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MathGroup Archive 2005

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Re: RootSearch-missing root

  • To: mathgroup at smc.vnet.net
  • Subject: [mg62252] Re: RootSearch-missing root
  • From: dh <dh at metrohm.ch>
  • Date: Thu, 17 Nov 2005 17:03:47 -0500 (EST)
  • References: <dlen7g$8d1$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi Ania,
RootSearch is not a Mathematica function (at least not in version 5.0).

Further, with question like this you should give a sample input.

However, there is a package RootSearch from the author:
  ted.ersek at navy.navy.mil

This package is numerical! No numerical routine can garantee (for a 
general function)that it can find all the roots. Every numerical routine 
must sample some interval and can miss. To see this, simply consider a 
function of a real argument that is positive everywhere and dips below 
zero only on a very short interval.
The best you can do is to increase the number of sample points.

sincerely, Daniel

nastazjaf wrote:
> Hello,
> 	I have a problem with the RootSearch. I have searched the archive and 
> the RootSearch Examples and couldn't find an answer or at least the 
> similar problem. The RootSearch doesn't find one of the roots. There are 
> three roots, all three are clearly resolved when two functions are 
> plotted but RootSearch finds only two of them. I tried to play with the 
> options and with different values of xmax and xmin, and it just doesn't 
> see it. FindRoot finds the missing root for well defined starting 
> values. But I need to have all three roots. In what circumstances the 
> RootSearch cannot find one of the roots?
> 
> Thanks
> Ania
> 


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