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MathGroup Archive 2006

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using FindRoot to find multiple answers in a domain?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg69059] using FindRoot to find multiple answers in a domain?
  • From: "akil" <akomur at wanadoo.nl>
  • Date: Tue, 29 Aug 2006 03:25:42 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

I want to find all answers that exist in a certain domain, but FindRoot 
gives only the first answer it finds (Using other methods like Solve,Reduce 
etc takes too long, so Im stuck with using FindRoot). I give the problem I 
have by example, the functions I use are really complex, but by solving the 
problem for the example, I could solve t for the complex part.

Example:

Finding all intersections of Cos[x] and Sin[x] in the domain [0,10Pi]

Doing:
FindRoot[Cos[antwoord] == Sin[antwoord], {antwoord, 0, 0, 10Pi}]

FindRoot[Cos[antwoord] == Sin[antwoord], {antwoord, %, %, 10Pi}]

does not work the second FindRoot gives the exact same answer back. So using 
this in a loop to find all intersections does not work.

Doing FindRoot[Cos[antwoord] == Sin[antwoord], {antwoord, %+0.01, %+0.01, 
10Pi}] instead, also does not work.

Any way to find all intersections in a specified domain?

Akil



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