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What is log ? What does it mean? How does it transform a number?

/I'm a code and see log being used in legacy code I have to change.


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possible duplicate of Intuitive use of logarithms –  t.b. May 9 '11 at 9:03
Have you tried Google / Wikipedia? en.wikipedia.org/wiki/Logarithm –  Qiaochu Yuan May 9 '11 at 9:06
It would help to have a rough idea what the code does. In software, logs are often used for graphing or scoring for instance. –  Oliver Emberton May 9 '11 at 9:29

2 Answers 2

up vote 3 down vote accepted

The base-10 logarithm of a number $x$ is the power that you would need to raise 10 to to get $x$ as a result. For example, since $10^3=1000$, the base-10 logarithm of 1000 is 3.

In general the base-$b$ logarithm of $x$ (written $\log_bx$) is the number you need to raise $b$ to to get $x$. For example, if $b^y=x$ then $\log_bx=y$.

More information: http://en.wikipedia.org/wiki/logarithm

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In addition, the logarithm of a number in a given base roughly reflects one less than the number of digits the number has in that base. For example, in base 10, log 100 = 2 (=3-1 digits)

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