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MathGroup Archive 2006

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Re: Limit Question

  • To: mathgroup at smc.vnet.net
  • Subject: [mg66472] Re: Limit Question
  • From: "Stratocaster" <stotz1 at verizon.net>
  • Date: Sun, 14 May 2006 02:58:31 -0400 (EDT)
  • References: <e43vun$90e$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

"Blimbaum, Jerry CIV NSWC PC" <jerry.blimbaum at navy.mil> wrote in message 
news:e43vun$90e$1 at smc.vnet.net...
>
> Why do these give no output?
>
> Simplify[Limit[Exp[-a t],t->Infinity],a>0]
>
> and  same for
>
> Simplify[Limit[Exp[a t],t->Infinity],a<0]
>
> thanks...
>
> Jerry Blimbaum

Well, that is a pretty good question, although I probably cannot give the 
"best" answer I'll put my two cents in for what it's worth.

The first thing that comes to mind is the expressions and the values for 
"a."  Take for example the first expression.  IF "Exp[-a*t]" AND "a>0" THEN 
"t" must be negative.  So I suggest :

Simplify[Limit[Exp[a*(-t)],t->Infinity],a>0];

In which case you don't really need the "Simplify" or  the condition for 
"a":

Limit[Exp[a*(-t)],t->Infinity];

I believe there is something similar going on in the second equation.  Make 
your limit expression correspond to your condition for "a" and you will not 
need to add anything extraneous to your "Limit" code.  I'm not sure if you 
just wanted to evaluate the limits or are asking specifics on why 
Mathematica isn't responding well to your input.  Hopefully this helps.






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