You want to take the logarithm of a number.
For logs using base e (natural log), use log():
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// $log is about 2.30258 $log = log(10); |
For logs using base 10, use log10():
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// $log10 == 1 $log10 = log10(10); |
For logs using other bases, pass the base as the second argument to log():
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// log base 2 of 10 is about 3.32 $log2 = log(10, 2); |
Both 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.
