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MathGroup Archive 2003

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Re: Emergent Help: NSolve Problems!

  • To: mathgroup at smc.vnet.net
  • Subject: [mg39790] Re: [mg39753] Emergent Help: NSolve Problems!
  • From: Dr Bob <drbob at bigfoot.com>
  • Date: Fri, 7 Mar 2003 03:38:51 -0500 (EST)
  • References: <200303060735.CAA09182@smc.vnet.net>
  • Reply-to: drbob at bigfoot.com
  • Sender: owner-wri-mathgroup at wolfram.com

It's a precision problem.  The first solution isn't -8.99998:

temp[s_] = s^10 + 10 s^9 + 10 s^8 + 10 s^7 + 10 s^6 + 10 s^5 + 10 s^4 + 1;
NSolve[temp[s] == 0, s]
NumberForm[First@%, 20]
temp[s] /. %
temp[-8.99998]
temp[-8.99998118013165]

Bobby

On Thu, 6 Mar 2003 02:35:04 -0500 (EST), Chengzhou Wang <wcz at ece.ucsd.edu> 
wrote:

> Hi, guys
>
> I have some complicated polynomials, and I want to calculate its roots.
> HOwever, when I use NSolve, it creates some problems. Say a simple
> example:
>
> temp[s_]=s^10+10 s^9+ 10 s^8 +10 s^7 +10 s^6+ 10 s^5 +10 s^4 +1; 
> NSolve[temp[s]==0, s]
>
> It will give:
>
> Out[4]= {{s -> -8.99998}, {s -> -1.06539}, {s -> -0.468828 - 0.886239 I},
>
>> {s -> -0.468828 + 0.886239 I}, {s -> -0.409684 - 0.469948 I},
>
>> {s -> -0.409684 + 0.469948 I}, {s -> 0.401048 - 0.312597 I},
>
>> {s -> 0.401048 + 0.312597 I}, {s -> 0.51015 - 0.878693 I},
>
>> {s -> 0.51015 + 0.878693 I}}
>
> But when I plug in the first number, which is "-8.99998", it should give 
> a
> value close to zero. However, it gives:
>
> In[5]:= temp[-8.99998]
> Out[5]= -411.473
>
> The other roots seems OK. Does anyone know why? This is just a simple
> example. I have some more complicated polynomials to deal with.
>
> Thanks in advance!
>
> PS: Please reply (cc) to my email. I did not subscribe my email to the
> this email group!
>
> --
> Chengzhou
>
>
>



-- 
majort at cox-internet.com
Bobby R. Treat



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