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2.8. Taking Logarithms
2.8.2. Solution
For logs using base e (natural log), use log( ):
$log = log(10); // 2.30258092994
For logs using base 10, use log10( ):
$log10 = log10(10); // 1
For logs using other bases, use pc_logn( ):
function pc_logn($number, $base) {
return log($number) / log($base);
}
$log2 = pc_logn(10, 2); // 3.32192809488742.8.3. Discussion
Both log( ) and log10( ) are defined only for numbers that are greater than zero. The pc_logn( ) function uses the change of base formula, which says that the log of a number in base n is equal to the log of that number, divided by the log of n.
2.8.4. See Also
Documentation on log( ) at http://www.php.net/log and log10( ) at http://www.php.net/log10.
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| 2.7. Generating Biased Random Numbers |  | 2.9. Calculating Exponents |
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