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FindRoot problem
Posted:
Sep 20, 1996 12:43 AM


Dear All,
I came to the conclusion that FindRoot sometimes behaves a bit strange. Say I want to calculate: x=x/.First[FindRoot[(xPi),{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[xRationalize[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
Email: acus@itpa.lt Fax: 3702225361 Tel: 3702612906



