log

(PHP 4, PHP 5, PHP 7, PHP 8)

log — Natural logarithm

Description

log(float $num, float $base = M_E): float

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

Parameters

num: 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 num to base, if given, or the natural logarithm.

Improve This Page

Learn How To Improve This Page • Submit a Pull Request • Report a Bug

＋add a note

User Contributed Notes 1 note

down

-4

c0x at mail dot ru ¶

20 years ago

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];
}