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
>
> 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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