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 > >