log
(PHP 4, PHP 5)
log — Natural logarithm
說明
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 .
參數
- arg
-
The value to calculate the logarithm for
- base
-
The optinal logarithmic base to use (defaults to 'e' and so to the natural logarithm).
Return值
The logarithm of arg to base , if given, or the natural logarithm.
更新日誌
| 版本 | 說明 |
|---|---|
| Since 4.3.0 | The optinal parameter base became available. For older versions 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. |