Logarithm¶
The logarithm is a family of mathematical functions, where log($a * $b) == log($a) + log($b). There are two logarithm functions in PHP: the natural logarithm, where log(M_E) == 1, and the natural logarithm, where log(10) == 1.
PHP also offers log1p($x) == log(1 + $x). This function exists because log($x) is very close to 0 when $x is close to 1. To avoid rounding errors, log1p() is dedicated to this calculations and immediately yields the decimal part of the logarithm.
The opposite function of the logarithm is exponential, exp(), and the ** operator.
A logarithm is not the same as an algorithm, or a log file.
<?php
echo log(M_E);
print PHP_EOL; // 1
echo log(1);
print PHP_EOL; // 0
echo log(1.001);
print PHP_EOL; // 0.00099950033308342
echo log1p(0.001); //0.00099950033308353
print PHP_EOL;
?>
See also PHP Math Functions: A Comprehensive Guide with Examples.
Related : Algorithm, Exponential, Exponent, Floating Point Numbers, zero, one, Log File, E, Log
