Re: Integrating Interpolating function

```> To integrate over an InterpolatingFunction, you need to use NIntegrate

You don't necessarily need to use NIntegrate.  Integrate will
automatically use numerical schemes on InterpolatingFunctions.  But you
have to apply the rule sol.  For example:

sol = NDSolve[{f'[t] == f[t], f[0] == 1}, f, {t, 0, 10}][[1]]

Integrate[f[t] /. sol, {t, 0, 5}]
NIntegrate[f[t] /. sol, {t, 0, 5}]

Best,
Robert

On Aug 3, 2011, at 6:39 AM, James Womack wrote:

>
> To integrate over an InterpolatingFunction, you need to use NIntegrate
> (numerical integration), rather than Integrate. Hope this helps!
>
> On 3 August 2011 12:07, math_new <dom.woe at gmail.com> wrote:
>
>> Hi,
>>
>> I solve a system of differential equations using NDSolve up to time
>> t_end. which gives me something like
>>
>> sol = {f->InterpolatingFunction}
>>
>> Now I want to do an integral like that
>>
>> Integrate[t*f[t],{t,0,tend}]
>>
>> but it won't be computed. What am I doing wrong?
>>
>> Cheers
>>
>>

```

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