Re: Bug in Sum?

*To*: mathgroup at smc.vnet.net*Subject*: [mg120035] Re: Bug in Sum?*From*: Bob Hanlon <hanlonr at cox.net>*Date*: Wed, 6 Jul 2011 08:28:56 -0400 (EDT)*Reply-to*: hanlonr at cox.net

You can also try summing the parts Sum[#, {n, 1, M}] & /@ Apart[1/(n (1 + n)) 1/((1 - x)^4), n] // FullSimplify M/((1 + M) (-1 + x)^4) Bob Hanlon ---- Dario <dario.benedetti at aei.mpg.de> wrote: ============= Thanks Phil, I tried both with version 7 (Mac and Windows) and 8 (Mac) and it doesn't work. Bob, thanks for the suggestion, but the real problem is more complicated, I get some long and complicated output from some previous stuff, and as I couldn't sum it I discovered this bug. > Works in version 6.0 > > In[1]:= Sum[1/(n (1 + n)) 1/((1 - x)^4), {n, 1, M}] > $Version > > Out[1]= M/((1 + M) (1 - x)^4) > > Out[2]= "6.0 for Microsoft Windows (32-bit) (June 19, > 2007)" > > On Thu, Jun 30, 2011 at 6:29 AM, Bob Hanlon > <hanlonr at cox.net> wrote: > > > > > For a workaround, generalize the problem > > > > Sum[1/(n (1 + n)) 1/((1 - x)^r), {n, 1, M}] > > > > M/((1 - x)^r*(1 + M)) > > > > % /. r -> 4 > > > > M/((1 + M)*(1 - x)^4) > > > > > > Bob Hanlon > > > > ---- Dario <dario.benedetti at aei.mpg.de> wrote: > > > > ============= > > I am very puzzled by the fact that Mathematica does > not evaluate the > > following Sum (it keeps running endlessly): > > > > Sum[1/(n (1 + n)) 1/((1 - x)^4) , {n, 1, M}] > > > > where x and M are some undefined variables, > > > > but it does evaluate > > > > Sum[1/(n (1 + n)) 1/((1 - x)^2) , {n, 1, M}] > > > > where I have only changed the power of (1-x), which > should not matter as it > > must factor out! > > > > Any help on this please? > >