For logarithms to base e
, use
java.lang.Math
’s log( )
function:
// Logarithm.java double someValue; // compute someValue... double log_e = Math.log(someValue);
For logarithms to other bases, use the identity that:
where x
is the number whose logarithm you want,
n
is any desired base, and e
is
the natural logarithm base. I have a simple
LogBase
class containing code that implements
this functionality:
// LogBase.java public static double log_base(double base, double value) { return Math.log(value) / Math.log(base); }
My log_base
function allows you to compute logs to
any positive base. If you have to perform a lot of logs to the same
base, it is more efficient to rewrite the code to cache the
log(base)
once. Here is an example of using
log_base
:
// LogBaseUse.java public static void main(String argv[]) { double d = LogBase.log_base(10, 10000); System.out.println("log10(10000) = " + d); } log10(10000) = 4.0
18.119.131.10