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Re: integrate problem

  • To: mathgroup at smc.vnet.net
  • Subject: [mg98862] Re: integrate problem
  • From: Bill Rowe <readnews at sbcglobal.net>
  • Date: Mon, 20 Apr 2009 19:09:54 -0400 (EDT)

On 4/20/09 at 5:39 AM, sean_incali 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 I asked you to integrate an arbitrary function of time and
*did not* specify any details of the function could you do it?
Note, this is exactly what you are asking Mathematica to do.

>If the function that needs to be integrated w.r.t time is 1/(s[t] +
>a), how do I accomplish that?

define s[t] before asking Mathematica to do the integration

>It seems like if integrate it wrt to s [t] it will work.

>Integrate[1/(s[t] + a), s[t]]

This is no different than

Integrate[1/(s + a), s]

If you want a solution in terms of t, you first have to define
s[t]. There is no other way.




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