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MathGroup Archive 2004

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Re: FindRoot cannot find obvious solution

  • To: mathgroup at smc.vnet.net
  • Subject: [mg47821] Re: FindRoot cannot find obvious solution
  • From: "Jens-Peer Kuska" <kuska at informatik.uni-leipzig-de>
  • Date: Wed, 28 Apr 2004 06:56:07 -0400 (EDT)
  • Organization: Uni Leipzig
  • References: <c6l872$ire$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

and what is with

h1 = 1 + (y - x)^2;
h2 = 1 + (2/3 - x^2)^2;
b = h2/(h1 + h2);
f = x(1 - x)^2;
s = f*D[b, y];

g[yy_?NumericQ] := NIntegrate[Evaluate[s /. y -> yy], {x, 0, 1}]

FindRoot[g[y] == 0, {y, 0.35, 0.45}]


Regards

 Jens



"Mukhtar Bekkali" <mbekkali at iastate.edu> schrieb im Newsbeitrag
news:c6l872$ire$1 at smc.vnet.net...
> Here is my code in Mathematica 5:
>
> h1=1+(y-x)^2;
> h2=1+(2/3-x^2)^2;
> b=h2/(h1+h2);
> f=x(1-x)^2;
> s=f*D[b,y];
> g[y_]:=NIntegrate[s,{x,0,1}];
> FindRoot[g[y]==0,{y,0.35,0.45}]
>
> The output is
>
> NIntegrate::inum: Integrand H is not numerical at {x} = {0.5`}.
> FindRoot::cvmit: Failed to converge to the requested accuracy or precision
> within 100 iteration
>
> and it gives me y->0.45 or the upper boundary. However, when I plot g[y] I
> can see that the solution is somewhere around y=0.4.  Using Solve instead
of
> FindRoot does not give me any solutions.
>
> What am I doing wrong here? Thank you in advance. Mukhtar Bekkali
>
>



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