bug?

[Ralf Hemmecke]

Maybe I don´t understand that code, but shouldn't

even?(denom(n))

actually be

denom(n) > 1

? There is no need for abs(denom(n)) here, since seemingly FRAC(INT)
never returns a negative denominator.

https://github.com/fricas/fricas/blob/master/src/algebra/interval.spad#L493

-- From RadicalCategory
_^(u : %, n : Fraction Integer) : % ==
lo : R := inf(u)
hi : R := sup(u)
lo <= 0 =>
even?(denom(n)) => -- <========= ???
error "fractional power only defined for x > 0"
even?(numer(n)) =>
hi < 0 =>
interval(0, lo^n)
interval(0, max(lo^n, hi^n))
interval(lo^n, hi^n)
interval(lo^n, hi^n)


Ralf

[Waldek Hebisch]

On Fri, Apr 04, 2025 at 11:50:47PM +0200, 'Ralf Hemmecke' via FriCAS - computer algebra system wrote:
> Maybe I don´t understand that code, but shouldn't
>
> even?(denom(n))
>
> actually be
>
> denom(n) > 1

No, compare with power in Float.

> https://github.com/fricas/fricas/blob/master/src/algebra/interval.spad#L493
>
> -- From RadicalCategory
> _^(u : %, n : Fraction Integer) : % ==
> lo : R := inf(u)
> hi : R := sup(u)
> lo <= 0 =>
> even?(denom(n)) => -- <========= ???
> error "fractional power only defined for x > 0"
> even?(numer(n)) =>
> hi < 0 =>
> interval(0, lo^n)
> interval(0, max(lo^n, hi^n))
> interval(lo^n, hi^n)
> interval(lo^n, hi^n)
>
>
> Ralf
>

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--
Waldek Hebisch