[Octave-bug-tracker] [bug #42589] Inaccurate results with the colon operator

[Julien Bect]

URL:
  <http://savannah.gnu.org/bugs/?42589>

                 Summary: Inaccurate results with the colon operator
                 Project: GNU Octave
            Submitted by: jbect
            Submitted on: jeu. 19 juin 2014 17:01:06 GMT
                Category: None
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Inaccurate Result
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: dev
        Operating System: GNU/Linux

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Details:

I get this result with Octave 3.6.4 and 3.9.0+ (both built with gcc 4.7.3 on
Ubuntu 13.04 i686-linux-gnu):


>> x = -1:.1:1;  x(11)
ans = 5.55111512312578e-17


Matlab (2012a) returns exactly 0.

Trying to understand the cause of this error, I proceeded with some additional
experiments which give rather surprising results:


>> x = -1 + ((0:10) * .1);  x(11)
ans = 5.55111512312578e-17
>> x = -1 + ((9:10) * .1);  x(2)
ans = 2.77555756156289e-17
>> x = -1 + (10 * .1)
x =                    0


Again, Matlab returns exactly 0 in all three cases.

Could somebody please confirm these results before I start to investigate ?





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