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logarithms back to numbers in Excel?

 
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Polly
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Since: Mar 12, 2006
Posts: 9



PostPosted: Tue May 22, 2007 10:46 am    Post subject: logarithms back to numbers in Excel?
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How do I convert logarithms back to numbers in Excel. Log base 10 and natural.
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Bernard Liengme
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Since: Jan 27, 2004
Posts: 2613



PostPosted: Tue May 22, 2007 2:58 pm    Post subject: Re: logarithms back to numbers in Excel? [Login to view extended thread Info.]
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The definition of log (base 10) is:
If x = 10^y then we say LOG(x) =y
Example: 100 = 10^2 so LOG(100)=2
It follows that if I know y and want x I use x = 10^y
If I know the log of x is 2, then x = 10^2 = 100

Likewise:
The definition of LN (base e) is:
If x = e^y (which can also be written as x=EXP(y)) then we say LN(x) =y
Example: 3 = e^1.096 so LOG(3)=1.096
It follows that if I know y and want x I use x = e^y
If I know LN(x) = 1.096 then x = EXP(1.906) which works out to be 3

best wishes
--
Bernard V Liengme
www.stfx.ca/people/bliengme
remove caps from email

"Polly" wrote in message

> How do I convert logarithms back to numbers in Excel. Log base 10 and
> natural.
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Polly
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Since: Mar 12, 2006
Posts: 9



PostPosted: Tue May 22, 2007 2:58 pm    Post subject: Re: logarithms back to numbers in Excel? [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)

Very helpful, thank you Bernard. But is there a function in Excel that I can
use for a column of many figures?


Kind regards
Polly

"Bernard Liengme" wrote:

> The definition of log (base 10) is:
> If x = 10^y then we say LOG(x) =y
> Example: 100 = 10^2 so LOG(100)=2
> It follows that if I know y and want x I use x = 10^y
> If I know the log of x is 2, then x = 10^2 = 100
>
> Likewise:
> The definition of LN (base e) is:
> If x = e^y (which can also be written as x=EXP(y)) then we say LN(x) =y
> Example: 3 = e^1.096 so LOG(3)=1.096
> It follows that if I know y and want x I use x = e^y
> If I know LN(x) = 1.096 then x = EXP(1.906) which works out to be 3
>
> best wishes
> --
> Bernard V Liengme
> www.stfx.ca/people/bliengme
> remove caps from email
>
> "Polly" wrote in message
>
> > How do I convert logarithms back to numbers in Excel. Log base 10 and
> > natural.
>
>
>
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David Biddulph
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Since: Feb 24, 2007
Posts: 1373



PostPosted: Tue May 22, 2007 7:28 pm    Post subject: Re: logarithms back to numbers in Excel? [Login to view extended thread Info.]
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=10^A1 or =POWER(10,A1)
=EXP(A1)
--
David Biddulph

"Polly" wrote in message

> How do I convert logarithms back to numbers in Excel. Log base 10 and
> natural.
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Stan Brown
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Since: Mar 24, 2005
Posts: 531



PostPosted: Wed May 23, 2007 1:01 am    Post subject: Re: logarithms back to numbers in Excel? [Login to view extended thread Info.]
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Tue, 22 May 2007 06:46:01 -0700 from Polly
:
> How do I convert logarithms back to numbers in Excel. Log base 10
> and natural.

=10^A1

=EXP(A1)

--
Stan Brown, Oak Road Systems, Tompkins County, New York, USA
http://OakRoadSystems.com/
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joeu2004
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Since: Apr 16, 2007
Posts: 95



PostPosted: Sun Oct 31, 2010 5:44 pm    Post subject: Re: logarithms back to numbers in Excel? [Login to view extended thread Info.]
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PS: For broader participation, you might want to post future
inquiries using the MS Answers Forums at
http://social.answers.microsoft.com/Forums/en-US/category/officeexcel.
It's not that I like that forum. It's just that MS has ceased to
support the Usenet newsgroups. Hence, participation here is limited
to the sites that share a common newsgroup mirror, which is no longer
centralized at MS.
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Roland Orlie
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Since: Oct 31, 2010
Posts: 1



PostPosted: Sun Oct 31, 2010 7:10 pm    Post subject: Re: logarithms back to numbers in Excel? [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)

i need to know the reverse of a log10 funtion to get back to the number.

> On Tuesday, May 22, 2007 9:46 AM Poll wrote:

> How do I convert logarithms back to numbers in Excel. Log base 10 and natural.


