[MATH-843] Precision.EPSILON: wrong documentation

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 3.0
• Fix Version/s: 3.1
• Labels: documentation
• Assignee: Unassigned
• Reporter: Dominik Gruntz
• Created: 07/Aug/12 19:13
• Updated: 04/Mar/13 18:53
• Resolved: 20/Aug/12 07:56

Description

The documentation of the Field EPSILON in class org.apache.commons.math3.util.Precision states, that EPSILON is the smallest positive number such that 1 - EPSILON is not numerically equal to 1, and its value is defined as 1.1102230246251565E-16.

However, this is NOT the smallest positive number with this property.

Consider the following program:

public class Eps {
  public static void main(String[] args) {
    double e = Double.longBitsToDouble(0x3c90000000000001L);
	double e1 = 1-e;
	System.out.println(e);
	System.out.println(1-e);
	System.out.println(1-e != 1);
  }
}

The output is:

% java Eps
5.551115123125784E-17
0.9999999999999999
true

This proves, that there are smaller positive numbers with the property that 1-eps != 1.

I propose not to change the constant value, but to update the documentation. The value Precision.EPSILON is
an upper bound on the relative error which occurs when a real number is
rounded to its nearest Double floating-point number. I propose to update
the api docs in this sense.