Re: Two FindRoot questions
- To: mathgroup at smc.vnet.net
- Subject: [mg89887] Re: [mg89872] Two FindRoot questions
- From: Bob Hanlon <hanlonr at cox.net>
- Date: Tue, 24 Jun 2008 03:21:05 -0400 (EDT)
- Reply-to: hanlonr at cox.net
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!
>