Re: Trouble with Limit[I ... k]/k, k-> Infinity]

*To*: mathgroup at smc.vnet.net*Subject*: [mg56159] Re: Trouble with Limit[I ... k]/k, k-> Infinity]*From*: "David W. Cantrell" <DWCantrell at sigmaxi.org>*Date*: Sun, 17 Apr 2005 03:07:04 -0400 (EDT)*References*: <d3qgs6$oao$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Christian Mikkelsen <s010132 at student.dtu.dk> 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. My suggestion is to use ComplexExpand prior to asking for the limit. (I also dropped the condition that A be nonzero since it seemed irrelevant.) In[3]:= Assuming[Element[A, Reals], Limit[ComplexExpand[Exp[I*A*k]]/k, k -> Infinity]] Out[3]= 0 David