Search All of the Math Forum:

Views expressed in these public forums are not endorsed by NCTM or The Math Forum.

Notice: We are no longer accepting new posts, but the forums will continue to be readable.

Topic: Cannot get inverse of y=x/logx to work
Replies: 5   Last Post: May 30, 2011 2:03 PM

 Search Thread: Advanced Search

 Messages: [ Previous | Next ]
 Brad Cooper Posts: 171 Registered: 12/8/04
Re: Cannot get inverse of y=x/logx to work
Posted: May 30, 2011 7:33 AM
 Plain Text Reply

"William Elliot" <marsh@rdrop.remove.com> wrote in message
news:20110529232112.F87371@agora.rdrop.com...
> On Sun, 30 May 2011, Chris Richardson wrote:
>> On Mon, 30 May 2011 15:16:32 +1000, Brad Cooper wrote:
>>

>>> I cannot get the correct result for the inverse calculation of y =
>>> x/log(x).

>>
>> Equations of this type are solvable in terms of the
>> Lambert function:
>>
>> x = -y * W(-1/y), where W is the Lambert function
>>

> W(y) is the solution to y = xe^x; W(y).e^W(y) = y.
>
> You claim -yW(-1/y)/log(-yW(-1/y) = y.
>
> How so?

Hi Chris and William,

Thanks for taking the trouble to reply. I am trying to follow the thread of
the ideas put forward by R. P. Boas Jr.

Are you able to shed any light on why the equation he gives "appears" not to
produce correct results? He was such a great mathematician I am convinced I
have got something wrong, but I simply cannot find where I have made an
error. Some pointers would be greatly appreciated :-)

Cheers,
Brad

Date Subject Author
5/30/11 Brad Cooper
5/30/11 root
5/30/11 William Elliot
5/30/11 Brad Cooper
5/30/11 G. A. Edgar
5/30/11 mjc

© The Math Forum at NCTM 1994-2018. All Rights Reserved.