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MathGroup Archive 2005

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Re: precisions

  • To: mathgroup at smc.vnet.net
  • Subject: [mg56011] Re: precisions
  • From: "Steve Luttrell" <steve_usenet at _removemefirst_luttrell.org.uk>
  • Date: Wed, 13 Apr 2005 01:10:54 -0400 (EDT)
  • References: <d3g92l$t1u$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Eigenvalues knows about Precision.

For instance, compare the following:

Eigenvalues[{{1., 2.}, {3., 4.}}]

{5.37228,-0.372281}

and

Eigenvalues[{{1.`30., 2.`30.}, {3.`30., 4.`30.}}]

{5.37228132326901432992530573411,-0.372281323269014329925305734109}

My guess is that you evaluated SetPrecision[inputdata,100] and discarded the 
result. SetPrecision[x,n] does NOT change x itself. However, 
y=SetPrecision[x,n] creates y which is a version of x with Precision equal 
to n.

Steve Luttrell

"Tun Myint Aung" <TMA at nus.edu.sg> wrote in message 
news:d3g92l$t1u$1 at smc.vnet.net...
>
> Hi All,
>
>    I am doing a calculation involving eigenvalues and eigenvectors for
> structural mechanics. I encountered with difficulties in numerical
> calculation which is very sensitive to precisions of numerical numbers.
> I used "SetPrecision[inputdata,100] for my input data. But after I got
> eigenvalues and eigenvectors, these numbers are "MachinePrecision". I
> tried to change the precision in "Eigenvalues", but there are no options
> for that. How can I set the precision for the whole notebook?
>
>
> With Regards,
> Tun Myint Aung (Graduate Student)
> Civil Engineering Department
> National University of Singapore
> E1A 02-18
> E-mail: g0202015 at nus.edu.sg (or) tma at nus.edu.sg
>
>
>
>
>
> 



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