WORKING OUT LOGARITHMS

It's no surprise that Java can handle logarithms, but there's a
surprising gap in the API. Armed with the following information, a 
small barrier
is removed when working with numbers in Java.

Sun's J2SE provides a single log method, double
java.lang.Math.log(double), that is easy to use. The following code:

double x = Math.log(5);

is equivalent to the mathematical equation:

x = ln 5

or

x = log<sub>e</sub>5

where e is the Napierian or natural number.

What if you want a logarithm with a different base? There is no method
available to determine the base-10 log of a number or the base-2 log.
However, both are frequently used in logarithms. The solution is to 
cast your
mind back to school mathematics and the logarithmic equation:

log<sub>x</sub>(y) = log<sub>e</sub>(x) / log<sub>e</sub>(y)

Implement this as a simple piece of Java:

package com.generationjava.math;

public class Logarithm {

static public double log(double value, double base) {
return Math.log(value) / Math.log(base);
}

}

Finding the base-10 logarithm of 100 becomes as simple as:

double log = Logarithm.log(100, 10); // log is 2.0

The base-2 logarithm of 512 is:

double log = Logarithm.log(512, 2); // log is 9.0

The following two simple methods are also useful:

static public double log2(double value) {
return log(value, 2.0);
}

static public double log10(double value) {
return log(value, 10.0);
}

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