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MathGroup Archive 1999

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Re: Why Doesn't N[Pi,i] Give i Digits For Small i, Mathematica

  • To: mathgroup at smc.vnet.net
  • Subject: [mg20234] Re: Why Doesn't N[Pi,i] Give i Digits For Small i, Mathematica
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Fri, 8 Oct 1999 18:30:13 -0400
  • Organization: Universitaet Leipzig
  • References: <7tgsdm$snl@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

N[] just create a double from its argument. Since double has 16 digits
it will be always work with this precision.

You need something like

TruncateReal[r_, i_Integer] := N[FromDigits[RealDigits[N[Pi, i], 10,
i]]]
  

Hope that helps
  Jens

R&M wrote:
> 
> If I execute:
> 
> Table[{i, N[Pi, i]}, {i, 1, 20}]
> 
> I get:
> 

SNIP SNAP

> I'd expect something like
> {{1,3},{2,3.1},{3,3.14},{4,3.141},{5,3.1416},{6,3.14159},{7,3.141593},....
> 
> It seems N[] only works as expected above 16 digits of requested
> precision.
> 
> Is my expectation wrong?  What should I do to get what I want?
> 
> My platform is WinNT 4 SP4.


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