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Topic: FindRoot problem
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Arturas Acus

Posts: 53
Registered: 12/7/04
FindRoot problem
Posted: Sep 20, 1996 12:43 AM
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Dear All,

I came to the conclusion that FindRoot sometimes behaves a bit
strange. Say I want to calculate:
x=x/.First[FindRoot[(x-Pi),{x,-4,4},AccuracyGoal->20, WorkingPrecision->30,
Compiled->False,MaxIterations->Infinity]

The result of this is MachineNumber!!! It seems, problem is related
with evaluation of Pi. And hint N[Pi,30] do not help!!

Then I tried:

x=x/.First[FindRoot[x-Rationalize[N[Pi,30],0],{x,{-4,4}},
Compiled->False,AccuracyGoal->20,MaxIterations->Infinity,
WorkingPrecision->30]]

3.141592653589793238462643383279

Now it works correct. Does anybody had similar problem?
I tried two methods: secant and brent's. Both gives the same
results. Can anybody explain this behaviour? This is important for my
job.
Sincerely
Arturas Acus



Arturas Acus
Institute of Theoretical
Physics and Astronomy
Gostauto 12, 2600,Vilnius
Lithuania


E-mail: acus@itpa.lt
Fax: 370-2-225361
Tel: 370-2-612906







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