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MathGroup Archive 2007

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Re: Re: Weird result in Mathematica 6

  • To: mathgroup at smc.vnet.net
  • Subject: [mg76477] Re: [mg76431] Re: [mg76393] Weird result in Mathematica 6
  • From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
  • Date: Wed, 23 May 2007 05:09:39 -0400 (EDT)
  • References: <26727995.1179743868970.JavaMail.root@m35> <200705220647.CAA19795@smc.vnet.net>

I don't see any connection between these two issues. Moreover, I get:

FindRoot[h == g, {x, 0}]
FindRoot::njnum:The Jacobian is not a matrix of numbers at {x} = 
{0.}. >>
{x -> 0.}

which explains what is wrong (error messages can tell you a lot, 
sometimes).  Trying a slightly different starting search point:

FindRoot[h == g, {x, 0.1}]
{x->2.}

  {g, h} /. %
  {0., 0.}


Andrzej Kozlowski


On 22 May 2007, at 15:47, DrMajorBob wrote:

> Even worse, FindRoot returns a wrong answer:
>
> g = Piecewise[{{0, x < 0}, {2 x - x^2, 0 <= x < 4}, {16 x - x^2,
>      x=B34}}];
> 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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