>> On Tuesday, May 22, 2007 9:58 AM Bernard Liengme wrote:

>> The definition of log (base 10) is:
>> If x = 10^y then we say LOG(x) =y
>> Example: 100 = 10^2 so LOG(100)=2
>> It follows that if I know y and want x I use x = 10^y
>> If I know the log of x is 2, then x = 10^2 = 100
>>
>> Likewise:
>> The definition of LN (base e) is:
>> If x = e^y (which can also be written as x=EXP(y)) then we say LN(x) =y
>> Example: 3 = e^1.096 so LOG(3)=1.096
>> It follows that if I know y and want x I use x = e^y
>> If I know LN(x) = 1.096 then x = EXP(1.906) which works out to be 3
>>
>> best wishes
>> --
>> Bernard V Liengme
>> www.stfx.ca/people/bliengme
>> remove caps from email
>>
>> "Polly" wrote in message
>>


>>> On Tuesday, May 22, 2007 10:24 AM Poll wrote:

>>> Very helpful, thank you Bernard. But is there a function in Excel that I can
>>> use for a column of many figures?
>>>
>>>
>>> Kind regards
>>> Polly
>>>
>>> "Bernard Liengme" wrote:


>>>> On Tuesday, May 22, 2007 10:28 AM David Biddulph wrote:

>>>> =10^A1 or =POWER(10,A1)
>>>> =EXP(A1)
>>>> --
>>>> David Biddulph


>>>>> On Tuesday, May 22, 2007 9:01 PM Stan Brown wrote:

>>>>> Tue, 22 May 2007 06:46:01 -0700 from Polly
>>>>>
>>>>> =10^A1
>>>>>
>>>>> =EXP(A1)
>>>>>
>>>>> --
>>>>> Stan Brown, Oak Road Systems, Tompkins County, New York, USA
>>>>> http://OakRoadSystems.com/


>>>>> Submitted via EggHeadCafe - Software Developer Portal of Choice
>>>>> Using the ASP.NET CustomValidator Control
>>>>> http://www.eggheadcafe.com/tutorials/aspnet/e622d48f-2787-4906-b97f-1ef8037a688f/using-the-aspnet-customvalidator-control.aspx
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Ron Rosenfeld
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Since: Jun 01, 2010
Posts: 94



PostPosted: Sun Oct 31, 2010 7:10 pm    Post subject: Re: logarithms back to numbers in Excel? [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)

On Sun, 31 Oct 2010 17:50:09 GMT, Roland Orlie
wrote:

>i need to know the reverse of a log10 funtion to get back to the number.
>


First tell us what happened when you tried the solution in this
message that you quoted, since that should have worked.



>> On Tuesday, May 22, 2007 9:46 AM Poll wrote:
>
>> How do I convert logarithms back to numbers in Excel. Log base 10 and natural.
>
>
>>> On Tuesday, May 22, 2007 9:58 AM Bernard Liengme wrote:
>
>>> The definition of log (base 10) is:
>>> If x = 10^y then we say LOG(x) =y
>>> Example: 100 = 10^2 so LOG(100)=2
>>> It follows that if I know y and want x I use x = 10^y
>>> If I know the log of x is 2, then x = 10^2 = 100
>>>
>>> Likewise:
>>> The definition of LN (base e) is:
>>> If x = e^y (which can also be written as x=EXP(y)) then we say LN(x) =y
>>> Example: 3 = e^1.096 so LOG(3)=1.096
>>> It follows that if I know y and want x I use x = e^y
>>> If I know LN(x) = 1.096 then x = EXP(1.906) which works out to be 3
>>>
>>> best wishes
>>> --
>>> Bernard V Liengme
>>> www.stfx.ca/people/bliengme
>>> remove caps from email
>>>
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joeu2004
External


Since: Apr 16, 2007
Posts: 95



PostPosted: Sun Oct 31, 2010 7:10 pm    Post subject: Re: logarithms back to numbers in Excel? [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)

On Oct 31, 10:50 am, Roland Orlie wrote:
> i need to know the reverse of a log10 funtion to get back to the number.

If A1 contains the result of your LOG10 formula (e.g., =LOG10(1.234)),
then the antilog is =10^A1.

Although that does return exactly 1.234 in that case, in general do
not expect the antilog to exactly equal the parameter of LOG10. For
example, if A1 is =LOG10(PI()), =10^A1-PI()=0 is FALSE(!) [1].

Also, do not expect the antilog to exactly match mathematical
equalities. For example, if A1 is =LOG10(4.5)+LOG10(2) [2], =10^A1=9
is FALSE(!).

Infinitesimal differences are due to the limitations of computer
arithmetic as well as to the fact that generally LOG10 and the power
operator (^) use generating functions or algorithms to approximate
their results (when the exponent is non-integer in the case of the
power operator).

-----
Endnotes

[1] But =10^A1=PI() is TRUE. The difference is due to Excel
heuristics which try to hide inequalities when the difference is
"close" to zero.

[2] We expect LOG10(4.5)+LOG10(2) = LOG10(4.5*2) = LOG10(9) based on
mathematical equalities.
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