Re: integrate problem

• To: mathgroup at smc.vnet.net
• Subject: [mg98851] Re: integrate problem
• From: "Sjoerd C. de Vries" <sjoerd.c.devries at gmail.com>
• Date: Mon, 20 Apr 2009 19:07:49 -0400 (EDT)
• References: <gshft4\$c0o\$1@smc.vnet.net>

```Sean,

What you are really asking is: how can I integrate an unknown function
of t?

The short answer is: you can't.

If you are going to integrate something, the least prerequisite is
that you know what this something is.

Just try s[t] = t and s[t]=Sin[t] to see what an enormous difference
this makes for the answer. It is clear that a general answer in terms
of s[t] would not be very possible or useful.

Cheers -- Sjoerd

On Apr 20, 11:39 am, sean_inc... at yahoo.com wrote:
> I'm having some issues understanding this...  Following works as
> expected.
>
> s is the variable in time.  a is a parameter.
>
> Integrate[1/(s + a), s]
>
> gives Log[a + s]
>
> But the following gives the integral itself.
>
> Integrate[1/(s[t] + a), t]
>
> If the function that needs to be integrated w.r.t time is 1/(s[t] +
> a), how do I accomplish that?  It seems like if integrate it wrt to s
> [t] it will work.
>
> Integrate[1/(s[t] + a), s[t]]
>
> But does that sound about right?
>
> Any thoughts appreciated.
>
> Sean

```

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