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Re: Using NDSolve and Finding a specific Value

  • To: mathgroup at smc.vnet.net
  • Subject: [mg85375] Re: Using NDSolve and Finding a specific Value
  • From: "Kevin J. McCann" <Kevin.McCann at umbc.edu>
  • Date: Thu, 7 Feb 2008 22:28:51 -0500 (EST)
  • Organization: University System of Maryland
  • References: <foek87$i3s$1@smc.vnet.net>

I am sure that you will get a lot of responses, but here is mine:

try:

eye[t_] = i[t] /. sols[[1]]

Then

eye[3.8]
0.324902


Kevin

Note the [[1]]. The InterpolationFunction answer is in double wigglies: 
{{....}}. The [[1]] pulls it out so there is no enclosing {}.


Tara.Ann.Lorenz at gmail.com wrote:
> Hello.
> 
> I am having an issue related to the NDSolve function (I am using
> Version 6).  The following example illustrates the problem I am
> having:
> 
> Input:
> sols = NDSolve[{i'[t] == (1/8.516011) (-i[t] + 0.596120754),
>    i[1] == 0.219319}, i[t], {t, 1, 4}]
> 
> Output:
> {{i[t]->InterpolatingFunction[{{1.,4.}},<>][t]}}
> 
> I then would like to solve i[t] for t=3.8
> According to the Mathematica website, I should be able to enter the
> following input to receive my answer:
> 
> i[3.8]/.sols
> 
> However, my output is simply i[3.8] and not a numerical value.  What
> else can I try to get a numerical value from the interpolating
> function.
> 
> I appreciate any feedback. Thank you
> 
> 
> 

-- 

Kevin J. McCann
Research Associate Professor
JCET/Physics
Physics Building
University of Maryland, Baltimore County
1000 Hilltop Circle
Baltimore, MD 21250


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