Re: Absolute value of intervals

From: Jasen Betts <jasen(at)xnet(dot)co(dot)nz>
To: pgsql-general(at)postgresql(dot)org
Subject: Re: Absolute value of intervals
Date: 2009-11-02 11:22:00
Message-ID: hcmfco$55l$
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On 2009-10-27, Sam Mason <sam(at)samason(dot)me(dot)uk> wrote:
> On Tue, Oct 27, 2009 at 03:25:02PM +0000, Sam Mason wrote:
>> If the absolute value of an interval was defined to strip out all the
>> negation signs you'd get the "wrong" answers out.
> Oops, forgot another reason! For maths to work (n) and (-(-n)) should
> evaluate to the same value. Inverting all the signs, as negation does,
> will ensure that these semantics remain.

There not requrement in mathematics that

z be a member of the set { abs(z) , -abs(z) }

consider the case of z=sqrt(-1)

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