       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==x

> ,v==0,f==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

>

>

>

```

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