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Re: integrate problem

  • To: mathgroup at smc.vnet.net
  • Subject: [mg98849] Re: integrate problem
  • From: Erik Max Francis <max at alcyone.com>
  • Date: Mon, 20 Apr 2009 19:07:27 -0400 (EDT)
  • References: <gshft4$c0o$1@smc.vnet.net>

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 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.

In your examples, is a constant, but s[t] is a function of t.  You 
haven't specified what that function is, so Mathematica can't simplify 
it beyond recognizing that you're asking for a symbolic integral. 
Specify what s[t] is either inline in the Integrate function or 
separately with a definition before trying to integrate 1/(s[t] + a).

-- 
Erik Max Francis && max at alcyone.com && http://www.alcyone.com/max/
  San Jose, CA, USA && 37 18 N 121 57 W && AIM, Y!M, Skype erikmaxfrancis
   Whom God has put asunder, why should man put together?
    -- Ralph Waldo Emerson


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