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From Luc Maisonobe <Luc.Maison...@free.fr>
Subject Re: [math] "equals" in "Vector3D"
Date Tue, 28 Apr 2009 18:41:24 GMT
Ted Dunning a écrit :
> This is a generally useful thing to have, but there are multiple definitions
> for how you apply the tolerance.  You should file a JIRA and add a patch!
> 
> Among the definitions that are commonly used, you will find:
> 
> L1 norm: equals(a, b, tolerance) = sum(abs(a-b)) < tolerance
> L2 norm: equals(a, b, tolerance) = sqrt(sum((a-b)^2)) < tolerance
> L-infinity norm: equals(a, b, tolerance) = max(abs(a-b)) < tolerance
> 
> All are useful.

I'll guess for 3D vector the L2-norm is the more useful as it is
invariant when physical orthonormal frames are changed.
I'll check in the variant you prefer.

Luc

> 
> Which did you think you wanted?
> 
> On Tue, Apr 28, 2009 at 6:23 AM, Gilles Sadowski <
> gilles@harfang.homelinux.org> wrote:
> 
>> Could we have a
>>
>>  boolean equals(Vector3D other,
>>                double tolerance)
>>
>> method?
>> Or even
>>
>>  static boolean equals(Vector3D v1,
>>                        Vector3D v2,
>>                        double tolerance)
>>
>> that would return true if the components are equal within the given
>> tolerance.
>>
>>
>> Best,
>> Gilles
>>
>> P.S. It seems that checking for exact equality (as the "equal(Object)"
>>     method does) is not very useful: If the two vectors being compared
>>     come from different computations, they will (most of the time) be
>>     different although, at the precision-level, they should be considered
>>     equal.
>>
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> 
> 


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