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Re: precisions

  • To: mathgroup at
  • Subject: [mg56011] Re: precisions
  • From: "Steve Luttrell" <steve_usenet at>
  • Date: Wed, 13 Apr 2005 01:10:54 -0400 (EDT)
  • References: <d3g92l$t1u$>
  • Sender: owner-wri-mathgroup at

Eigenvalues knows about Precision.

For instance, compare the following:

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



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


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> wrote in message 
news:d3g92l$t1u$1 at
> 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 (or) tma at

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