k = n to m of f(k) as x * y R (f M (n TO m)). I will now define the RR, or repeat reduce, operator as an operator that takes a function f and applies it to create f R (g M (n TO m)) where n, m, and g are passed into the function.

We now define a new operator E, the exponentiation operator from k = n to m of f(k) as x^y R (f M (n TO m)). This operator takes on a couple of special properties. One of the more useful properties is that it can be expressed in terms of product. The equation for this is such, E from k = n to m of f(k) = f(n) ^ (the product from k = n + 1 to m of f(k)). This follows from the standard exponentiation rules. We can then make a few interesting equations, for one any exponentiation where f(n) = 0 gives 1. We can also say the following, the exponentiation from k = 1 to infinity of x^k = x^(the product from k = 2 to infinity of x^k) = x^((the product from k = 1 to infinity of x^k)/x) = x^(x^(-1/12)/x) = x^x^(-13/12)

the product from k = 1 to infinity of x^k = x^(-1/12) is able to be constructed from the summation of natural numbers being -1/12. as that product is just equal to x^(the summation from k = 1 to infinity of k)

Okay, now program that in an actual programming language, compile and run the resulting program, including input and output methods, and see if it actually works like you expect it to. Then post what results you get here. ;-) Theory is one thing but no amount of programming is better than either the output from the debugger or hindsight. ;-)

Cheers ...

BrickVoid
 

Type1Ninja

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Jul 29, 2019
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Okay, now program that in an actual programming language, compile and run the resulting program, including input and output methods, and see if it actually works like you expect it to. Then post what results you get here. ;-) Theory is one thing but no amount of programming is better than either the output from the debugger or hindsight. ;-)

Cheers ...

BrickVoid
I think you miss the point, sir. All of this discussion is strictly theoretical; it deals with things we can only theorize about (stuff like infinity) and has no immediate practical use (you gain nothing by programming it). This is all strictly deductive, no amount of individual examples - as you might get with a program - can prove this. Saying "a computer couldn't do it" misses the point of the proof; even if it IS impossible for a computer to run this, it wouldn't matter, as all of these ideas are just floating around in our thoughts.

But don't be angry, I don't want to start a flame war. :cool: TL;DR: Computers have no bearing on this logical proof.
 

Strikingwolf

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Jul 29, 2019
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Okay, now program that in an actual programming language, compile and run the resulting program, including input and output methods, and see if it actually works like you expect it to. Then post what results you get here. ;-) Theory is one thing but no amount of programming is better than either the output from the debugger or hindsight. ;-)

Cheers ...

BrickVoid
the first two things, reduce and map, are actually very common functional programming concepts ;)

The third thing, repeat reduce as I call it, could be programmed in and you wouldn't die of problems.

All the other things not to do with infinity could be programmed in in fact.

But either way, this is about maths and logic, not really programming
Gosh, that looks awfully convoluted :p
It looks really convoluted because I can't express it in notation, once I write it in LaTeX it will look really nice, because I know from my notebook that it can look better than that shit :p

AKA English isn't very good for expressing maths, maths is
I think you miss the point, sir. All of this discussion is strictly theoretical; it deals with things we can only theorize about (stuff like infinity) and has no immediate practical use (you gain nothing by programming it). This is all strictly deductive, no amount of individual examples - as you might get with a program - can prove this. Saying "a computer couldn't do it" misses the point of the proof; even if it IS impossible for a computer to run this, it wouldn't matter, as all of these ideas are just floating around in our thoughts.
Well, a computer could do this, but you'd have to give it the ability to deduce things from what it knew to solve a problem. So if it knew that the sum of natural numbers is -1/12 and it knew that the product from k = n to m of x^k is equal to x^(the summation from k = n to m of k) then it could get x^(-1/12). At that point you have something that could theoretically replace the grunt of mathematicians work though if it had a broad enough scope :p
 
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keybounce

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I think we need access to the "beyond" from "A Fire Upon The Deep" to really understand those infinite sums.

(just stay away from the "transcend" ...)