Re: Integrating Interpolating function

• To: mathgroup at smc.vnet.net
• Subject: [mg120701] Re: Integrating Interpolating function
• From: DrMajorBob <btreat1 at austin.rr.com>
• Date: Thu, 4 Aug 2011 02:53:16 -0400 (EDT)
• Delivered-to: l-mathgroup@mail-archive0.wolfram.com
• References: <201108031107.HAA10850@smc.vnet.net>

```> s = NDSolve[{y'[x] == y[x] Cos[x + y[x]], y[0] == 1}, y, {x, 0, 30}]
> NIntegrate[t*s[t], {t, 0, 30}]
>
> does what you are looking for.

No, it doesn't. Instead, you need something like

s = y /. First@
NDSolve[{y'[x] == y[x] Cos[x + y[x]], y[0] == 1}, y, {x, 0, 30}];
NIntegrate[t*s[t], {t, 0, 30}]

46.9655

Bobby

On Wed, 03 Aug 2011 18:20:37 -0500, Oliver Ruebenkoenig
<ruebenko at wolfram.com> wrote:

> On Wed, 3 Aug 2011, math_new 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
>>
>>
>
> Hi
>
> s = NDSolve[{y'[x] == y[x] Cos[x + y[x]], y[0] == 1}, y, {x, 0, 30}]
> NIntegrate[t*s[t], {t, 0, 30}]
>
> does what you are looking for.
>
> Hth,
> Oliver
>

--
DrMajorBob at yahoo.com

```

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