       Re: precisions

• To: mathgroup at smc.vnet.net
• Subject: [mg56003] Re: precisions
• From: Peter Pein <petsie at arcor.de>
• Date: Wed, 13 Apr 2005 01:10:40 -0400 (EDT)
• References: <d3g92l\$t1u\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Tun Myint Aung wrote:
> 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
>
>
>
>
>
>
Maybe you misunderstood the functionality of SetPrecision. This function
_returns_ the input set to the desired precision (as the help tells us:
"SetPrecision[expr, p] does not modify expr itself."):

ma=Table[Random[Integer,{-10,10}],{3},{3}];
Eigenvalues[SetPrecision[N[ma],100]]
Out=
{9.636466115429107974954053903389252568799915085039198891751834259486597151544\
511131541150948460400505...Rest of output left out}

--
Peter Pein
Berlin

```

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