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Re: Find roots in a limited interval

  • To: mathgroup at smc.vnet.net
  • Subject: [mg86739] Re: Find roots in a limited interval
  • From: Szabolcs Horvát <szhorvat at gmail.com>
  • Date: Thu, 20 Mar 2008 02:51:30 -0500 (EST)
  • Organization: University of Bergen
  • References: <frqpvr$5be$1@smc.vnet.net>

viktor.albers at gmail.com wrote:
> Dear all,
> 
> Being a Mathematica beginner I struggle to find a solution to a fairly
> simple problem. I have a function (superposition of several weighted
> sinc functions) which in principle has infinitely many roots.
> 
> However I am interested only in lets say roots that are to be found
> within the limited interval between 0 and 5.
> 
> I tried to define a system of inequalities of the type
> 
> Solve[f[t] && t>0 && t<5, t] but no success.

--------^^^
This doesn't make sense unless f[t] is a logical statement.  && means 
"and", so this is like saying "4 and 3 < 5".  Perhaps you meant

Reduce[f[t] == 0 && t > 0 && t < 5, t, Reals]

?  If this doesn't work, then most probably Mathematica cannot solve the 
equation symbolically, and you need to resort to numerical methods.

FindRoot[f[t] == 0, {t, 1, 0, 5}]

will give you a single solution between 0 and 5.  Tweak the starting 
value 1 to get different solutions.

> I played around with the function Reduce but did not have any success
> and I am also not sure if this is the right way forward.

Yes, Reduce is the command for solving inequalities or equations with 
conditions, but next time please show the exact command you used, 
otherwise it is impossible to guess what went wrong.

> 
> So the question: Is it possible to define an interval in Mathematica
> in which I am looking for the roots?
> 
> Thank you for your time.
> 
> Regards,
> Viktor
> 
> 


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