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MathGroup Archive 2007

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Re: Weird result in Mathematica 6

  • To: mathgroup at smc.vnet.net
  • Subject: [mg76431] Re: [mg76393] Weird result in Mathematica 6
  • From: DrMajorBob <drmajorbob at bigfoot.com>
  • Date: Tue, 22 May 2007 02:47:39 -0400 (EDT)
  • References: <26727995.1179743868970.JavaMail.root@m35>
  • Reply-to: drmajorbob at bigfoot.com

Even worse, FindRoot returns a wrong answer:

g = Piecewise[{{0, x < 0}, {2 x - x^2, 0 <= x < 4}, {16 x - x^2,
     x³4}}];
h = x - 2;
FindRoot[h == g, {x, 0}]
{g, h} /. %

{x->-2.84217*10^-15}
{0, -2.}

Bobby

On Mon, 21 May 2007 05:01:21 -0500, Sebastian Meznaric  
<meznaric at gmail.com> wrote:

> I was playing around with Mathematica 6 a bit and ran this command to
> solve for the inverse of the Moebius transformation
>
> FullSimplify[
>  Reduce[(z - a)/(1 - a\[Conjugate] z) == w && a a\[Conjugate] < 1 &&
>    w w\[Conjugate] < 1, z]]
>
> This is what I got as a result:
> -1 < w < 1 && -1 < a < 1 && z == (a + w)/(1 + w Conjugate[a])
>
> Why is Mathematica assuming a and w are real? The Moebius
> transformation is invertible in the unit disc regardless of whether a
> and w are real or not. Any thoughts?
>
>
>



-- 
DrMajorBob at bigfoot.com


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