Re: What am I doing wrong?
- To: mathgroup at smc.vnet.net
- Subject: [mg91601] Re: What am I doing wrong?
- From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
- Date: Thu, 28 Aug 2008 07:40:21 -0400 (EDT)
- Organization: The Open University, Milton Keynes, UK
- References: <g95k5j$51m$1@smc.vnet.net>
Jack L Goldberg 1 wrote: > In(1) SeriesCoefficient[1/(1-x),{x,0,n}] > > Out(1) (-1)^n*Binomial[-1,n] > > Next, > > In(2) FunctionExpand[(-1)^n*Binomial[-1,n],Assumptions->Element[n,Integers]] > > OUt(2) ComplexInfinity > > In(3) Table[(-1)^n*Binomial[-1,n], {n,-2,2}] > > Out(3) {0,0,1,1,1} > > Incidentally, FullSimplify in place of FunctionExpand yields the same > result, ComplexInfinity. I wonder if this misleading answer is a > result of FunctionExpand and FullSymplify resorting to the Gamma > Function for the simplification? > > Is this a bug or a feature? > > Thanks, > > Jack You should tell Mathematica that n is a non-negative integer: In[1]:= Assuming[Element[n, Integers] && n >= 0, FunctionExpand[(-1)^n*Binomial[-1, n]]] Out[1]= (-1)^(2 n) In[2]:= Assuming[Element[n, Integers] && n < 0, FunctionExpand[(-1)^n*Binomial[-1, n]]] Out[2]= -1 In[3]:= Assuming[Element[n, Integers] && n >= -3, FunctionExpand[(-1)^n*Binomial[-1, n]]] Out[3]= ComplexInfinity Regards, -- Jean-Marc