dolfin team mailing list archive

["Garth N. Wells" <gnw20@xxxxxxxxx>]

Here's an extensive discussion on comparing floats:

http://www.cygnus-software.com/papers/comparingfloats/comparingfloats.htm

Garth

On 08/07/11 11:44, Garth N. Wells wrote:
> 
> 
> On 08/07/11 11:33, Martin Sandve Alnæs wrote:
>> I already explained this, but let me make it clearer:
>>
>> If
>>   x >> eps,
>> such that
>>   x + eps == x,
>> then near(x, x) implemented as
>>   x < x + eps
>> will be equivalent to
>>   x < x
>> which is false.
>>
> 
> eps should be scaled.
> 
>> Clearly, near(x,x) should always be true in a correct implementation.
>> Using x <= x + eps fixes this. This is not "relying on equality",
>> that would be using ==.
>>
>> If you have a failing test case, show it to me and I will see what I can do.
>>
> 
> See buildbot.
> 
> Garth
> 
>> Martin
>>
>>
>> On 8 July 2011 12:21, Garth N. Wells <gnw20@xxxxxxxxx> wrote:
>>> I think that this is a 'bug' in the test. Relying on equality (i.e. <=
>>> versus <) for non-integers will lead to problems somewhere (like the
>>> 32-bit buildbot failing).
>>>
>>> Garth
>>>
>>>
>>> On 08/07/11 09:23, noreply@xxxxxxxxxxxxx wrote:
>>>> ------------------------------------------------------------
>>>> revno: 6054
>>>> committer: Martin Alnes <martinal@xxxxxxxxx>
>>>> branch nick: work
>>>> timestamp: Fri 2011-07-08 10:20:54 +0200
>>>> message:
>>>>   Re-introduce bugfix in near after recent mistaken(?) re-introduction of the bug, or something... Also disable debug print in test.
>>>> modified:
>>>>   dolfin/math/basic.cpp
>>>>   test/unit/math/python/basic.py
>>>>
>>>>
>>>> --
>>>> lp:dolfin
>>>> https://code.launchpad.net/~dolfin-core/dolfin/main
>>>>
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>>>
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> 
> 
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