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Analytical logarithms

by joo
Tags: analytic, log
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joo
#1
Jan24-13, 11:57 AM
P: 6
What is the analytical method for solving log. eqs., like x=2^x/14 ?

In highschool they only teach us the graphical approach =/

joo
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jedishrfu
#2
Jan24-13, 12:25 PM
P: 2,977
I suppose you could replace the 2^(x/14) with its taylor series expansion and then cut-off some terms to get an approximation:

http://en.wikipedia.org/wiki/Taylor_series
joo
#3
Jan24-13, 12:37 PM
P: 6
What I meant was x=(2^x)/14, but I guess that doesn't really change the principle.

Thanks, I'll take a look at it, although I find myself doubtful.

0xDEADBEEF
#4
Jan24-13, 01:28 PM
P: 825
Analytical logarithms

There is no analytical solution to your problem. One can express the solutions using the product log function, but that is just another way of writing it, not a true analytic solution.
I like Serena
#5
Jan24-13, 01:31 PM
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Welcome to PF, joo!


In university they still use the graphical approach. ;)

In addition they use approximation algorithms, like the method of Newton-Raphson (which is based on a Taylor series expansion).

It's only the really bold ones in math that use the Lambert W function, which is a function that has only been invented to be able to write the solution to your equation.
As far as I know, no one really uses it.

The first solution for your equation is ##x=-{W(-\frac 1 {14} \ln(2)) \over \ln(2)} \approx 0.07525##.
jedishrfu
#6
Jan24-13, 01:38 PM
P: 2,977
Quote Quote by I like Serena View Post
Welcome to PF, joo!


In university they still use the graphical approach. ;)

In addition they use approximation algorithms, like the method of Newton-Raphson (which is based on a Taylor series expansion).

It's only the really bold ones in math that use the Lambert W function, which is a function that has only been invented to be able to write the solution to your equation.
As far as I know, no one really uses it.
(HUMOR)

But Lambert used it and they made a movie on his life among sheep:

http://www.youtube.com/watch?v=LRtKAQJUc3g

(/HUMOR)
I like Serena
#7
Jan24-13, 02:14 PM
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Quote Quote by jedishrfu View Post
(HUMOR)

But Lambert used it and they made a movie on his life among sheep:

http://www.youtube.com/watch?v=LRtKAQJUc3g

(/HUMOR)
Oh! So the W comes from Walt Disney! :D
joo
#8
Jan24-13, 02:50 PM
P: 6
Thank you for your replies ! I'll stick to the graphical solving for now then, since I will have no access to any calculators during my tests.


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