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Date: Thu, 20 Sep 2012 19:15:07 +1100 (NCT)
From: "Yannick TANGUY (JIRA)" <jira@apache.org>
To: issues@commons.apache.org
Message-ID: <186753565.101386.1348128908045.JavaMail.jiratomcat@arcas>
Subject: [jira] [Created] (MATH-866) New method to compute relative
 deviation between two floating numbers
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Yannick TANGUY created MATH-866:
-----------------------------------

             Summary: New method to compute relative deviation between two floating numbers
                 Key: MATH-866
                 URL: https://issues.apache.org/jira/browse/MATH-866
             Project: Commons Math
          Issue Type: Improvement
    Affects Versions: 3.1
            Reporter: Yannick TANGUY


A new method to compute a relative deviation would be very useful.

In order to handle properly odd values (O+,0-,NaN,Infinity), we suggest to call first the classical equals() method (strict equality, using one ulp as a threshold) and then the relative tolerance.

Here is the code we use : 

  public static boolean equalsWithRelativeTolerance(final double x, final double y, final double eps) {

        // Initialisation
        boolean isEqual = false;

        // very close (including both equals 0.0) case
        if (equals(x, y)) {
            isEqual = true;
        }
        // common case
        else {
            // Relative difference computation
            final double absoluteMax = FastMath.max(FastMath.abs(x), FastMath.abs(y));
            final double relativeDifference = FastMath.abs((x - y) / absoluteMax);

            //test
            if (relativeDifference < eps) {
                isEqual = true;
            }
        }
        return isEqual;
    }


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