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Re: Trouble with Limit[I ... k]/k, k-> Infinity]
*To*: mathgroup at smc.vnet.net
*Subject*: [mg56167] Re: [mg56120] Trouble with Limit[I ... k]/k, k-> Infinity]
*From*: Daniel Lichtblau <danl at wolfram.com>
*Date*: Sun, 17 Apr 2005 03:07:21 -0400 (EDT)
*References*: <200504160751.DAA24601@smc.vnet.net>
*Sender*: owner-wri-mathgroup at wolfram.com
Christian Mikkelsen wrote:
> I am struggling to valuate an intermediate result in a long calculation
> and I get stuck with terms like this one:
>
> Limit[Exp[I k A]/k, k -> Infinity, Assumptions -> {A != 0, A \[Element]
> Reals}]
>
> In the actual expression, A are somewhat more complicated expressions but
> I am willing to tell Mathematica by hand that they are real and
> non-zero, however, it still doesn't work. I don't see that there is a
> problem in mathematical terms so how can I convince Mathematica to
> give me an answer?
>
> Actually, Mathematica 5.1 does not mind telling me the result of
>
> Limit[Exp[I k]/k, k -> Infinity]
>
> At the moment I am relying on a kludge relying on pattern-matching but I
> am not very good at it so there might be a point to help me on.
> Any input or help will be greatly appreciated.
>
>
> Thanks,
>
> Christian
It is slightly tricky for the Limit code to figure out that
there are two possibilities that behave in the same way. If you do
Limit[Exp[I*k*t]/k, k->Infinity, Assumptions->t>0]
or
Limit[Exp[I*k*t]/k, k->Infinity, Assumptions->t<0]
you get zero. I guess this means you will need to split into cases in
such situations.
Daniel Lichtblau
Wolfram Research
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