log
(PHP 4, PHP 5)
log — Natural logarithm
Description
float log
( float
$arg
[, float $base = M_E
] )
If the optional base parameter is specified,
log() returns logbase
arg, otherwise log()
returns the natural logarithm of arg.
Parameters
-
arg -
The value to calculate the logarithm for
-
base -
The optional logarithmic base to use (defaults to 'e' and so to the natural logarithm).
Return Values
The logarithm of arg to
base, if given, or the
natural logarithm.
Changelog
| Version | Description |
|---|---|
| 4.3.0 |
The optional parameter base became available.
For older versions you can calculate the logarithm in base b
of a number n, but using the mathematical identity:
logb(n) = log(n)/log(b), where log is the
neperian (or natural) logarithm.
|
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Коментарии
more general version, works fine on negative, very big ($value > 1E+18) and very small ($value < 1E-18) numbers.
function expn($value, $prec = 3, $base = 1000, $prefix = '') {
$e = array('a', 'f', 'p', 'n', 'u', 'm', '', 'k', 'M', 'G', 'T', 'P', 'E');
$p = min(max(floor(log(abs($value), $base)), -6), 6);
return round((float)$value / pow($base, $p), $prec) . $prefx . $e[$p + 6];
}