Re: Is this normal for Limit?

• To: mathgroup at smc.vnet.net
• Subject: [mg82287] Re: Is this normal for Limit?
• From: "Kevin J. McCann" <Kevin.McCann at umbc.edu>
• Date: Wed, 17 Oct 2007 03:54:30 -0400 (EDT)
• Organization: University System of Maryland
• References: <ff1par\$8nq\$1@smc.vnet.net>

```There are two problems:

1) I think the \$Pre definition below is applied to \$Assumptions so when
you look at the variable you get {t\[Element]Reals,True,True}.

2) The second problem appears to be a bug. If I reset \$Pre and leave the
\$Assumptions alone, I get

Limit[\[ExponentialE]^(-k t), t -> \[Infinity]]

just repeated, i.e. Mathematica doesn't evaluate; however, if I explicitly
include Assumptions in the call, I get the correct answer:

Limit[\[ExponentialE]^(-k t), t -> \[Infinity],
Assumptions :> {t \[Element] Reals, k \[Element] Reals, k > 0}]

0

Michael Mandelberg wrote:
> I have what I would think is the following simple limit to evaluate:
>
> \$Pre = Refine[#] &;
> \$Assumptions = {t \[Element] Reals, k \[Element] Reals,  k > 0};
>
> In[3]:= Limit[Exp[-k t], t -> Infinity]
>
> The results is:
>
> Out[3]= Limit[\[ExponentialE]^(-k t), t -> \[Infinity]]
>
> In other words Mathematica 6.0.0 punts on this.  Is there any sense in
> which this limit is not well-defined?
>
> Michael Mandelberg
>
>

```

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