Re: Re: Two FindRoot questions

• To: mathgroup at smc.vnet.net
• Subject: [mg89888] Re: Re: [mg89872] Two FindRoot questions
• From: Bob Hanlon <hanlonr at cox.net>
• Date: Tue, 24 Jun 2008 03:21:16 -0400 (EDT)

```Or you could put the SetPrecision inside the function definition

Clear[f];

f[k_ /; k <= 0] :=
x /. FindRoot[x^2 + SetPrecision[k, 20], {x, 0, 10},
WorkingPrecision -> 20];

{f[-10], f[10]}

{3.1622776601683793320,f(10)}

Plot[f[k], {k, -10, 10}]

Bob Hanlon

---- Bob Hanlon <hanlonr at cox.net> wrote:
> Clear[f];
>
> f[k_ /; k <= 0] :=
>   x /. FindRoot[x^2 + k, {x, 0, 10}, WorkingPrecision -> 20];
>
> {f[-10], f[10]}
>
> {3.1622776601683793320,f(10)}
>
> Plot[f[SetPrecision[k, 20]], {k, -10, 10}]
>
>
> Bob Hanlon
>
> ---- Aaron Fude <aaronfude at gmail.com> wrote:
> > Hi,
> >
> > These are not FindRoot questions, per se...
> >
> > Here's a simple example which I want to ask three questions about:
> >
> > f[k_] := x /. FindRoot[x^2 + k, {x, 0, 10}];
> > f[-10]
> > Plot[f[k], {k, -10, 10}]
> >
> > First, I want the plot to only show where there exists a root.
> > Is the right solution to make f[] return Null?
> > How do I make f[] return Null? (Is there a way to "catch" the
> > warnings?)
> >
> > Finally, I need to solve my equations to 20 digits. How do I do that?
> > I've read about Accuracy and Precision but it didn't help.
> >
> > Thanks!
> >

```

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