Re: Version problem with FindRoot
- To: mathgroup at smc.vnet.net
- Subject: [mg97285] Re: Version problem with FindRoot
- From: dh <dh at metrohm.com>
- Date: Tue, 10 Mar 2009 05:33:37 -0500 (EST)
- References: <goqug8$ng0$1@smc.vnet.net>
Hi Robert,
FindRoot first calls gun[x] with a symbolic argument to check if it can
make simplifications. To prevent evaluation of gun with a symbolic
argument, declare it so that is evaluated only for numeric arguments:
gun[x_?NumericQ] := (soln =
NDSolve[system[x], {w, v, f}, {n, 0, 10}])[[1, 2, 2]][10.]
hope this helps, Daniel
Dr. Robert Kragler wrote:
> Hi,
>
> according to a short note of Alan Hayes, TJM Vol.3, issue 3 (1993 ! )
> there is a 3-liner given for solving boundary problems of ODEs with the
> help of the so-called shooting method. The subsequent program
>
> system[x_]={2 w'[n]+f[n]* w[n]==0,w[n]==v'[n],v[n]==f'[n],w[0]==x
> ,v[0]==0,f[0]==0 }
>
> gun:=(soln=NDSolve[system[#],{w,v,f},{n,0,10}])[[1,2,2]][10.]&
>
> FindRoot[gun[x]==1,{x,1,.5}] (* should give x->0.332058 *)
>
> works with earlier Mathematica versions 3.0, 4.2 but NOT for 5.2 (which
> I am currently still using in order to finish a manuscript before I will
> adapt this to version 7.0). In Mathematica version 6.0 and 7.0 FindRoot
> will work again if the following (version 6 ) system option is used :
>
> SetSystemOptions["EvaluateNumericalFunctionArgument"->False]
>
> There is no problem to plot the function gun[x]with Plot[gun[x],{x,0,1}]
> in Mathematica.
> However, in Mathematica version 5.2 FindRoot gives rise to the following
> (error) message :
>
> NDSolve::"ndinnt": "Initial condition x is not a number or a rectangular
> array of numbers."
>
> FindRoot::nlnum : The function value {-1.+v´[n][10.`] is not a list of
> numbers with
> dimensions {1} at {x} = {1.`}.}
>
> Does anybody have an idea what to do in the case of version 5.2 ? Thanks
> for any suggestion.
>
> Robert Kragler
>
> email: kragler at hs-weingarten.de
>
>
>