Version problem with FindRoot
- To: mathgroup at smc.vnet.net
- Subject: [mg97161] Version problem with FindRoot
- From: "Dr. Robert Kragler" <kragler at hs-weingarten.de>
- Date: Fri, 6 Mar 2009 05:39:09 -0500 (EST)
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