[jira] [Created] (MATH-1386) EPSILON value in org.apache.commons.math.util.MathUtils seems like half of what it should be

["Brian S. McCormick (JIRA)" <ji...@apache.org>]

Brian S. McCormick created MATH-1386:
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             Summary: EPSILON value in  org.apache.commons.math.util.MathUtils seems like half of what it should be
                 Key: MATH-1386
                 URL: https://issues.apache.org/jira/browse/MATH-1386
             Project: Commons Math
          Issue Type: Bug
         Environment: win 7
            Reporter: Brian S. McCormick


I've always used 1.1920929E-7 for dealing with float epsilon values. When dealing with double I've always used 2.220446049250313E-16 for epsilon.

You have it defined in org.apache.commons.math.util.MathUtils as 1.1102230246251565E-16 which is half what I think it should be.

I come up with these numbers using the following:

float fEps = Float.intBitsToFloat(Float.floatToIntBits(1f) + 1) - 1;
double dEps = Double.longBitsToDouble(Double.doubleToLongBits(1) + 1) - 1;

Am I correct? I don't really know. I do know that float epsilon in every legacy C/C++ compiler etc I have ever used is defined as about 1e-7 and this is the value using the formula for fEps above. When I started doing comps using doubles instead of floats I started using the formula for dEps above which looks to me like the equivalent for double numbers. 



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