On Mon, May 11, 2026 at 11:41:39AM +0800, Qian Yun wrote:
> lo <= 0 =>
> even?(denom(n)) =>
> error "fractional power only defined for x > 0"
> even?(numer(n)) =>
> hi < 0 =>
> interval(hi^n, lo^n) -- lo < hi <=0
> interval(0, max(lo^n, hi^n)) -- lo <=0 < hi
> interval(lo^n, hi^n) -- lo <=0, odd power
> interval(lo^n, hi^n) -- lo > 0
>
>
> I think there is no problem in other branch?
Right, I overlooked to 'lo <= 0' test above.
> Also, I just found out that Interval supports negative fractional
> power, but not negative integer power.
>
> AIntervalCategory does not support both.
>
> I guess that Interval did not want to deal with inverse of
> [a,b] where a<0<b?
Yes, we do not want this: this is moral equivalent of division
by 0.
--
Waldek Hebisch
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