[ruby-dev:28544] Re: Rational

>def rationalize(x, e = Float::EPSILON)
>  if x < 0
>    -rationalize(-x, e)
>  else
>    rational_within(x - e, x + e)
>  end
>end
>
>def rational_within(x, y)
>  xq, yq = x.floor, y.floor
>  if xq == x || x == y
>    Rational(xq)
>  elsif xq < yq
>    Rational(xq + 1)
>  else
>    xq + 1/rational_within(1/(y - yq), 1/(x - xq))
>  end
>end

これでは Rational(Math::PI) が 3 になってしまいました。

def rational_within(x, y)
  xq, yq = x.floor, y.floor
  if x == y
    Rational(x)
  elsif xq == x
    Rational(xq)
  elsif xq < yq
    Rational(xq + 1)
  else
    xq + 1/rational_within(1/(y - yq), 1/(x - xq))
  end
end

としないとまずいかな。