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# log

(PHP 3, PHP 4 , PHP 5)

log -- Natural logarithm

## Description

float log ( float arg [, float base] )

If the optional base parameter is specified, log() returns logbase arg, otherwise log() returns the natural logarithm of arg.

> 注: The base parameter became available with PHP 4.3.0.

> As always you can calculate the logarithm in base b of a number n, but using the mathematical identity: logb(n) = log(n)/log(b), where log is the neperian (or natural) logarithm.

See also exp().

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