I do find this behavior quite surprising--diameter should be an alias
for either relative or absolute diameter, not depending on the
interval.
On Wed, Oct 22, 2014 at 2:44 AM, John Cremona <john.crem...@gmail.com> wrote:
> I am trying to use the Real Interval Field (RIF), which in principle
> does exactly what I want. But I cannot understand this:
>
> sage: a=RIF(-1,1)
> sage: a.diameter()
> 2.00000000000000
> sage: [b.diameter() for b in a.bisection()]
> [1.00000000000000, 1.00000000000000]
> sage: [[c.diameter() for c in b.bisection()] for b in a.bisection()]
> [[0.666666666666667, 0.500000000000000],
> [0.500000000000000, 0.666666666666667]]
>
> I bisect an interval of length ("diameter") 2 twice, but 2 of the 4
> pieces have diameter 2/3! I assumed that the diameters of the output
> of bisection() added to the original diameter, but this appears not to
> be happening. If this is not a bug then I don't understand something.
>
> Perhaps this makes it clearer:
>
> sage: a=RIF(-1,1)
> sage: b=a.bisection()[0]
> sage: c=b.bisection()[0]
> sage: c.lower()
> -1.00000000000000
> sage: c.upper()
> -0.500000000000000
> sage: c.diameter()
> 0.666666666666667
>
> I think that what I need is
>
> sage: c.absolute_diameter()
> 0.500000000000000
>
> but did not understand "diameter". OK, so I have answered my own
> question, but I think I might as well post it anyway!
>
> John Cremona
>
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