[kepler-dev] Fwd: [Kepler - Bug #6439] (New) Double rounding fails in some cases while evaluating Expressions

[Edward Lee]

I doubt this is a new issue. The underlying arithmetic is IEEE 754.
Floating point numbers have the following problems (at least):

- addition is not associative
- not all decimal numbers within the range of representable numbers are 
representable exactly

Basically, it is rarely justifiable to test for equality of doubles.

Edward


On 3/4/14 11:21 AM, Matt Jones wrote:
> Daniel and Christopher --
>
> Do either of you have any insight into this new rounding issue?  Can 
> you confirm whether or not this is new behavior?
>
> Matt
>
> ---------- Forwarded message ----------
> From: <noreply at nceas.ucsb.edu <mailto:noreply at nceas.ucsb.edu>>
> Date: Tue, Mar 4, 2014 at 3:24 AM
> Subject: [Kepler - Bug #6439] (New) Double rounding fails in some 
> cases while evaluating Expressions
> To:
>
>
> Issue #6439 has been reported by Owsiak Michal.
> ------------------------------------------------------------------------
>
>
>   Bug #6439: Double rounding fails in some cases while evaluating
>   Expressions <https://projects.ecoinformatics.org/ecoinfo/issues/6439>
>
>   * Author: Owsiak Michal
>   * Status: New
>   * Priority: Urgent
>   * Assignee: Derik Barseghian
>   * Category: actors
>   * Target version: 2.3.0
>   * Bugzilla-Id:
>
> It seems that addition of doubles can produce values slightly 
> different than they should to be.
>
> Please take a look at attached workflow (simple_error.xml).
>
> Condition that should be satisfied to escape the loop is: 1.7 > 1.5 + 0.1
>
> However, loop is interrupted sooner, because of incorrect calculation 
> of doubles. Value of "p" is set to: 1.6000000000000003
>
> This, of course, makes it impossible to use doubles as check points 
> for the loops.
>
> However, it seems that casting to string and back works fine (take a 
> look at second workflow - simple.xml)
>
> Cheers
>
> Michal
>
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