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MathGroup Archive 2006

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Re: FindRoot & NDSolve

  • To: mathgroup at smc.vnet.net
  • Subject: [mg64670] Re: [mg64650] FindRoot & NDSolve
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Sun, 26 Feb 2006 05:07:52 -0500 (EST)
  • Reply-to: hanlonr at cox.net
  • Sender: owner-wri-mathgroup at wolfram.com

You can use Hold to keep NDSolve from trying to evaluate too soon.

FindRoot[Hold[(f/.NDSolve[{
    f'[x]-2 x-a==0,f[0]==0},f,{x,-3,3}][[1]])[2]==4],{a,-10,10}]


{a -> -7.3171562090692666*^-9}

However, the differential equation can be solved exactly

FindRoot[(f/.DSolve[{f'[x]-2 x-a==0,f[0]==0},f,x][[1]])[2]==4,{a,-10}]

{a -> 0.}

And so can the resulting equation

Solve[(f/.DSolve[{f'[x]-2 x-a==0,f[0]==0},f,x][[1]])[2]==4,a][[1]]

{a -> 0}


Bob Hanlon

> 
> From: Takashi Inoue <takash-i at sophia.ac.jp>
To: mathgroup at smc.vnet.net
> Subject: [mg64670] [mg64650] FindRoot & NDSolve
> 
> Hi all,
> 
> This is my first post to here.
> I have a problem and want your help.
> 
> Mathematica 4 did the following calculation with no pleblem,
> while Mathematica 5(.2)  cannot do it.
> 
> FindRoot[
>  (f /.NDSolve[ {D[f[x], {x,1}] - 2 x - a == 0, f[0] == 0}, f, {x, -3, 3} 
> ][[1]])[2] == 4,
>  {a, -10, 10}
>               ]
> 
> Does anyone know solution or altanative way to do it?
> 
> Takashi Inoue,
> Dept. Phys. Sophia University
> 
> 


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