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general discussion » Math love

bluet's avatar
15 years ago
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bluet
[lim_x->c f(x) = lim_x->c g(x) in {0, -∞, +∞}]^∃[lim_x->c f'(x)/g'(x)] => lim_x->c f(x)/g(x) = f'(x)/g'(x) is pretty nice. <3
lucas's avatar
15 years ago
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lucas
i ❤ demo
common sense doesn't need a name
bluet's avatar
15 years ago
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bluet
True. And I'm extremely sorry. :(
andre's avatar
15 years ago
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andre
$ xterm -geom 159x100
$ ghci
Prelude> let f = 1 : 1 : zipWith (+) f (tail f) in take 780 f


See anything interesting?

It should work with any language... If you don't have Haskell you could try it in Ruby with

$ irb
irb(main):001:0> def f(n); r = [1,1]; 2.upto(n-1) { |i| r << r[i-1] + r[i-2] }; r; end
irb(main):002:0> f 780


Fibonacci numbers are awesome :)
bsdlite's avatar
15 years ago
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bsdlite
thinks darkness is his ally
> ^∃

i don't understand the notation at all, bluet; is this a statement of l'hospital's theorem?
lucas's avatar
15 years ago
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lucas
i ❤ demo
http://en.wikipedia.org/wiki/Logical_conjunction
http://en.wikipedia.org/wiki/Existential_quantification

yeah, i think it's the theorem.
bluet's avatar
15 years ago
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bluet
It's supposed to be. I attempted to translate Wikipedia's definition with words.
lucas's avatar
15 years ago
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lucas
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is there an operator that means " has the same sign as " ?

one way to do it is this:

ab > 0 <=> "a and b have the same sign"

but i want a cleaner way that looks like this:

a [operator] b
lucas's avatar
15 years ago
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lucas
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the fun way to say "ab > 0" is "a and b are on the same side of zero." it makes me smile. :)
andre's avatar
15 years ago
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andre
I think you could say "a, b > 0".
lucas's avatar
15 years ago
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lucas
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i think "a, b > 0" means "a > 0, b > 0"
andre's avatar
15 years ago
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andre
Isn't that what you meant? It's like saying "both are positive".
andre's avatar
15 years ago
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andre
Oh, I see, "both are negative" should be true too.
andre's avatar
15 years ago
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andre
I guess for clarity you could use "sgn(a) = sgn(b)" where sgn is the signal function.

sgn x | x < 0     = -1
      | x > 0     =  1
      | otherwise =  0
lucas's avatar
15 years ago
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lucas
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:) cool, will do. i might call it "sign()", but "sgn()" is nice because it works for "sign" and "signal."
Fsmart's avatar
15 years ago
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Fsmart
i used the sign() function in my thesis theory section in order to allow for ordinal ranking of outcomes whose expected value is less than zero:). mu is expected return from an outcome. tao is stochastic standard deviation. mu and gamma are preference parameters.

expected utility = U=sign(mu)|mu|^theta-tao^gamma

how impossible would it be to get code that compiled equations in posts to latex dynamically? just thinking it would be pretty awesome.
lucas's avatar
15 years ago
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lucas
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probably not extremely difficult
bluet's avatar
15 years ago
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bluet
Or you could add MathML support.
lucas's avatar
15 years ago
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lucas
i ❤ demo
yeah, i was looking at that, too.