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MathGroup Archive 2006

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Re: Mathematica bugs?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg67316] Re: Mathematica bugs?
  • From: "David W.Cantrell" <DWCantrell at sigmaxi.org>
  • Date: Sun, 18 Jun 2006 05:13:02 -0400 (EDT)
  • References: <e70f29$rf4$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

"Yaroslav Bulatov" <yaroslavvb at gmail.com> wrote:
> When I run the following line
> x = Pi/4; For[i = 0, i < 56, i += 1, x = 2*Abs[x - 1/2]]; N[x]
> I get 3.
>
> But x should always stay between 0 and 1, why do I get 3?
>
> Also
> x = Pi/4; For[i = 0, i < 50, i += 1, x = 2*Abs[x - 1/2]]; N[Log[x]]
> gives me Indeterminate
>
> How can I get an indeterminate here?

Just ask for more precision from N:

In[107]:=
x = Pi/4; For[i = 0, i < 56, i += 1, x = 2*Abs[x - 1/2]]; N[x,20]

Out[107]=
0.79387245267980382900

In[108]:=
x = Pi/4; For[i = 0, i < 50, i += 1, x = 2*Abs[x - 1/2]]; N[Log[x],20]

Out[108]=
-3.3676443458316025909

David Cantrell


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