# [Pdx-pm] log base 10

Thomas J Keller kellert at ohsu.edu
Fri Apr 9 12:18:27 CDT 2004

```Hey! I learn a lot from the footnotes and asides people toss in.
and review of first principles is always good.

pdx-pm is a great group. Thanks all.

TjK

On Apr 8, 2004, at 8:15 PM, darthsmily wrote:

> *coughpendanticcough*
> ;)
>
> He didn't specify a language, so I thought I'd be a smart ass and toss
> out some basic code.
>
>
>
> Tkil wrote:
>
>>>>>>> "DS" == darthsmily  <darthsmily at verizon.net> writes:
>>>>>>>
>>
>> DS> Log10 = Log(number) / 2.30258509299405
>>
>> For the people who wonder where the magic number comes from: the
>> logarithm of x in base b can be calculated by dividing the natural log
>> of x by the natural log of b.  In formula form (so far as ascii art
>> allows):
>>
>>           ln x
>>   log x = ----
>>      b    ln b
>>
>> I don't remember enough math to tell you what the appropriate domains
>> would be, but for simple calculations, this should be sufficient.
>>
>> In this case, b is 10, so we have
>>
>>   log10(x) = ln(x) / ln(10)
>>
>> And ln(10) is 2.30258509299404568402, at least according to M_LN10 in
>> /usr/include/math.h.  :)
>>
>> t.
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>>
>>
>
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