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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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