Re: plotting even function

[Geraint Paul Bevan]

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Henry F. Mollet wrote:
> x1 = 0.50000
> octave:23> x1^(1/3)
> ans = 0.79370
> octave:24> x2=-0.5
> x2 = -0.50000
> octave:25> x2^(1/3)
> ans = 0.39685 + 0.68736i
> octave:26> abs(ans)
> ans = 0.79370
> Will the above work?
> Henry
>

It finds the correct magnitude but the sign is wrong for negative x so
it must be multiplied by sign(x).

octave> function y = cbrt (x)
> y = sign(x) .* (abs(x).^(1/3));
> endfunction

octave> cbrt([-8,-64,8])
ans =

  -2.0000  -4.0000   2.0000

- --
Geraint Bevan
http://homepage.ntlworld.com/geraint.bevan

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