Re: Default Precision isn't reached yet no warning about convergence are generated

*To*: mathgroup at smc.vnet.net*Subject*: [mg44658] Re: [mg44653] Default Precision isn't reached yet no warning about convergence are generated*From*: Andrzej Kozlowski <akoz at mimuw.edu.pl>*Date*: Thu, 20 Nov 2003 03:16:24 -0500 (EST)*References*: <200311190959.EAA22301@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

On 19 Nov 2003, at 18:59, Michael Beqq wrote: > I have some doubts about solutions found by FindRoot. I solved some > equation f[x]=0 and found some x*. Now, if I plug x* back into f[x] > then I > should get zero or something close to zero based on MaxPrecision, > which is, > I believe, is equal to 10^-50. However, I get f[x*]=10^-9 which is a > lot > less than 10^-50 yet while solving FindRoot does not give me any > warnings > about failure to coverge. This is true for both Newton and Secant > method. > I increased precision to 200, MaxPrecision->200, but the results are > the > same. Shall I accept solutions found by Mathematica as true > solutions? I > have version 4.0. Thanks. > > > You should increase WorkingPrecision, not just MaxPrecision. Also, check the precision of your input. It should be at least as precise as your WorkingPrecision. In particular, if you are using machine precision number in your input all this won't do you any good. You should really send your example otherwise it is hard to tell what you are really doing. Andrzej Kozlowski Chiba, Japan http://www.mimuw.edu.pl/~akoz/

**References**:**Default Precision isn't reached yet no warning about convergence are generated***From:*"Michael Beqq" <mbekkali@iastate.edu>