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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: [mg76558] Re: [mg76431] Re: [mg76393] Weird result in Mathematica 6
  • From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
  • Date: Thu, 24 May 2007 05:54:55 -0400 (EDT)
  • References: <26727995.1179743868970.JavaMail.root@m35> <200705220647.CAA19795@smc.vnet.net> <9745176.1179921476358.JavaMail.root@m35> <op.tssgfzliqu6oor@monster.ma.dl.cox.net>

Yes, its curious. It might just be "platform dependence" but is more 
likely to be  "time of release dependence". Mine is:


$Version

"6.0 for Mac OS X PowerPC (32-bit) (April 20, 2007)"

Andrzej


On 24 May 2007, at 01:37, DrMajorBob wrote:

> Interesting. But your results are entirely different from mine, for =

> the same input.
>
>> which explains what is wrong (error messages can tell you a lot, 
>> sometimes).
>
> And frequently, they don't.
>
> Here's the error message at THIS machine:
>
> FindRoot::lstol: The line search decreased the step size to within \
> tolerance specified by AccuracyGoal and PrecisionGoal but was unable \
> to find a sufficient decrease in the merit function.  You may need \
> more than MachinePrecision digits of working precision to meet these \
> tolerances. >>
>
> Bobby
>
> On Tue, 22 May 2007 06:28:08 -0500, Andrzej Kozlowski 
> <akoz at mimuw.edu.pl> wrote:
>
>> *This message was transferred with a trial version of CommuniGate
>> (tm) Pro*
>> 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
>>>
>>
>>
>
>
>
> --
> DrMajorBob at bigfoot.com



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