Calculate logarithm in Java

Question

How would I calculate logarithm in Java? How would I extend it to calculate for a sequence? I am trying to find solution for following:-

N different apps have different user growth rates. At a given time t, measured in days, the number of users using an app is g^t .

After how many full days will we have 1 billion total users across the N apps?

Example 1

Input: N = 1, growthRates = [1.5]

output = 52

Example 2

Input: N = 3, growthRates = [1.1, 1.2, 1.3]

output = 79

Have you considered `Math.log()` and friends? Hard to see how this is a duplicate of [this](https://stackoverflow.com/questions/13831150/logarithm-algorithm). — user207421, Nov 09 '20 at 03:24
Does this answer your question? [Logarithm Algorithm](https://stackoverflow.com/questions/13831150/logarithm-algorithm) — pradeexsu, Nov 09 '20 at 03:52

Mustafa Poya · Accepted Answer · 2020-11-09T08:57:17.743

Logarithm in Java

To calculate a common logarithm in Java we can simply use the Math.log10() method:

System.out.println(Math.log10(100));

System.out.println(Math.log(10));

To calculate a logarithm with custom base in Java (log_b(n) = log_e(n) / log_e), we can do it by defining a method as below:

private static double customLog(double base, double logNumber) {
    return Math.log(logNumber) / Math.log(base);
}

a details about mathematic and Logarithm can be found here

1 Answers1