2.7.1. ProblemYou want to take the logarithm of a number. 2.7.2. SolutionFor logs using base e (natural log), use log( ): $log = log(10); // 2.30258092994 For logs using base 10, use log10( ): $log10 = log10(10); // 1 For logs using other bases, pass the base as the second argument to log( ): $log2 = log(10, 2); // 3.3219280948874 2.7.3. DiscussionBoth log( ) and log10( ) are defined only for numbers that are greater than zero. If you pass in a number equal to or less than zero, they return NAN, which stands for "not a number." 2.7.4. See AlsoDocumentation on log( ) at http://www.php.net/log and log10( ) at http://www.php.net/log10. |