Mailing-List: contact issues-help@commons.apache.org; run by ezmlm
Precedence: bulk
Reply-To: issues@commons.apache.org
Date: Mon, 19 Sep 2016 17:28:22 +0000 (UTC)
From: "Brian McCormick (JIRA)" <jira@apache.org>
To: issues@commons.apache.org
Message-ID: <JIRA.13005905.1474292850000.607308.1474306102034@Atlassian.JIRA>
In-Reply-To: <JIRA.13005905.1474292850000@Atlassian.JIRA>
References: <JIRA.13005905.1474292850000@Atlassian.JIRA> <JIRA.13005905.1474292850901@arcas>
Subject: [jira] [Commented] (MATH-1386) EPSILON value in
  org.apache.commons.math.util.MathUtils seems like half of what it should
 be
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit
archived-at: Mon, 19 Sep 2016 17:28:24 -0000


    [ https://issues.apache.org/jira/browse/MATH-1386?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15504074#comment-15504074 ] 

Brian McCormick commented on MATH-1386:
---------------------------------------

double epsilon = Double.longBitsToDouble(Double.doubleToLongBits(1) + 1) -
1;

Brian McCormick
MCB Systems Inc.
Phone: 918-749-5453
email: Brian.McCormick@mcbsystems.us


> 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
>   Original Estimate: 1h
>  Remaining Estimate: 1h
>
> 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. 


--
This message was sent by Atlassian JIRA
(v6.3.4#6332)